Evaluating natriuretic peptides in hyperthyroid cats

Menaut P, Connolly DJ, Volk A, et al. Circulating natriuretic peptide concentrations in hyperthyroid cats. J Small Anim Pract. 2012; 53: 673-8.

Natriuretic peptides (NPs) are neurohormones stored in heart muscle cells (atrial cardiomyocytes) and released in response to atrial stretch. They possess potent natriuretic and vasorelaxant properties. They have been shown to be chronically up-regulated in cats with underlying heart disease and have thus been used as a biomarker to detect occult heart disease and differentiate cardiac from non-cardiac dyspnea in emergency situations. In particular, the non-biologically active N-terminal fragment from atrial natriuretic peptide, (NT-proANP), and from brain natriuretic peptide, NT-proBNP, have commonly been studied due to their stability in plasma. 

Hyperthyroidism is the most common endocrine disease of cats. In humans with hyperthyroidism, a number of studies have shown NP concentrations to be elevated. Therefore, since NP measurement is increasingly being used to assess feline cardiac disease, determining the influence of elevated thyroid function on NP concentrations is essential.

In this study, 61 hyperthyroid cats were assessed before and after treatment for hyperthyroidism. Treatment included using methimazole or methimazole and subsequent surgical thyroidectomy. Cats with overt heart failure or systemic hypertension were excluded from the study due to previous reports showing these conditions to be associated with an increase in NT-proBNP. Assessment included full physical examination, systolic blood pressure (SBP), plasma biochemistries, total thyroid level (TT4), packed cell volume (PCV), and urinalysis, as well as measurement of NT-proBNP and NT-proANP concentrations. The length of time between pre- and post-treatment evaluation was 35 days and the length of time that the cats were on treatment before post-treatment sample was 28 days. Total T4, heart rate, SBP, and PCV all decreased and body weight and creatinine concentrations increased once euthyroidism was established. In addition, NT-proBNP significantly declined, but no change in NT-proANP concentrations was noted. In conclusion, hyperthyroidism has a modest but significant effect on elevating NT-proBNP with little effect on NT-proANP. Therefore, thyroid status should be taken into account when interpreting NT-proBNP results. [GO]

See also: Singletary GE, Rush JE, Fox PR, Stepien RL and Oyama MA. Effect of NT-pro-BNP assay on accuracy and confidence of general practitioners in diagnosing heart failure or respiratory disease in cats with respiratory signs. J Vet Intern Med. 2012; 26: 542-6.

Related blog articles:
Biochemical testing for feline heart disease (March 2009)
Cardiac biomarkers in feline heart disease (July 2011)

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Menaut P, Connolly DJ, Volk A, et al. Circulating natriuretic peptide concentrations in hyperthyroid cats. J Small Anim Pract. 2012; 53: 673-8.

Natriuretic peptides (NPs) are neurohormones stored in heart muscle cells (atrial cardiomyocytes) and released in response to atrial stretch. They possess potent natriuretic and vasorelaxant properties. They have been shown to be chronically up-regulated in cats with underlying heart disease and have thus been used as a biomarker to detect occult heart disease and differentiate cardiac from non-cardiac dyspnea in emergency situations. In particular, the non-biologically active N-terminal fragment from atrial natriuretic peptide, (NT-proANP), and from brain natriuretic peptide, NT-proBNP, have commonly been studied due to their stability in plasma. 

Hyperthyroidism is the most common endocrine disease of cats. In humans with hyperthyroidism, a number of studies have shown NP concentrations to be elevated. Therefore, since NP measurement is increasingly being used to assess feline cardiac disease, determining the influence of elevated thyroid function on NP concentrations is essential.

In this study, 61 hyperthyroid cats were assessed before and after treatment for hyperthyroidism. Treatment included using methimazole or methimazole and subsequent surgical thyroidectomy. Cats with overt heart failure or systemic hypertension were excluded from the study due to previous reports showing these conditions to be associated with an increase in NT-proBNP. Assessment included full physical examination, systolic blood pressure (SBP), plasma biochemistries, total thyroid level (TT4), packed cell volume (PCV), and urinalysis, as well as measurement of NT-proBNP and NT-proANP concentrations. The length of time between pre- and post-treatment evaluation was 35 days and the length of time that the cats were on treatment before post-treatment sample was 28 days. Total T4, heart rate, SBP, and PCV all decreased and body weight and creatinine concentrations increased once euthyroidism was established. In addition, NT-proBNP significantly declined, but no change in NT-proANP concentrations was noted. In conclusion, hyperthyroidism has a modest but significant effect on elevating NT-proBNP with little effect on NT-proANP. Therefore, thyroid status should be taken into account when interpreting NT-proBNP results. [GO]

See also: Singletary GE, Rush JE, Fox PR, Stepien RL and Oyama MA. Effect of NT-pro-BNP assay on accuracy and confidence of general practitioners in diagnosing heart failure or respiratory disease in cats with respiratory signs. J Vet Intern Med. 2012; 26: 542-6.

Related blog articles:
Biochemical testing for feline heart disease (March 2009)
Cardiac biomarkers in feline heart disease (July 2011)

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Hyperthyroidism and kidney disease in cats

Williams TL, Elliott J and Syme HM. Calcium and phosphate homeostasis in hyperthyroid cats – associations with development of azotaemia and survival time. J Small Anim Pract. 2012; 53: 561-71. 

Hyperthyroidism and chronic kidney disease (CKD) are common conditions of older cats that frequently occur concurrently. Hyperthyroid cats often have increased plasma phosphate concentrations and concomitantly increased plasma parathyroid hormone (PTH) concentrations. PTH is regarded as a uremic toxin and elevated levels have been postulated to contribute to renal damage or increased morbidity and mortality in feline hyperthyroidism. In addition, secondary renal hyperparathyroidism may also contribute to the progression of CKD in cats. Fibroblast growth factor-23 (FGF-23) is a phosphatonin secreted by osteoblasts in response to increased plasma phosphate and calcitriol concentrations. FGF-23 inhibits renal phosphate reabsorption, increasing phosphate urinary loss. In humans, serum FGF-23 concentrations predict the progression of CKD and both PTH and FGF-23 concentrations have been positively associated with all-cause mortality. It is unclear whether PTH and FGF-23 represent biomarkers of or mediate renal disease progression. Nevertheless, the association of PTH and FGF-23 with renal disease progression warrants evaluation of their concentration in hyperthyroid cats before and after treatment.

This study evaluated calcium and phosphate homeostasis in 207 hyperthyroid cats before and after treatment for hyperthyroidism by measuring plasma calcium, phosphate, PTH and FGF-23 concentrations. Patient selection was from records obtained from two London-based first-opinion practices between 1999 and 2009 and from newly diagnosed hyperthyroid cats. Twenty-eight healthy non-azotemic geriatric cats were also recruited in the study as controls. Hyperthyroid cats were treated with anti-thyroid medications (carbimazole or methimazole) alone or in combination with thyroidectomy. Hyperthyroid cats were divided into three groups: cats with pre-existing azotemia, cats that developed azotemia within 240 days after treatment and maintained euthyroidism, and cats which remained non-azotemic for at least 240 days after treatment and maintained euthyroidism. 

Results suggest that approximately 60% of hyperthyroid cats have elevated plasma PTH concentrations. Hyperthyroid cats without azotemia had hypocalcemia and hyperphosphatemia that would elevate PTH; however, the cause of decreased calcium and increased phosphate is unknown. There was no statistical difference in PTH levels for the three groups of hyperthyroid cats before treatment. PTH concentrations decreased following treatment in hyperthyroid cats that remained non-azotemic and remained elevated in cats that were or developed azotemia, suggesting secondary renal hyperparathyroidism in cats with azotemic CKD. 

FGF-23 concentrations were significantly higher in hyperthyroid cats with azotemia or that developed azotemia compared with cats that remained non-azotemic. Unexpectedly, plasma FGF-23 concentrations increased following treatment in cats with or without azotemic CKD independent of plasma phosphate concentrations, suggesting FGF-23 levels are suppressed in feline hyperthyroidism. The authors speculate that this increase in FGF-23 levels occurs secondary to the reduction in glomerular filtration rate after control of the hyperthyroid condition. FGF-23 was shown to be negatively associated with survival time when adjusted for age, creatinine, total calcium, phosphate, and PTH, but this association was lost when further adjustment factors were considered. Interestingly, omission of packed cell volume (PCV) as an explanatory variable resulted in FGF-23 again being associated with all-cause mortality, suggesting that FGF-23 influences survival time possibly by causing a reduction in PCV. [GO]

See also: Williams TL, Peak KJ, Brodbelt D, Elliott J and Syme HM. Survival and the development of azotemia after treatment of hyperthyroid cats. J Vet Intern Med. 2010; 24: 863-9.

For more information: other blog articles on hyperthyroidism

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Williams TL, Elliott J and Syme HM. Calcium and phosphate homeostasis in hyperthyroid cats – associations with development of azotaemia and survival time. J Small Anim Pract. 2012; 53: 561-71. 

Hyperthyroidism and chronic kidney disease (CKD) are common conditions of older cats that frequently occur concurrently. Hyperthyroid cats often have increased plasma phosphate concentrations and concomitantly increased plasma parathyroid hormone (PTH) concentrations. PTH is regarded as a uremic toxin and elevated levels have been postulated to contribute to renal damage or increased morbidity and mortality in feline hyperthyroidism. In addition, secondary renal hyperparathyroidism may also contribute to the progression of CKD in cats. Fibroblast growth factor-23 (FGF-23) is a phosphatonin secreted by osteoblasts in response to increased plasma phosphate and calcitriol concentrations. FGF-23 inhibits renal phosphate reabsorption, increasing phosphate urinary loss. In humans, serum FGF-23 concentrations predict the progression of CKD and both PTH and FGF-23 concentrations have been positively associated with all-cause mortality. It is unclear whether PTH and FGF-23 represent biomarkers of or mediate renal disease progression. Nevertheless, the association of PTH and FGF-23 with renal disease progression warrants evaluation of their concentration in hyperthyroid cats before and after treatment.

This study evaluated calcium and phosphate homeostasis in 207 hyperthyroid cats before and after treatment for hyperthyroidism by measuring plasma calcium, phosphate, PTH and FGF-23 concentrations. Patient selection was from records obtained from two London-based first-opinion practices between 1999 and 2009 and from newly diagnosed hyperthyroid cats. Twenty-eight healthy non-azotemic geriatric cats were also recruited in the study as controls. Hyperthyroid cats were treated with anti-thyroid medications (carbimazole or methimazole) alone or in combination with thyroidectomy. Hyperthyroid cats were divided into three groups: cats with pre-existing azotemia, cats that developed azotemia within 240 days after treatment and maintained euthyroidism, and cats which remained non-azotemic for at least 240 days after treatment and maintained euthyroidism. 

Results suggest that approximately 60% of hyperthyroid cats have elevated plasma PTH concentrations. Hyperthyroid cats without azotemia had hypocalcemia and hyperphosphatemia that would elevate PTH; however, the cause of decreased calcium and increased phosphate is unknown. There was no statistical difference in PTH levels for the three groups of hyperthyroid cats before treatment. PTH concentrations decreased following treatment in hyperthyroid cats that remained non-azotemic and remained elevated in cats that were or developed azotemia, suggesting secondary renal hyperparathyroidism in cats with azotemic CKD. 

FGF-23 concentrations were significantly higher in hyperthyroid cats with azotemia or that developed azotemia compared with cats that remained non-azotemic. Unexpectedly, plasma FGF-23 concentrations increased following treatment in cats with or without azotemic CKD independent of plasma phosphate concentrations, suggesting FGF-23 levels are suppressed in feline hyperthyroidism. The authors speculate that this increase in FGF-23 levels occurs secondary to the reduction in glomerular filtration rate after control of the hyperthyroid condition. FGF-23 was shown to be negatively associated with survival time when adjusted for age, creatinine, total calcium, phosphate, and PTH, but this association was lost when further adjustment factors were considered. Interestingly, omission of packed cell volume (PCV) as an explanatory variable resulted in FGF-23 again being associated with all-cause mortality, suggesting that FGF-23 influences survival time possibly by causing a reduction in PCV. [GO]

See also: Williams TL, Peak KJ, Brodbelt D, Elliott J and Syme HM. Survival and the development of azotemia after treatment of hyperthyroid cats. J Vet Intern Med. 2010; 24: 863-9.

For more information: other blog articles on hyperthyroidism

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Hyperthyroidism and kidney disease in cats

Progress report, Winn grant 09-013
Identification of a biomarker for masked renal failure in hyperthyroid cats
Investigator: Thomas Schermerhorn, Kansas State University and collaborators
 
These researchers are trying to improve diagnosis and prognosis of cats with both hyperthyroidism and kidney disease, two common ailments of aging cats. Often, hyperthyroidism masks underlying kidney disease until it is revealed during treatment. The investigators are attempting to define a method for identifying the kidney disease before treatment of hyperthyroidism. This would improve the well-being of the cat as well as its life expectancy. To do this, they are analyzing the urine of hyperthyroid cats using a cutting-edge technique to identify literally thousands of urine components to see if any correlate with post-treatment appearance of kidney disease.

It has been a challenge acquiring sufficient numbers of cases of cats with hyperthyroidism able to participate in the study. Despite this, analysis is ongoing. To date, no identifiable correlate with renal disease has been found. However, the urine composition of hyperthyroid cats has been determined at a much more detailed level, which may allow future diagnosis of this condition via a simple urine test. [MK]

See also: Riensche MR, Graves TK, Schaeffer DJ. An investigation of predictors of renal insufficiency following treatment of hyperthyroidism in cats. J Feline Med Surg 2008;10:160-166.

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Progress report, Winn grant 09-013
Identification of a biomarker for masked renal failure in hyperthyroid cats
Investigator: Thomas Schermerhorn, Kansas State University and collaborators
 
These researchers are trying to improve diagnosis and prognosis of cats with both hyperthyroidism and kidney disease, two common ailments of aging cats. Often, hyperthyroidism masks underlying kidney disease until it is revealed during treatment. The investigators are attempting to define a method for identifying the kidney disease before treatment of hyperthyroidism. This would improve the well-being of the cat as well as its life expectancy. To do this, they are analyzing the urine of hyperthyroid cats using a cutting-edge technique to identify literally thousands of urine components to see if any correlate with post-treatment appearance of kidney disease.

It has been a challenge acquiring sufficient numbers of cases of cats with hyperthyroidism able to participate in the study. Despite this, analysis is ongoing. To date, no identifiable correlate with renal disease has been found. However, the urine composition of hyperthyroid cats has been determined at a much more detailed level, which may allow future diagnosis of this condition via a simple urine test. [MK]

See also: Riensche MR, Graves TK, Schaeffer DJ. An investigation of predictors of renal insufficiency following treatment of hyperthyroidism in cats. J Feline Med Surg 2008;10:160-166.

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Medical Treatment for Feline Hyperthyroidism

Longhofer S, Martin-Jimenez T, Soni-Gupta J: Serum concentrations of methimazole in cats after a single oral dose of controlled-release carbimazole or sugar-coated methimazole (thiamazole), Vet Ther 11:E1, 2010. 

Hyperthyroidism is the most common endocrine disorder in middle-aged and older cats. Medical management with the antithyroid drug methimazole has become a popular option, either before surgery (thyroidectomy) or radioiodine treatment, or for long-term medical management. Carbimazole is rapidly metabolized to methimazole in vivo. This cross-over study of 6 normal cats compared a single oral dose of either a controlled-release carbimazole tablet or a sugar-coated methimazole tablet. Both formulations are approved for use in cats and were found to be well tolerated by the cats in the course of the study. In general, the pharmacokinetic values for the two treatments were similar when differences in effective methimazole dose were taken into consideration. Both drugs were reported to have relatively short plasma half-lives in the current study that would seem to support either once or twice daily dosing for either. Methimazole accumulates in the thyroid gland so that antithyroid effects extend beyond (possibly up to 24 hours) the duration of elevated plasma levels.  Therefore, the short half-life of 3 hours for both controlled-release carbimazole and sugar-coated methimazole tablets is consistent with current practice recommendations for divided daily dosing, although once-daily dosing may be appropriate for maintenance therapy in some cats. [VT]

Related articles:

Frenais R, Rosenberg D, Burgaud S et al: Clinical efficacy and safety of a once-daily formulation of carbimazole in cats with hyperthyroidism, J Small Anim Pract 50:510, 2009.

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Longhofer S, Martin-Jimenez T, Soni-Gupta J: Serum concentrations of methimazole in cats after a single oral dose of controlled-release carbimazole or sugar-coated methimazole (thiamazole), Vet Ther 11:E1, 2010. 

Hyperthyroidism is the most common endocrine disorder in middle-aged and older cats. Medical management with the antithyroid drug methimazole has become a popular option, either before surgery (thyroidectomy) or radioiodine treatment, or for long-term medical management. Carbimazole is rapidly metabolized to methimazole in vivo. This cross-over study of 6 normal cats compared a single oral dose of either a controlled-release carbimazole tablet or a sugar-coated methimazole tablet. Both formulations are approved for use in cats and were found to be well tolerated by the cats in the course of the study. In general, the pharmacokinetic values for the two treatments were similar when differences in effective methimazole dose were taken into consideration. Both drugs were reported to have relatively short plasma half-lives in the current study that would seem to support either once or twice daily dosing for either. Methimazole accumulates in the thyroid gland so that antithyroid effects extend beyond (possibly up to 24 hours) the duration of elevated plasma levels.  Therefore, the short half-life of 3 hours for both controlled-release carbimazole and sugar-coated methimazole tablets is consistent with current practice recommendations for divided daily dosing, although once-daily dosing may be appropriate for maintenance therapy in some cats. [VT]

Related articles:

Frenais R, Rosenberg D, Burgaud S et al: Clinical efficacy and safety of a once-daily formulation of carbimazole in cats with hyperthyroidism, J Small Anim Pract 50:510, 2009.

More on cat health: Winn Feline Foundation Library

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Multiple Endocrine Diseases in Cats

Blois SL, Dickie EL, Kruth SA et al: Multiple endocrine diseases in cats: 15 cases (1997–2008), J Feline Med Surg 12: 637, 2010. 

Multiple endocrine glandular failure is a recognized syndrome in humans, yet it is an uncommonly recognized phenomenon in veterinary medicine. This is a retrospective study characterizing a population of cats from a university veterinary teaching hospital diagnosed with multiple endocrine disorders. The medical records of 15 cats diagnosed with more than one endocrine disease were reviewed. The most common combination of endocrine disorders noted was hyperthyroidism and diabetes mellitus, making up 11 of 15 cases. Two of 15 cases had concurrent diabetes mellitus and hyperadrenocorticism. One other cat had concurrent diabetes mellitus and central diabetes insipidus, while another was diagnosed with hyperthyroidism and hyperparathyroidism.  A majority of the cases were domestic shorthair cats with the mean age of 10.3 years and a mean of 25.7 months elapsing between the diagnosis of the first and second endocrine disorder. The authors’ results suggest the occurrence of multiple endocrine disorders in cats is uncommon. [VT]

Related articles:

Gunn-Moore D: Feline endocrinopathies, Vet Clin North Am Small Anim Pract 35: 171, 2005.

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Blois SL, Dickie EL, Kruth SA et al: Multiple endocrine diseases in cats: 15 cases (1997–2008), J Feline Med Surg 12: 637, 2010. 

Multiple endocrine glandular failure is a recognized syndrome in humans, yet it is an uncommonly recognized phenomenon in veterinary medicine. This is a retrospective study characterizing a population of cats from a university veterinary teaching hospital diagnosed with multiple endocrine disorders. The medical records of 15 cats diagnosed with more than one endocrine disease were reviewed. The most common combination of endocrine disorders noted was hyperthyroidism and diabetes mellitus, making up 11 of 15 cases. Two of 15 cases had concurrent diabetes mellitus and hyperadrenocorticism. One other cat had concurrent diabetes mellitus and central diabetes insipidus, while another was diagnosed with hyperthyroidism and hyperparathyroidism.  A majority of the cases were domestic shorthair cats with the mean age of 10.3 years and a mean of 25.7 months elapsing between the diagnosis of the first and second endocrine disorder. The authors’ results suggest the occurrence of multiple endocrine disorders in cats is uncommon. [VT]

Related articles:

Gunn-Moore D: Feline endocrinopathies, Vet Clin North Am Small Anim Pract 35: 171, 2005.

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Feline Hyperthyroidism and Kidney Disease

Williams T, Elliott J, Syme H: Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism, J Vet Intern Med 24:1086, 2010.

Within 6 months of treatment of hyperthyroidism, 17-49% of cats develop azotemia. Treatment to restore euthyroidism in cats results in a decrease in renal glomerular filtration rate (GFR) which can lead to the development of azotemia if underlying chronic renal disease (CRD) is present. Antithyroid treatment could lead to iatrogenic hypothyroidism and hypothyroidism has been correlated with reduced GFR. The authors performed two retrospective studies. The first study was of 12 hyperthyroid cats treated with radioiodine and documented as euthyroid after treatment where changes were assessed in plasma thyroid stimulating hormone (TSH) concentration over a 6-month follow-up period. The second study was of 75 hyperthyroid cats, documented as euthyroid, that were monitored 6 months after starting treatment to identify the relationship between thyroid status and the development of azotemia. Plasma TSH concentrations were not suppressed in 7 of 8 cats with hypothyroidism 3 months after radioiodine treatment. The study concluded that cats with iatrogenic hypothyroidism were more likely to develop azotemia within 6 months after treatment for hyperthyroidism than cats defined as euthyroid. Hypothyroid cats with azotemia had shorter survival times than non-azotemic cats.  There was no difference in survival times of euthyroid cats with or without azotemia.  [VT]

Related articles:
Williams TL, Peak KJ, Brodbelt D et al: Survival and the development of azotemia after treatment of hyperthyroid cats, J Vet Intern Med 24:863, 2010.

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Williams T, Elliott J, Syme H: Association of iatrogenic hypothyroidism with azotemia and reduced survival time in cats treated for hyperthyroidism, J Vet Intern Med 24:1086, 2010.

Within 6 months of treatment of hyperthyroidism, 17-49% of cats develop azotemia. Treatment to restore euthyroidism in cats results in a decrease in renal glomerular filtration rate (GFR) which can lead to the development of azotemia if underlying chronic renal disease (CRD) is present. Antithyroid treatment could lead to iatrogenic hypothyroidism and hypothyroidism has been correlated with reduced GFR. The authors performed two retrospective studies. The first study was of 12 hyperthyroid cats treated with radioiodine and documented as euthyroid after treatment where changes were assessed in plasma thyroid stimulating hormone (TSH) concentration over a 6-month follow-up period. The second study was of 75 hyperthyroid cats, documented as euthyroid, that were monitored 6 months after starting treatment to identify the relationship between thyroid status and the development of azotemia. Plasma TSH concentrations were not suppressed in 7 of 8 cats with hypothyroidism 3 months after radioiodine treatment. The study concluded that cats with iatrogenic hypothyroidism were more likely to develop azotemia within 6 months after treatment for hyperthyroidism than cats defined as euthyroid. Hypothyroid cats with azotemia had shorter survival times than non-azotemic cats.  There was no difference in survival times of euthyroid cats with or without azotemia.  [VT]

Related articles:
Williams TL, Peak KJ, Brodbelt D et al: Survival and the development of azotemia after treatment of hyperthyroid cats, J Vet Intern Med 24:863, 2010.

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Thyroid Testing in Cats

van Hoek IM, Vandermeulen E, Peremans K et al: Thyroid stimulation with recombinant human thyrotropin in healthy cats, cats with non-thyroidal illness and in cats with low serum thyroxin and azotaemia after treatment of hyperthyroidism, J Feline Med Surg 12:117, 2010.

Investigators studied the recombinant human thyrotropin (rhTSH) stimulation test in healthy cats (Group 1), cats with non-thyroidal illness (Group 2) and cats with low serum total T4 (TT4) and azotemia after I-131 treatment (Group 3). Radioiodine (131)is the treatment of choice for hyperthyroidism, yet iatrogenic hypothyroidism can occur in 6-30% of cases post-treatment. Complicating this, up to 39% of treated cats have chronic kidney disease (CKD). When a low circulating serum TT4 concentration is found in cats treated with I-131, non-thyroidal illness (NTI) has to be considered, especially CKD, before a diagnosis of iatrogenic hypothyroidism can be confirmed. With the consideration that hypothyroidism can decrease renal function, a diagnosis of hypothyroidism or NTI is necessary. Serum TT4 increased significantly in groups 1 and 2, but not in group 3 after rhTSH administration. Post-rhTSH serum TT4 concentrations differed significantly between groups 1 and 3 and groups 2 and 3, but not between groups 1 and 2. Based on the marginal increase in serum TT4 concentration, compared to the healthy cats and cats with NTI, the conclusion was that all four cats from Group 3 had iatrogenic hypothyroidism. The study results suggest a TT4 measurement before and after rhTSH is a clinically useful test and can reliably evaluate thyroid function and differentiate euthyroidism from iatrogenic hypothyroidism in cats. [VT]

Related articles:
van Hoek IM, Peremans K, Vandermeulen E et al: Effect of recombinant human thyroid stimulating hormone on serum thyroxin and thyroid scintigraphy in euthyroid cats, Journal of Feline Medicine & Surgery 11:309, 2009.

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van Hoek IM, Vandermeulen E, Peremans K et al: Thyroid stimulation with recombinant human thyrotropin in healthy cats, cats with non-thyroidal illness and in cats with low serum thyroxin and azotaemia after treatment of hyperthyroidism, J Feline Med Surg 12:117, 2010.

Investigators studied the recombinant human thyrotropin (rhTSH) stimulation test in healthy cats (Group 1), cats with non-thyroidal illness (Group 2) and cats with low serum total T4 (TT4) and azotemia after I-131 treatment (Group 3). Radioiodine (131)is the treatment of choice for hyperthyroidism, yet iatrogenic hypothyroidism can occur in 6-30% of cases post-treatment. Complicating this, up to 39% of treated cats have chronic kidney disease (CKD). When a low circulating serum TT4 concentration is found in cats treated with I-131, non-thyroidal illness (NTI) has to be considered, especially CKD, before a diagnosis of iatrogenic hypothyroidism can be confirmed. With the consideration that hypothyroidism can decrease renal function, a diagnosis of hypothyroidism or NTI is necessary. Serum TT4 increased significantly in groups 1 and 2, but not in group 3 after rhTSH administration. Post-rhTSH serum TT4 concentrations differed significantly between groups 1 and 3 and groups 2 and 3, but not between groups 1 and 2. Based on the marginal increase in serum TT4 concentration, compared to the healthy cats and cats with NTI, the conclusion was that all four cats from Group 3 had iatrogenic hypothyroidism. The study results suggest a TT4 measurement before and after rhTSH is a clinically useful test and can reliably evaluate thyroid function and differentiate euthyroidism from iatrogenic hypothyroidism in cats. [VT]

Related articles:
van Hoek IM, Peremans K, Vandermeulen E et al: Effect of recombinant human thyroid stimulating hormone on serum thyroxin and thyroid scintigraphy in euthyroid cats, Journal of Feline Medicine & Surgery 11:309, 2009.

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Thyroid Hormone Testing

Rutland BE, Nachreiner RF, Kruger JM. Optimal testing for thyroid hormone concentration after treatment with methimazole in healthy and hyperthyroid cats. J Vet Intern Med 2009;23:1025-1030.

Hyperthyroidism is one of the most common endocrinopathies of cats and its prevalence is increasing in recent years. Methimazole is commonly used to treat hyperthyroidism and its action is to suppress thyroid hormone synthesis. The optimal time for blood sampling to monitor therapeutic efficacy, and the amount of variation in thyroid hormone concentrations 24 hours post administration of methimazole have not been determined. In this study, healthy cats were given steadily increasing doses of oral methimazole until a steady state of thyroid suppression was achieved. It was found that there is a significant and sustained suppression of total thyroxine (TT4), total tri-iodothyronine (TT3), free T3, and free T4 concentrations for 24 hours after a once daily methimazole administration in healthy cats. The time to thyroid gland suppression in healthy cats was 2-5 weeks. In addition, a retrospective study of 889 thyroid profiles from methimazole-treated hyperthyroid cats was reviewed. The review noted that in hyperthyroid cats, there was no significant relationship between thyroid hormone concentrations and time post-pill or dosing interval. The conclusion was timing of blood sampling after oral methimazole administration does not appear to be a significant factor when assessing response to treatment. [VT]
>> PubMed Abstract

Related articles:
Trepanier L, Hoffman S, Kroll M, et al. Efficacy and safety of once versus twice daily administration of methimazole in cats with hyperthyroidism. J Am Vet Med Assoc 2003;222:954-958.
>> PubMed Abstract

Trepanier LA. Pharmacologic management of feline hyperthyroidism. Vet Clin North Am Small Anim Pract 2007;37:775-788, vii.
>> PubMed Abstract

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Rutland BE, Nachreiner RF, Kruger JM. Optimal testing for thyroid hormone concentration after treatment with methimazole in healthy and hyperthyroid cats. J Vet Intern Med 2009;23:1025-1030.

Hyperthyroidism is one of the most common endocrinopathies of cats and its prevalence is increasing in recent years. Methimazole is commonly used to treat hyperthyroidism and its action is to suppress thyroid hormone synthesis. The optimal time for blood sampling to monitor therapeutic efficacy, and the amount of variation in thyroid hormone concentrations 24 hours post administration of methimazole have not been determined. In this study, healthy cats were given steadily increasing doses of oral methimazole until a steady state of thyroid suppression was achieved. It was found that there is a significant and sustained suppression of total thyroxine (TT4), total tri-iodothyronine (TT3), free T3, and free T4 concentrations for 24 hours after a once daily methimazole administration in healthy cats. The time to thyroid gland suppression in healthy cats was 2-5 weeks. In addition, a retrospective study of 889 thyroid profiles from methimazole-treated hyperthyroid cats was reviewed. The review noted that in hyperthyroid cats, there was no significant relationship between thyroid hormone concentrations and time post-pill or dosing interval. The conclusion was timing of blood sampling after oral methimazole administration does not appear to be a significant factor when assessing response to treatment. [VT]
>> PubMed Abstract

Related articles:
Trepanier L, Hoffman S, Kroll M, et al. Efficacy and safety of once versus twice daily administration of methimazole in cats with hyperthyroidism. J Am Vet Med Assoc 2003;222:954-958.
>> PubMed Abstract

Trepanier LA. Pharmacologic management of feline hyperthyroidism. Vet Clin North Am Small Anim Pract 2007;37:775-788, vii.
>> PubMed Abstract

More on cat health: Winn Feline Foundation Library
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Treatment of Feline Hyperthyroidism with Carbimazole

Frenais, R., et al., Clinical efficacy and safety of a once-daily formulation of carbimazole in cats with hyperthyroidism. J Small Anim Pract, 2009. 50(10): p. 510-5.

Traditionally, medical treatment of feline hyperthyroidism has involved daily use of the azole drugs, methimazole or its pro-drug, carbimazole. Many cats require twice daily treatment with these drugs. A novel controlled-release formulation of carbimazole (Vidalta) has been developed by Intervet. These researchers evaluated the efficacy and safety of this new carbimazole formulation via a multi-center study of 44 client-owned cats with hyperthyroidism. Treatment was started at 15 mg/cat once daily, and dose was adjusted as required. Cats were followed for 53 weeks. The median dose over the study period was 10-15 mg/cat once daily. Clinical signs improved in almost all cats within 3 weeks after treatment was started. An increase in blood urea nitrogen (BUN) was noted in 25% of the cats, eosinophilia was noted in 20%, and lymphopenia in 16%. The researchers conclude that once daily administration of controlled-release carbimazole is effective with acceptable tolerance during short and long term treatment of feline hyperthyroidism. [SL]
>> PubMed Abstract

Related articles:
Frenais, R., S. Burgaud, and L.J.I. Horspool, Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats. Journal of Veterinary Pharmacology and Therapeutics, 2008. 31(3): p. 213-219.
>> PubMed Abstract

Trepanier, L.A., Medical management of hyperthyroidism. Clin Tech Small Anim Pract, 2006. 21(1): p. 22-8.
>> PubMed Abstract

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Frenais, R., et al., Clinical efficacy and safety of a once-daily formulation of carbimazole in cats with hyperthyroidism. J Small Anim Pract, 2009. 50(10): p. 510-5.

Traditionally, medical treatment of feline hyperthyroidism has involved daily use of the azole drugs, methimazole or its pro-drug, carbimazole. Many cats require twice daily treatment with these drugs. A novel controlled-release formulation of carbimazole (Vidalta) has been developed by Intervet. These researchers evaluated the efficacy and safety of this new carbimazole formulation via a multi-center study of 44 client-owned cats with hyperthyroidism. Treatment was started at 15 mg/cat once daily, and dose was adjusted as required. Cats were followed for 53 weeks. The median dose over the study period was 10-15 mg/cat once daily. Clinical signs improved in almost all cats within 3 weeks after treatment was started. An increase in blood urea nitrogen (BUN) was noted in 25% of the cats, eosinophilia was noted in 20%, and lymphopenia in 16%. The researchers conclude that once daily administration of controlled-release carbimazole is effective with acceptable tolerance during short and long term treatment of feline hyperthyroidism. [SL]
>> PubMed Abstract

Related articles:
Frenais, R., S. Burgaud, and L.J.I. Horspool, Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats. Journal of Veterinary Pharmacology and Therapeutics, 2008. 31(3): p. 213-219.
>> PubMed Abstract

Trepanier, L.A., Medical management of hyperthyroidism. Clin Tech Small Anim Pract, 2006. 21(1): p. 22-8.
>> PubMed Abstract

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Risk Factors for Feline Hyperthyroidism

Wakeling J, Everard A, Brodbelt D, Elliott J, Syme H. Risk factors for feline hyperthyroidism in the UK. J Small Anim Pract 2009; 50: 406-14.

Hyperthyroidism is an important disease of cats, and while risk factors for cats in the USA and New Zealand have been studied, no equivalent study has been done for cats in the UK. These researchers investigated UK risk factors using a case-controlled questionnaire-based protocol. The study included 109 hyperthyroid cats, and 196 normal cats over eight years old as controls. They found that older cats were more likely to be affected with hyperthyroidism, while purebred animals were less likely to suffer hyperthyroidism. There was no difference in risk for males versus female in this study. In the univariate analysis, hyperthyroid cats were more likely to have used a litter box, to be fed wet cat food, to have been fed wet food from a can (as opposed to being fed wet food only from pouches), to be fed all categories of table food including high-fat dairy products, and were more likely to have been exposed to smokers in their environment and to household flea treatments. These findings were similar to those of previous studies. Exposure to food packaged in cans was identified as the major risk factor for the development of hyperthyroidism. [MK]
>> PubMed Abstract

Related articles:
Olczak J, Jones BR, Pfeiffer DU, Squires RA, Morris RS, Markwell PJ. Multivariate analysis of risk factors for feline hyperthyroidism in New Zealand. N Z Vet J 2005; 53: 53-8.
>> PubMed Abstract

Edinboro C, Scott-Moncrieff J, Janovitz E, al e. Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats. J Amer Vet Med Assoc 2004; 224: 879-886.
>> PubMed Abstract

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Wakeling J, Everard A, Brodbelt D, Elliott J, Syme H. Risk factors for feline hyperthyroidism in the UK. J Small Anim Pract 2009; 50: 406-14.

Hyperthyroidism is an important disease of cats, and while risk factors for cats in the USA and New Zealand have been studied, no equivalent study has been done for cats in the UK. These researchers investigated UK risk factors using a case-controlled questionnaire-based protocol. The study included 109 hyperthyroid cats, and 196 normal cats over eight years old as controls. They found that older cats were more likely to be affected with hyperthyroidism, while purebred animals were less likely to suffer hyperthyroidism. There was no difference in risk for males versus female in this study. In the univariate analysis, hyperthyroid cats were more likely to have used a litter box, to be fed wet cat food, to have been fed wet food from a can (as opposed to being fed wet food only from pouches), to be fed all categories of table food including high-fat dairy products, and were more likely to have been exposed to smokers in their environment and to household flea treatments. These findings were similar to those of previous studies. Exposure to food packaged in cans was identified as the major risk factor for the development of hyperthyroidism. [MK]
>> PubMed Abstract

Related articles:
Olczak J, Jones BR, Pfeiffer DU, Squires RA, Morris RS, Markwell PJ. Multivariate analysis of risk factors for feline hyperthyroidism in New Zealand. N Z Vet J 2005; 53: 53-8.
>> PubMed Abstract

Edinboro C, Scott-Moncrieff J, Janovitz E, al e. Epidemiologic study of relationships between consumption of commercial canned food and risk of hyperthyroidism in cats. J Amer Vet Med Assoc 2004; 224: 879-886.
>> PubMed Abstract

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Scintigraphy for Feline Hyperthyroidism

Harvey, A. M., A. Hibbert, et al. (2009). "Scintigraphic findings in 120 hyperthyroid cats." Journal of Feline Medicine & Surgery 11(2): 96-106.

The purpose of this study performed at the University of Bristol, United Kingdom, was to characterize the scintigraphic findings in a group of cats with hyperthyroidism to determine the location of the abnormal thyroid tissue. Thyroid scintigraphy relies on the selective uptake of a radionuclide by thyroid tissue. Hyperthyroidism is diagnosed by the increased level of uptake by the thyroid gland compared with salivary gland tissue. Thyroid scintigraphy also demonstrates the location of the abnormal thyroid tissue, which is useful when planning treatment options. The database of the Feline Centre at the University of Bristol was searched for cases of feline hyperthyroidism with good quality scintigraphic images between 1994 and 2007. Images from 120 cats were evaluated. Almost 1 in 5 hyperthyroid cats was found to have multiple areas of abnormal thyroid tissue and/or intrathoracic thyroid tissue where surgical thyroidectomy would not be curative. Another finding was that scintigraphy could not reliably differentiate between thyroid carcinoma and adenoma. The authors conclude that the possible presence of ectopic thyroid tissue should be discussed with all owners of hyperthyroid cats prior to performing surgical thyroidectomy. [SL]
>> PubMed Abstract

Related articles:
Henrikson, T. D., L. J. Armbrust, et al. (2005). "Thyroid to salivary ratios determined by technetium-99m pertechnetate imaging in thirty-two euthyroid cats." Vet Radiol Ultrasound 46(6): 521-3.
>> PubMed Abstract

Naan, E. C., J. Kirpensteijn, et al. (2006). "Results of thyroidectomy in 101 cats with hyperthyroidism." Vet Surg 35(3): 287-93.
>> PubMed Abstract

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Harvey, A. M., A. Hibbert, et al. (2009). "Scintigraphic findings in 120 hyperthyroid cats." Journal of Feline Medicine & Surgery 11(2): 96-106.

The purpose of this study performed at the University of Bristol, United Kingdom, was to characterize the scintigraphic findings in a group of cats with hyperthyroidism to determine the location of the abnormal thyroid tissue. Thyroid scintigraphy relies on the selective uptake of a radionuclide by thyroid tissue. Hyperthyroidism is diagnosed by the increased level of uptake by the thyroid gland compared with salivary gland tissue. Thyroid scintigraphy also demonstrates the location of the abnormal thyroid tissue, which is useful when planning treatment options. The database of the Feline Centre at the University of Bristol was searched for cases of feline hyperthyroidism with good quality scintigraphic images between 1994 and 2007. Images from 120 cats were evaluated. Almost 1 in 5 hyperthyroid cats was found to have multiple areas of abnormal thyroid tissue and/or intrathoracic thyroid tissue where surgical thyroidectomy would not be curative. Another finding was that scintigraphy could not reliably differentiate between thyroid carcinoma and adenoma. The authors conclude that the possible presence of ectopic thyroid tissue should be discussed with all owners of hyperthyroid cats prior to performing surgical thyroidectomy. [SL]
>> PubMed Abstract

Related articles:
Henrikson, T. D., L. J. Armbrust, et al. (2005). "Thyroid to salivary ratios determined by technetium-99m pertechnetate imaging in thirty-two euthyroid cats." Vet Radiol Ultrasound 46(6): 521-3.
>> PubMed Abstract

Naan, E. C., J. Kirpensteijn, et al. (2006). "Results of thyroidectomy in 101 cats with hyperthyroidism." Vet Surg 35(3): 287-93.
>> PubMed Abstract

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Atenolol for Hyperthyroid Cats

Henik, R. A., R. L. Stepien, et al. (2008). "Efficacy of atenolol as a single antihypertensive agent in hyperthyroid cats." Journal of Feline Medicine & Surgery 10(6): 577-582.

Hypertension is a common complication of hyperthyroidism and chronic renal disease in cats. Various drugs may be used to treat feline hypertension, but the drug of choice appears to be amlodipine due to its efficacy and low incidence of adverse effects. However, in cats with hypertension caused by hyperthyroidism, beta-blocking drugs such as atenolol have been suggested to slow the heart rate and block effects of thyroid hormone on the cardiovascular system. While atenolol has been shown to be ineffective in treating hypertension associated with chronic renal disease, it has not been previously investigated for treatment of cats with hyperthyroidism. In this retrospective study, 20 hyperthyroid cats with systolic blood pressure over 160 mmHg were treated with atenolol (1-2 mg/kg, PO, BID). All cats were treated for a minimum of 5 days before reassessment and treatment with radioactive iodine. While both heart rate and systolic blood pressure decreased in the cats, successful clinical control of blood pressure was not achieved in 70% of the cases. The investigators concluded that while atenolol successfully controls heart rate in hyperthyroid cats, the addition of another drug is needed to treat hypertension.
>> PubMed Abstract

Related articles:
Trepanier LA. Pharmacologic management of feline hyperthyroidism. Vet Clin North Am Small Anim Pract. 2007 Jul;37(4):775-88
>> PubMed Abstract

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Henik, R. A., R. L. Stepien, et al. (2008). "Efficacy of atenolol as a single antihypertensive agent in hyperthyroid cats." Journal of Feline Medicine & Surgery 10(6): 577-582.

Hypertension is a common complication of hyperthyroidism and chronic renal disease in cats. Various drugs may be used to treat feline hypertension, but the drug of choice appears to be amlodipine due to its efficacy and low incidence of adverse effects. However, in cats with hypertension caused by hyperthyroidism, beta-blocking drugs such as atenolol have been suggested to slow the heart rate and block effects of thyroid hormone on the cardiovascular system. While atenolol has been shown to be ineffective in treating hypertension associated with chronic renal disease, it has not been previously investigated for treatment of cats with hyperthyroidism. In this retrospective study, 20 hyperthyroid cats with systolic blood pressure over 160 mmHg were treated with atenolol (1-2 mg/kg, PO, BID). All cats were treated for a minimum of 5 days before reassessment and treatment with radioactive iodine. While both heart rate and systolic blood pressure decreased in the cats, successful clinical control of blood pressure was not achieved in 70% of the cases. The investigators concluded that while atenolol successfully controls heart rate in hyperthyroid cats, the addition of another drug is needed to treat hypertension.
>> PubMed Abstract

Related articles:
Trepanier LA. Pharmacologic management of feline hyperthyroidism. Vet Clin North Am Small Anim Pract. 2007 Jul;37(4):775-88
>> PubMed Abstract

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Feline Thyroid Palpation Techniques

Paepe, D., P. Smets, et al. (2008). "Within- and between-examiner agreement for two thyroid palpation techniques in healthy and hyperthyroid cats." Journal of Feline Medicine & Surgery 10(6): 558-565.

The most common endocrine disorder of senior cats is hyperthyroidism. Early diagnosis and treatment can prevent serious complications. One of the most important diagnostic tools is palpation of the thyroid gland for enlargement, a standard part of the physical examination, especially for senior cats. There are two thyroid palpation techniques for cats described in the literature. The classic technique has the cat in a sitting position with the neck extended. Another technique has the cat standing with the head elevated and turned to one side. The diagnostic value of these techniques has not been compared. In this prospective study, 9 client-owned hyperthyroid cats and 10 healthy control cats were examined twice by 3 blind-folded clinicians using each palpation technique. A score from 1 to 6 was assigned to thyroid gland size each time. After clipping the hair of the ventral neck region, a final palpation session was performed, followed by ultrasonography of the gland. The classic palpation technique led to smaller within- and between-examiner differences. Clipping the hair coat did not make a significant difference. While both thyroid palpation techniques had good within- and between-examiner results, the investigators concluded that the classic palpation technique is preferred.
>> PubMed Abstract

Related Articles:
Norsworthy, G., V. Adams, et al. (2002). "Relationship between semi-quantitative thyroid gland palpation and total thyroxine concentration in cats with an without hyperadrenocorticism." J Fel Med Surg 4(3): 139.
>> PubMed Abstract

Norsworthy, G., V. Adams, et al. (2002). "Palpable thyroid and parathyroid nodules in asymptomatic cats." J Fel Med Surg 4(3): 145.
>> PubMed Abstract

More on cat health: Winn Feline Foundation Library

Paepe, D., P. Smets, et al. (2008). "Within- and between-examiner agreement for two thyroid palpation techniques in healthy and hyperthyroid cats." Journal of Feline Medicine & Surgery 10(6): 558-565.

The most common endocrine disorder of senior cats is hyperthyroidism. Early diagnosis and treatment can prevent serious complications. One of the most important diagnostic tools is palpation of the thyroid gland for enlargement, a standard part of the physical examination, especially for senior cats. There are two thyroid palpation techniques for cats described in the literature. The classic technique has the cat in a sitting position with the neck extended. Another technique has the cat standing with the head elevated and turned to one side. The diagnostic value of these techniques has not been compared. In this prospective study, 9 client-owned hyperthyroid cats and 10 healthy control cats were examined twice by 3 blind-folded clinicians using each palpation technique. A score from 1 to 6 was assigned to thyroid gland size each time. After clipping the hair of the ventral neck region, a final palpation session was performed, followed by ultrasonography of the gland. The classic palpation technique led to smaller within- and between-examiner differences. Clipping the hair coat did not make a significant difference. While both thyroid palpation techniques had good within- and between-examiner results, the investigators concluded that the classic palpation technique is preferred.
>> PubMed Abstract

Related Articles:
Norsworthy, G., V. Adams, et al. (2002). "Relationship between semi-quantitative thyroid gland palpation and total thyroxine concentration in cats with an without hyperadrenocorticism." J Fel Med Surg 4(3): 139.
>> PubMed Abstract

Norsworthy, G., V. Adams, et al. (2002). "Palpable thyroid and parathyroid nodules in asymptomatic cats." J Fel Med Surg 4(3): 145.
>> PubMed Abstract

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Diagnosis of Hyperthyroidism in Cats with Kidney Disease

Wakeling, J., K. Moore, et al. (2008). "Diagnosis of hyperthyroidism in cats with mild chronic kidney disease." Journal of Small Animal Practice 49(6): 287-294.


It is a well known phenomenon that hyperthyroid cats with concurrent non-thyroidal illness, such as chronic kidney disease (CKD), may have total thyroxine concentrations within the normal reference range. This causes a diagnostic dilemma. The objective of this study was to determine total thyroxine, free thyroxine and/or thyroid-stimulating hormone concentrations in cats with mild CKD. Three groups of cats were included: 16 cats with CKD and clinical signs compatible with hyperthyroidism but total thyroxine within the reference range (these cats were confirmed with hyperthyroidism at a later date); 20 cats with CKD and no signs of hyperthyroidism; 20 clinically healthy senior cats (over 8 years of age). Four of the 20 cats with CKD had free thyroxine concentrations that were borderline or high. Of the 16 cats with hyperthyroidism and CKD, free thyroxine was high in 15/16 cats and thyroid-stimulating hormone was low in all cats. The researchers conclude that the combined measurement of free thyroxine with total thyroxine or thyroid-stimulating hormone may be of merit in the diagnosis of hyperthyroidism in cats with chronic kidney disease.
>> PubMed abstract


Related articles:
Langston, C. E. and N. J. Reine (2006). "Hyperthyroidism and the kidney." Clin Tech Small Anim Pract 21(1): 17-21.
>> PubMed abstract


More on cat health: Winn Feline Foundation Library

Wakeling, J., K. Moore, et al. (2008). "Diagnosis of hyperthyroidism in cats with mild chronic kidney disease." Journal of Small Animal Practice 49(6): 287-294.


It is a well known phenomenon that hyperthyroid cats with concurrent non-thyroidal illness, such as chronic kidney disease (CKD), may have total thyroxine concentrations within the normal reference range. This causes a diagnostic dilemma. The objective of this study was to determine total thyroxine, free thyroxine and/or thyroid-stimulating hormone concentrations in cats with mild CKD. Three groups of cats were included: 16 cats with CKD and clinical signs compatible with hyperthyroidism but total thyroxine within the reference range (these cats were confirmed with hyperthyroidism at a later date); 20 cats with CKD and no signs of hyperthyroidism; 20 clinically healthy senior cats (over 8 years of age). Four of the 20 cats with CKD had free thyroxine concentrations that were borderline or high. Of the 16 cats with hyperthyroidism and CKD, free thyroxine was high in 15/16 cats and thyroid-stimulating hormone was low in all cats. The researchers conclude that the combined measurement of free thyroxine with total thyroxine or thyroid-stimulating hormone may be of merit in the diagnosis of hyperthyroidism in cats with chronic kidney disease.
>> PubMed abstract


Related articles:
Langston, C. E. and N. J. Reine (2006). "Hyperthyroidism and the kidney." Clin Tech Small Anim Pract 21(1): 17-21.
>> PubMed abstract


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Carbimazole for Feline Hyperthyroidism

Frenais, R., S. Burgaud, et al. (2008). "Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats." Journal of Veterinary Pharmacology and Therapeutics 31(3): 213-219.


Carbimazole is a common oral treatment for feline hyperthyroidism, although not in North America. Carbimazole is a prodrug, as it is converted to methimazole after metabolism. Methimazole reduces production of the thyroid hormones, T3 and T4. The pharmacokinetics of methimazole was investigated in healthy cats following oral administration of 15 mg of carbimazole as a newly available controlled-release tablet (Vidalta®, Intervet). Methimazole levels were sustained and without a peak when compared to dosing with conventional carbimazole tablets. Repeated oral dosing for 13 days did not lead to accumulation of methimazole in plasma. Absorption of carbimazole was improved when administered with food. The relative oral bioavailability of methimazole following administration of the controlled-release tablets was similar to that of a conventional release formulation (83 ± 21%). The pharmacokinetics of this controlled-release formulation of carbimazole supports its use as a once daily treatment (both as a starting dose and for maintenance therapy) for cats with hyperthyroidism.
>> PubMed abstract


Related articles:
Bucknell, D. G. (2000). "Feline hyperthyroidism: spectrum of clinical presentions and response to carbimazole therapy." Aust Vet J 78(7): 462-5.
Free, full text article


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Frenais, R., S. Burgaud, et al. (2008). "Pharmacokinetics of controlled-release carbimazole tablets support once daily dosing in cats." Journal of Veterinary Pharmacology and Therapeutics 31(3): 213-219.


Carbimazole is a common oral treatment for feline hyperthyroidism, although not in North America. Carbimazole is a prodrug, as it is converted to methimazole after metabolism. Methimazole reduces production of the thyroid hormones, T3 and T4. The pharmacokinetics of methimazole was investigated in healthy cats following oral administration of 15 mg of carbimazole as a newly available controlled-release tablet (Vidalta®, Intervet). Methimazole levels were sustained and without a peak when compared to dosing with conventional carbimazole tablets. Repeated oral dosing for 13 days did not lead to accumulation of methimazole in plasma. Absorption of carbimazole was improved when administered with food. The relative oral bioavailability of methimazole following administration of the controlled-release tablets was similar to that of a conventional release formulation (83 ± 21%). The pharmacokinetics of this controlled-release formulation of carbimazole supports its use as a once daily treatment (both as a starting dose and for maintenance therapy) for cats with hyperthyroidism.
>> PubMed abstract


Related articles:
Bucknell, D. G. (2000). "Feline hyperthyroidism: spectrum of clinical presentions and response to carbimazole therapy." Aust Vet J 78(7): 462-5.
Free, full text article


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Kidney Insufficiency After Treatment for Feline Hyperthyroidism

Riensche, M. R., T. K. Graves, et al. (2008). "An investigation of predictors of renal insufficiency following treatment of hyperthyroidism in cats." J Feline Med Surg 10(2): 160-6.

Renal insufficiency is a common finding in older cats, affecting about 30% of cats over age 15. Hyperthyroidism is the most common endocrine disorder in cats, and it appears to be increasing in incidence over time. Hyperthyroidism can mask underlying renal disease by causing an increase in the glomerular filtration rate (GFR). Treatment of hyperthyroidism leads to a decrease in GFR and an increase in blood urea nitrogen (BUN). Different treatments exist for hyperthyroidism in cats, including reversible (methimazole) and irreversible (thyroidectomy, radioiodine) options. The ability to predict which cats will develop renal insufficiency after treatment for hyperthyroidism would help guide treatment decisions. The purpose of this retrospective study was to determine if routine pre-treatment clinical data can be used to predict the development of overt renal insufficiency following treatment of feline hyperthyroidism. Medical records were reviewed for 39 nonazotemic cats undergoing treatment for hyperthyroidism at the College of Veterinary Medicine, University of Illinois. The records were reviewed for for signalment, clinical signs, and serum biochemical, hematologic and urinalysis findings before and after treatment for hyperthyroidism. Cats that developed renal insufficiency within 6 months after treatment (n=20) were compared to cats that did not (n=19). No significant differences could be detected between the groups with respect to the parameters measured. The study suggests that the results of routine pre-treatment clinical data cannot be used to predict renal function after treatment for hyperthyroidism, and that a trial of methimazole therapy is indicated before choosing irreversible treatment such as radioiodine.
>> PubMed abstract

Related articles:
Boag, A. K., R. Neiger, et al. (2007). "Changes in the glomerular filtration rate of 27 cats with hyperthyroidism after treatment with radioactive iodine." Vet Rec 161(21): 711-5.
>> PubMed abstract

More on cat health: Winn Feline Foundation Library

Riensche, M. R., T. K. Graves, et al. (2008). "An investigation of predictors of renal insufficiency following treatment of hyperthyroidism in cats." J Feline Med Surg 10(2): 160-6.

Renal insufficiency is a common finding in older cats, affecting about 30% of cats over age 15. Hyperthyroidism is the most common endocrine disorder in cats, and it appears to be increasing in incidence over time. Hyperthyroidism can mask underlying renal disease by causing an increase in the glomerular filtration rate (GFR). Treatment of hyperthyroidism leads to a decrease in GFR and an increase in blood urea nitrogen (BUN). Different treatments exist for hyperthyroidism in cats, including reversible (methimazole) and irreversible (thyroidectomy, radioiodine) options. The ability to predict which cats will develop renal insufficiency after treatment for hyperthyroidism would help guide treatment decisions. The purpose of this retrospective study was to determine if routine pre-treatment clinical data can be used to predict the development of overt renal insufficiency following treatment of feline hyperthyroidism. Medical records were reviewed for 39 nonazotemic cats undergoing treatment for hyperthyroidism at the College of Veterinary Medicine, University of Illinois. The records were reviewed for for signalment, clinical signs, and serum biochemical, hematologic and urinalysis findings before and after treatment for hyperthyroidism. Cats that developed renal insufficiency within 6 months after treatment (n=20) were compared to cats that did not (n=19). No significant differences could be detected between the groups with respect to the parameters measured. The study suggests that the results of routine pre-treatment clinical data cannot be used to predict renal function after treatment for hyperthyroidism, and that a trial of methimazole therapy is indicated before choosing irreversible treatment such as radioiodine.
>> PubMed abstract

Related articles:
Boag, A. K., R. Neiger, et al. (2007). "Changes in the glomerular filtration rate of 27 cats with hyperthyroidism after treatment with radioactive iodine." Vet Rec 161(21): 711-5.
>> PubMed abstract

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Liver Function and Hyperthyroidism in Cats

Berent, A. C., K. J. Drobatz, et al. (2007). Liver function in cats with hyperthyroidism before and after 131I therapy. J Vet Intern Med 21(6): 1217-23.

Hyperthyroidism is a common endocrine disease of senior cats, and many patients have changes in liver enzymes and other markers of liver function at the time of diagnosis. The clinical significance of these markers of liver damage is unknown. In this study, the liver function of 19 cats with naturally occurring hyperthyroidism was evaluated before and after I-131 therapy. The majority of the cats (15/19) had significant increases in at least one liver enzyme, yet functional testing was normal. All hyperthyroid cats had normal livers on ultrasound examination. All cats responded to treatment with I-131 and all changes in liver enzymes returned to normal. This study supports the conclusion that investigation for liver disease is unnecessary in most cats with hyperthyroidism.
>> PubMed abstract

Related articles:
Archer, F. J. and S. M. Taylor (1996). Alkaline phosphatase bone isoenzyme and osteocalcin in the serum of hyperthyroid cats. Can Vet J 37(12): 735-9.
[Free full text article]

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Berent, A. C., K. J. Drobatz, et al. (2007). Liver function in cats with hyperthyroidism before and after 131I therapy. J Vet Intern Med 21(6): 1217-23.

Hyperthyroidism is a common endocrine disease of senior cats, and many patients have changes in liver enzymes and other markers of liver function at the time of diagnosis. The clinical significance of these markers of liver damage is unknown. In this study, the liver function of 19 cats with naturally occurring hyperthyroidism was evaluated before and after I-131 therapy. The majority of the cats (15/19) had significant increases in at least one liver enzyme, yet functional testing was normal. All hyperthyroid cats had normal livers on ultrasound examination. All cats responded to treatment with I-131 and all changes in liver enzymes returned to normal. This study supports the conclusion that investigation for liver disease is unnecessary in most cats with hyperthyroidism.
>> PubMed abstract

Related articles:
Archer, F. J. and S. M. Taylor (1996). Alkaline phosphatase bone isoenzyme and osteocalcin in the serum of hyperthyroid cats. Can Vet J 37(12): 735-9.
[Free full text article]

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Efficacy of Transdermal Atenolol for Cats

Macgregor, J. M., J. E. Rush, et al. (2008). "Comparison of pharmacodynamic variables following oral versus transdermal administration of atenolol to healthy cats." Am J Vet Res 69(1): 39-44.

Atenolol is often prescribed for cats with certain types of heart disease, most notably some forms of hypertrophic cardiomyopathy. The drug is typically prescribed as 1/4 of a 25 mg tablet every 12 hours. Long term daily administration of oral medication may be very difficult for some owners to achieve. In recent years, there has been great interest in transdermal formulations of medication for cats. Few studies have reported on the efficacy of transdermal gel medications for cats, and of those that have been published the results are not always promising. In this project, atenolol was administered to 7 healthy cats, either orally or as a transdermal gel. Blood levels of atenolol were tested to determine efficacy of the route of administration. The difference between the two routes of administration was significant, with transdermal atenolol providing lower and inconsistent blood levels compared to oral administration.
>> PubMed abstract

Related articles:
Helms, S. R. (2007). "Treatment of feline hypertension with transdermal amlodipine: a pilot study." J Am Anim Hosp Assoc 43(3): 149-156.

Lecuyer, M., S. Prini, et al. (2006). "Clinical efficacy and safety of transdermal methimazole in the treatment of feline hyperthyroidism." Can Vet J 47(2): 131-5. [Free full text article]

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Macgregor, J. M., J. E. Rush, et al. (2008). "Comparison of pharmacodynamic variables following oral versus transdermal administration of atenolol to healthy cats." Am J Vet Res 69(1): 39-44.

Atenolol is often prescribed for cats with certain types of heart disease, most notably some forms of hypertrophic cardiomyopathy. The drug is typically prescribed as 1/4 of a 25 mg tablet every 12 hours. Long term daily administration of oral medication may be very difficult for some owners to achieve. In recent years, there has been great interest in transdermal formulations of medication for cats. Few studies have reported on the efficacy of transdermal gel medications for cats, and of those that have been published the results are not always promising. In this project, atenolol was administered to 7 healthy cats, either orally or as a transdermal gel. Blood levels of atenolol were tested to determine efficacy of the route of administration. The difference between the two routes of administration was significant, with transdermal atenolol providing lower and inconsistent blood levels compared to oral administration.
>> PubMed abstract

Related articles:
Helms, S. R. (2007). "Treatment of feline hypertension with transdermal amlodipine: a pilot study." J Am Anim Hosp Assoc 43(3): 149-156.

Lecuyer, M., S. Prini, et al. (2006). "Clinical efficacy and safety of transdermal methimazole in the treatment of feline hyperthyroidism." Can Vet J 47(2): 131-5. [Free full text article]

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