THE PREVALENCE OF HYPERTENSION IN HYPERTHYROID CATS AT DIAGNOSIS AND FOLLOWING TREATMENT.
HM Syme, J Elliott.
Journal of Veterinary Internal Medicine 17: 754, 2003 (research abstract)

Hyperthyroidism has been reported as an important cause of hypertension in the cat. However systematic studies of blood pressure in hyperthyroid cats have not been reported and, in large case series, signs consistent with hypertensive retinopathy/choroidopathy have been noted infrequently. The aim of this study was to determine the prevalence of hypertension in hyperthyroid cats at the time of diagnosis, and following initial treatment. Blood pressure measurements were made on all cats diagnosed with hyperthyroidism by the authors over a 42-month period. Hyperthyroidism was diagnosed when total thyroxine measurements exceeded the laboratory reference range (.55 nmol/l). Hypertension was diagnosed if systolic blood pressure (SBP), measured by a Doppler method, was .175 mm Hg and consistent ocular lesions were present, or if the SBP was .175 mm Hg on two or more occasions. SBP measurements were compared before and after successful induction of euthyroidism (due to carbimazole treatment or surgical thyroidectomy) by a paired student t-test. Additionally, the number of cats that developed hypertension in the first 6 months of treatment was recorded. One hundred cats were sequentially enrolled into the study; of these 3 were already receiving amlodipine therapy for treatment of hypertension (diagnosed 203, 357 and 826 days prior to the diagnosis of hyperthyroidism) and 9 were diagnosed with hypertension simultaneously. Five of the hypertensive cats had ocular lesions. SBP decreased significantly following initial treatment for hyperthyroidism (from 144.9 6 16.8 to 139.8 6 21.3 mm Hg, n 5 59, P 5 0.04, treatment interval 32 6 20 days) but during the initial 6 months of treatment hypertension developed in 9/40 (22.5%) of the initially normotensive cats in which hyperthyroidism was well controlled. 2003 ESVIM Abstracts 755 In conclusion, severe hypertension is relatively uncommon in cats at the time of diagnosis of hyperthyroidism. However, a significant number of cats will develop hypertension following the induction of euthyroidism. It is, therefore, important to monitor cats’ blood pressure following initiation of therapy.