Hypothyroidism is considered to be the most common endocrine disorder in dogs. It is seen mostly in middle-aged dogs in the mid-larger sized breeds. More than 80% of the cases result from autoimmune thyroiditis, which progressively destroys the thyroid gland. The clinical signs are quite variable - some are subtle and may mimic those of other causes2. Therefore, in order to facilitate diagnosis thyroid profile testing should be conducted. TSH, FT4, T4 and other thyroid assays are all useful when used together to assess the thyroid status.
Although hypothyroidism is quite rare in cats, hyperthyroidism is considered the most common feline endocrine disorder. It afflicts primarily middle-aged and older cats. Also called thyrotoxicosis, hyperthyroidism is caused by an increase in production of thyroid hormone from enlarged thyroid glands. In most cases, enlargement of thyroid glands is caused by a tumor called an adenoma, which is non-cancerous. Some rare cases of hyperthyroid disease are caused by malignant tumors known as thyroid adenocarcinomas3.
Increased frequency of diagnosis of feline hyperthyroidism can be attributed to increased clinical awareness of the disease, improved diagnostic testing, an increasing feline population, increased lifespan of pet cats, and the fact that more owners seek veterinary aid for their pets4.
1. 2011-2012 APPA National Pet Owners Survey
2. Veterinary Practice News. www.veterinarypracticenews.com posted April 12, 2011 by W. Jean Dodds, DVM
3. Brochure on Hyperthyroidism in Cats. Prepared b the American Association of Feline Practitioners and the Cornell Feline Health Center, Cornell University, College of Veterinary Medicine 2007
4. Veterinary Clinical pathology clerkship program. www.vet.uga.edu Feline Hyperthyroidism. By Jeff S. Stortz, DVM; Kenneth S. Latimer, DVM, PhD; Heather L. Tarpley, DVM; Bruce E. LeRoy, DVM, PhD, Perry J. Bain, DVM, PhD, T. Michelle Wall, DVM, DACVIM
5. IDEXX Laboratories. Diagnostic Update. March 2011.IDEXX Reference laboratories new Free T4 Test
6. Boretti, FS, Reusch C.E.- Diagnostic specificity of canine thyrotropin in the diagnosis of Hypothyroidism in dogs. EJCAP 2006,16:185-189
7. The Merck Veterinary Manual. © 2011; Merck Sharp & Dohme Corp., a subsidiary of Merck & Co., Inc