HYPOTHYROIDISM IN DOGS - 66 CASES (1987-1992)

Sixty-six dogs with hypothyroidism were identified from dogs examined over a 5-year period. Hypothyroidism was diagnosed only if the dog had a low, resting serum thyroxine concentration and serum thyroxine conc entration was not higher than the lower limits of the reference range 6 hours after IV administration of bovine thyrotropin. The prevalence of hypothyroidism was 0.2%. Neutering was determined to be the most si gnificant gender-associated risk factor for development of hypothyroid ism. Neutered male and spayed female dogs had a higher relative risk o f developing hypothyroidism than did sexually intact females. Sexually intact females had a lower relative risk. Breeds with a significantly increased risk, compared with other breeds, were the Doberman Pinsche r and Golden Retriever. The most common clinical findings were obesity (41%), seborrhea (39%), alopecia (26%), weakness (21%), lethargy (20% ), bradycardia (14%), and pyoderma (11%). Low voltage R-waves were fou nd on 58% of ECG. Clinicopathologic abnormalities included hypercholes terolemia (73%), nonregenerative anemia (32%), high serum alkaline pho sphatase activity (30%), and high serum creatine kinase activity (18%) . Serum total triiodothyronine concentrations were within reference ra nges in 15% of the hypothyroid dogs. Response to treatment was good in most dogs, but those with severe concurrent disease or neurologic abn ormalities were less likely to respond with complete resolution of cli nical signs.