Dietary Management of Hyperthyroidism in a Dog

An 8 yr old female spayed golden retriever presented for a routine exam during which ventral cervical soft tissue masses were identified. History included weight loss, increased activity and appetite, gagging, and occasional diarrhea. Exam findings included a body condition score of 4/9 and palpable ventral cervical nodules. A serum thyroxine (T4) value was 8.0 ug/dL (normal = 0.8-3.5ug/dL). Doppler systolic blood pressure readings ranged from 200-210 mmHg (normal systolic blood pressure <150 mmHg). The diagnosis was hyperthyroidism due to active thyroid masses. Due to financial constraints, the owner elected conservative management. Initial treatment with methimazole resulted in a decreased T4 value of 5.0 ug/dL at approximately 4 mo after initiation of treatment. A commercially available iodine-restricted feline diet was fed and this resulted in further reduction in serum T4 levels, improved sleeping cycles, reduced anxiety, and reduced systolic blood pressure. A temporary suspension of iodine-restricted feline diet for 2 mo resulted in increases in serum T4 concentrations, which, subsequently, decreased with re-introduction of the diet. Roughly 10 mo after initiation of the therapeutic diet and 16 mo after intial diagnosis, the dog remains relatively normal clinically despite active growing cervical masses with T4 concentration of 2.3 ug/dL.