Spontaneous hyperthyroidism in an aged male and female Macaca mulatta

A 31-year-old male and a 31-year-old female rhesus monkey developed clinical signs consistent with hyperthryoidism. These included a ravenous appetite, hyperactivity, and accentuated ratchet movement and hand tremors while performing fine motor tasks. Bilaterally enlarged thyroid glands were palpated in both monkeys. A unique clinical finding of the female as the hypertrophic cardiomyopathy. The T3 and T4 levels in the male rhesus were 3.79 ng/ml and 28.20 microg/dl, respectively. T3 and T4 levels in the female were 4.33 ng/ml and 22.2 microg/dl, respectively. A biopsy of the enlarged thyroids demonstrated a typical multinodular goiter with cystic hyperplasia. The female rhesus was successfully treated with methimazole, but the hypertrophic cardiomyopathy did not resolve. The relationship between erythrocytosis and T4 levels common to humans and cats is also evident in the rhesus monkey.