Compensated, goitrous hypothyroidism in rhesus macaques.

Bilateral cervical masses were observed in two newborn, male, rhesus macaques. The clinical diagnosis was congenital goiter. Thyroid function screening tests revealed that the affected monkeys had normal triiodothyronine levels, low thyroxine values, and elevated thyroid-stimulating hormone levels. Radioactive iodine uptake and perchlorate discharge tests indicated a postorganification defect. A third, male, rhesus macaque, stillborn after a prolonged gestation, also had bilateral cervical masses. Necropsy and histopathology examinations confirmed the masses were enlarged, hyperplastic thyroid glands. Each affected infant had the same parents.