Medullary carcinoma of the thyroid before age 2 years.

An 18-month-old infant was evaluated for medullary thyroid carcinoma (MTC) because of a maternal history of the tumor and the presence of characteristic mucosal abnormalities. Although examination of the thyroid gland was normal, RIA of plasma calcitonin reveled elevated basal levels of the hormone and the patient underwent total thyroidectomy at 23 months of age. Histological examination of the tumor was consistent with the diagnosis f MTC, and this diagnosis was confirmed by immunohistology.