THE PATIENT is a 14-year-old girl referred 6 months earlier by her pediatrician for examination of a right thyroid nodule detected during a routine physical examination. She was asymptomatic, and results of the thyroid function studies obtained are shown in the Table. A technetium-99m pertechnetate thyroid scan revealed two "hot" nodules replacing the right lobe of the gland and a normal-sized left lobe with diminished uptake (Figure). Levothyroxine sodium therapy, 100 μg/d, was begun to suppress the nodules. Five months after initiating therapy, further enlargement of the gland was noted, and the dose of levothyroxine sodium was increased to 125 μg/d. Results of thyroid function studies at that time are shown in the Table.
When seen 6 months later by a pediatric endocrinologist, she was asymptomatic except for abdominal cramping and diarrhea related to the increased dose of levothyroxine. Assessment of her medical history was negative, with normal onset