Toxic Graves' disease with thyroid hemiagenesis: diagnosis using thyroid-stimulating immunoglobulin measurements.

Two patients with hemiagenesis of the thyroid gland experienced thyrotoxicosis. They constituted 1.1% of our clinic's total population of 178 thyrotoxic patients treated in the years 1986-1990 and 1.7% of 120 patients with thyrotoxic Graves' disease encountered during that period. The diagnosis was made on the basis of unilateral homogeneous 99mTcO4 uptake on thyroid scan, no change in the scan after both cessation of propylthiouracil (PTU) treatment for 4 days and TSH stimulation test, and high thyroid-stimulating immunoglobulin (TSI) levels. Both patients went into remission after PTU treatment, and TSI levels returned to normal. The diagnosis of toxic Graves' disease with thyroid hemiagenesis was, therefore, made. This combination is rare but important to recognize because treatment as well as prognosis might be different from that of toxic adenoma.