Hemiaplasia of the thyroid with thyrotoxicosis

Four patients with hemiaplasia of the thyroid gland presented with thyrotoxicosis. Each patient was noted to have unilateral goiter without palpable thyroid tissue on the contralateral side. Investigation of these patients included measurements of serum L-T4, T3, thyroglobulin, thyroid microsomal antibody, long acting thyroid stimulator (LATS), and long acting thyroid stimulator protector (LATS-P). In addition, an 131I thyroid scan was performed on each patient and was repeated after TSH administration (TSH stimulation test). Three patients underwent surgery; information from the remaining patient was obtained from postmortem examination. In three patients, LATS and LATS-P were undetected, and these subjects were found to have adenomas. LATS-P, without LATS, was detected in the remaining patient, and she was found to have diffuse hyperplasia. From our cases as well as a search of the world literature, three points arise. 1) Hemiaplasia is found only when attention is drawn to the thyroid gland through some other abnormality, e.g. thyrotoxicosis or goiter. The true incidence of hemiaplasia, therefore, is unknown. 2) A TSH stimulation test is essential to differentiate hemiaplasia from a hot nodule with contralateral thyroid suppression. 3) The measurement of thyroid-stimulating immunoglobulins may be helpful in distinguishing toxic adenoma from Graves' disease without exophthalmos.