Recurrent apathetic hyperthyroidism.

A patient experienced three separate episodes of apathetic hyperthyroidism. Each time, this clinical picture appeared after the patient had been euthyroid for one to three months and within one to three weeks of discontinuing antithyroid drug therapy. This rapid recurrence of apathetic hyperthyroidism represents evidence against the concept that this disorder represents "burnt-out," or exhaustion of, body reserves in long-standing, untreated hyperthyroidism. Initial recognition and diagnosis of thyrotoxicosis was delayed by contamination of her serum from therapeutic radioactive iodine and possible interference with thyroxine radioimmunoassay. The solution to this problem with double isotope counting is discussed.