T4 toxicosis

Abstract

We have described a 25-year-old man with hyperthyroidism and normal levels of serum T3 and reverse T3, but with abnormalities in serum T4I, T3U, FTI, FT4, and T3 suppression and TRH stimulation tests consistent with the diagnosis of T4 toxicosis. Serum total iodine was elevated several-fold, and the observed response to iodine depletion and loading suggested that the T4 toxicosis in this patient probably resulted from an increased iodine load, with production of T4 preferentially to T3. There appeared to be no evidence of a defect in peripheral conversion of T4 to T3.