Euthyroid hyperthyroxinemia and inappropriate secretion of thyrotropin. Recognition and diagnosis

Various disease states associated with euthyroid hyperthyroxinemia and inappropriate thyrotropin secretion are becoming increasingly recognized. These diagnoses were established in six (11%) of 57 patients referred for evaluation of elevated free thyroxine index over an 11-month period. Failure to separate these entities from primary thyrotoxicosis may result in unnecessary thyroid ablative therapy and subsequent clinical confusion. Several illustrative patient summaries are presented to outline an approach to this clinical challenge.