The course of untreated mild T3 toxicosis.

A selected group of 12 patients with mild T3 toxicosis, has been assessed without treatment during a period of from seven to 38 months. Progression to typical hyperthyroidism with combined T4 and T3 excess occurred in one case of solitary toxic adenoma, while a spontaneous remission with return of the thyrotropin response to thyrotropin-releasing hormone occurred in one patient with a diffuse goitre. The other 10 patients showed persistence of isolated high levels of T3 without clinical or biochemical progression. These findings suggest that progression to typical hyperthyroidism is infrequent in mild T3 toxicosis. Because of the possible adverse effects of therapy it may be appropriate to observe, rather than treat, some patients with mild clinical and biochemical features of hyperthyroidism.