Thirty-five cases of transient hyperthyroidism.

Over a 7-year period transient hyperthyroidism was diagnosed in 35 patients seen in a consulting practice in a community hospital. The patients were followed up for an average of 15 months. Initially all of them had biochemical evidence of hyperthyroidism but a very low 24-hour uptake of radioiodine. The hyperthyroid phase was short, and there were no relapses. Seventeen patients subsequently became hypothyroid; this phase, too, was almost always transient. The clinical course of the disease in the 11 women who became hyperthyroid within 6 months after giving birth was similar to that experienced by the other patients, but of the 11 who had increased titres of antimicrosomal antibodies a significantly greater proportion (73%) showed at least transient evidence of hypothyroidism; 1 patient remained frankly hypothyroid for a year. Transient hyperthyroidism can be distinguished from Graves' disease only if the uptake of radioiodine is measured. It is important to make this distinction, as transient hyperthyroidism can be managed safely and symptomatically with beta-blockers alone. The propensity of this disease for the postpartum period and the high proportion of patients with antithyroid antibodies suggest an autoimmune cause.