The early development of transient and permanent hypothyroidism following radioiodine therapy for hyperthyroid Graves' disease.

The outcome in 110 patients first treated with radioiodine (mean dose 6.56 mCi) for hyperthyroid Graves' disease in 1980 was reviewed. In 23% of the patients the disease had not been controlled by the initial dose after 3 months, and 17% were given one or two more doses. Within 2 years 65% of the patients required replacement thyroxine therapy. Although about half of the patients were biochemically hypothyroid 3 months after the last dose of iodine 131, this condition was transient in a third of them; five of these patients even became hyperthyroid again. Patients with transient, as opposed to permanent, hypothyroidism at 3 months tended to be clinically euthyroid but to have residual palpable thyroid tissue and only a modest reduction in the serum thyroxine level. It is therefore recommended that patients not overtly hypothyroid 3 months after treatment with 131I be observed still longer before thyroxine replacement therapy is instituted.