Background: Thionamides are the main therapeutic arsenal for treating hyperthyroidism. Perhaps the
first case of a patient who developed a transient pituitary hyperthyroidism after discontinuation of a lengthy intake of a thionamide is reported.
Case Report: A 48-year-old woman presented with menstrual irregularities when hypothyroidism with pituitary enlargement was detected. She had been undergoing treatment with methimazole for Graves’s
hyperthyroidism since the age of 34. Three months after discontinuation of methimazole she presented
with clinical and laboratory evidence of thyrotoxicosis, with elevated thyroid-stimulating
hormone (TSH) levels and blunted response to thyrotropin releasing hormone (TRH). This secondary
hyperthyroidism was self-limited and resolved a few months later.
Conclusions: Chronic primary hypothyroidism caused by lengthy use of thionamides can result in pituitary hyperplasia and transient thyrotrope dysfunction.

Keywords: Triiodothyronine - blood, Time Factors, Thyroxine - blood, Thyrotropin - blood, Thyrotoxicosis - diagnosis, Thyroid Gland - ultrasonography, Propranolol - therapeutic use, Anti-Anxiety Agents - therapeutic use, Methimazole - therapeutic use, Hypothyroidism - drug therapy, Hyperthyroidism - etiology, Follow-Up Studies, Chronic Disease