Clinical features of primary hyperthyroidism caused by Graves' disease admixed with resistance to thyroid hormone (P453T).

A 34-year-old Japanese woman was referred to the hospital because of general fatigue and palpitations. She was diagnosed as having resistance to thyroid hormone (RTH) and Hashimoto's thyroiditis at the age of 28. She felt general fatigue, palpitations, heat intolerance, and sweating for 6 months. Thyroid function tests demonstrated elevated levels of free triidothyronine (T3) and free thyroxine (T4) that were above detectable ranges and a completely suppressed level of TSH that was below the detectable range. Titers of anti-TSH receptor antibody (TRAb) and thyroid-stimulating antibody (TSAb) were positive. A 20-minute Technetium-m99 pertechnetate thyroid uptake imaging study showed an elevated value of 39.53% and a normal-shaped thyroid gland. These results indicated that Graves' disease (GD) caused primary hyperthyroidism. Pituitary and peripheral tissues responded to the presence of excess thyroid hormone in the patient. Oral administration of methimazole was started and continued for 1 year 10 months, after which it was ceased. Two years after the cessation of methimazole treatment, level of free T4 was elevated compared to reference range, but levels of TSH and free T3 were within normal reference ranges. Titers of TRAb and TSAb remained negative for 2 years. These findings indicated that the patient's GD was in remission. In conclusion, it is difficult to make a differential diagnosis between GD with RTH and GD alone if RTH is not diagnosed before the onset of GD. An antithyroid drug is able to cause the remission of GD with RTH.