Pseudomalabsorption of levothyroxine: a case report.

A 51-year-old woman who had been treated with levothyroxine sodium because of hypothyroidism after total thyroidectomy for thyroidal cancer was admitted to our hospital for persistent hypothyroidism despite large dose administration of levothyroxine (600 microg/day). The patient complained of severe general fatigue and body weight gain. Free thyroxine, free triiodothyronine and thyrotropin levels were 0.97 ng/dl, 1.55 pg/ml and 24.51 microU/ml, respectively, under oral administration of levothyroxine. Levothyroxine loading test performed by liquid form, pulverized tablets via nasogastric tube and intravenous administration revealed no evidence of malabsorption or metabolic disorder of levothyroxine, although oral intake of tablets was ineffective due to her factitiousness. We report here a possible case of "pseudomalabsorption of levothyroxine" to emphasize the clinical recognition of this disorder in patients with resistant hypothyroidism.