Treatment-resistant hypothyroidism due to storage of levothyroxine at cold temperature

We present a case of a 37-year-old woman who was referred to the Endocrinology Department of the State Institute for Diabetes and Endocrinology Luiz Capriglione, Rio de Janeiro, Brazil, with persistent hypothyroidism following a total thyroidectomy for multinodular goiter 6 months before the appointment. After the surgery, the patient was prescribed levothyroxine 100μg/day.  Initial blood tests showed increased thyroid stimulating hormone and normal free thyroxine levels. Over the next 2 years, in spite of the patient’s adherence to the treatment and progressive increments in levothyroxine doses, thyroid stimulating hormone levels remained elevated and she developed clinical hypothyroidism. She was then admitted to the hospital for clinical and hormonal stabilization. Upon further investigation, the patient informed that at the beginning of her levothyroxine treatment, she was instructed to store the drug in the refrigerator, at 4°C. Seven days after impatient treatment, thyroid stimulating hormone levels returned to normal and the subject was asymptomatic. After discharge, she was instructed to store the medication properly, at room temperature, and away from heat and light. Two years after discharge, she was still euthyroid and asymptomatic.