Lugol's solution-induced painless thyroiditis

SummaryLugol’s solution is usually employed for a limited period for thyroidectomy preparation in patients with Graves’ disease and for the control of severe thyrotoxicosis and thyroid storm. We describe a rare case of Lugol’s solution-induced painless thyroiditis. In November 2014, a 59-year-old woman was prescribed Lugol’s solution four drops per day for the alleviation of menopausal symptoms. She was referred to our clinic in June 2015 for fatigue, hair loss, and a 20-lb weight loss without thyroid pain or discomfort. Physical examination revealed a normal thyroid gland. On 7 May 2015, laboratory tests revealed a suppressed thyroid-stimulating hormone (TSH) 0.01 U/L with elevated free T4 3.31 ng/dL (42.54 pmol/L). Repeat testing on 25 May 2015 showed spontaneous normalization of the free thyroid hormone levels with persistently low TSH 0.10 U/L. Following these results, a family physician prescribed methimazole 10 mg PO TID and very soon after, the TSH concentration rose to >100 U/L along with subnormal free T4 and T3 levels. Methimazole was promptly discontinued, namely within 18 days of its initiation. Over the course of the next few months, the patient spontaneously achieved clinical and biochemical euthyroidism. To our knowledge, this is a unique case of painless thyroiditis induced by Lugol’s solution, which has not been reported before. Lugol’s solution is a short-term medication given for the preparation of thyroidectomy in patients with Graves’ disease and for the control of severe thyrotoxicosis. Iodine excess can cause both hyperthyroidism and hypothyroidism. Rarely, Lugol’s solution can cause acute painless thyroiditis.Learning points:Lugol’s solution is used for thyroidectomy preparation in patients with Graves’ disease and for the control of severe thyrotoxicosis and thyroid storm.Iodine excess can cause both hypothyroidism and thyrotoxicosis. Thyroid glands with an underlying pathology are particularly susceptible to the adverse effect of iodine.The prolonged off-label use of Lugol’s solution can be harmful. Rarely, Lugol’s solution can cause acute painful thyroiditis.