LAUSR

Rationale: Daily oral synthetic levothyroxine (LT4) is the main treatment for hypothyroidism, which, in most cases, allows the regression of symptoms and the normalization of the thyroid function. However, rarely, despite a high dose of oral LT4, hypothyroidism persists and is called refractory hypothyroidism. Intravenous or intramuscular treatment is then often necessary. We report the case of a patient with refractory hypothyroidism successfully treated with subcutaneous LT4. Interventions and outcomes: After 4 weeks of weekly intravenous injections of 200 µg LT4 in complement to the oral treatment, thyroid balance was improved (TSH: 21.8 mIU/L). We tested the replacement of intravenous with subcutaneous injections of LT4 and gradually increased injection frequency from 1 to 3 injections per week (600 µg/week). Simultaneously, oral treatment was gradually tapered off, and within a few months, thyroid function tests were normalized. Two years later, hormone levels remained normal without symptoms of hypothyroidism. The only side effect was a local reaction in the first few weeks of injections, which spontaneously resolved. Lessons: In this case of unexplained oral LT4 malabsorption, subcutaneous injection allowed a self-administrated physiological dose of LT4 3 times weekly. Considering the efficacy of subcutaneous injection of LT4, this treatment could be a safe and easy alternative for patients with malabsorption.