• Annabelle Naman, Brigitte Delemer, Didier Marot, Elise Michelet, Bénédicte Decoudier, and Sara Barraud.
• Centre Hospitalier Universitaire de Reims, Service d'Endocrinologie - Diabète - Nutrition, Reims, France.
• Medicine (Baltimore). 2022 Jul 1; 101 (26): e29690e29690.

RationaleDaily 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 OutcomesAfter 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.LessonsIn 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.Copyright © 2022 the Author(s). Published by Wolters Kluwer Health, Inc.

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