Case Series: Minocycline-Associated Thyroiditis

Introduction: Minocycline, a member of the tetracycline class of antibiotics, has been associated with benign thyroid pigmentation but reports of thyroid dysfunction are sparse.

Methods: Cases were selected via an inquiry of the electronic medical records for patients with thyroid dysfunction and the use of a tetracycline antibiotic. Non-autoimmune thyroiditis was defined as abnormally low or suppressed thyroid-stimulating hormone (TSH, <0.3 µIU/mL), elevated free thyroxine or total thyroxine, and undetectable antithyroid antibodies.

Results: Nine cases of thyroiditis without autoimmunity were identified out of 423 reviewed patients. Cases of thyroiditis occurred in adolescents ages 14-17 years who had been taking minocycline for 6 months to 4 years. In all cases, minocycline was prescribed for the treatment of acne. Four of the 9 received treatment for thyrotoxicosis with a β-blocker (in 3 cases) and/or antithyroid drug (in 2 cases). Thyroiditis was symptomatic in all but one individual who presented with painless goiter. All thyroiditis was transient and resolved after a median of 4.5 months (range 2-5 months). In one case, thyroiditis was followed by transient hypothyroidism.

Discussion: Minocycline is known to cause thyroid abnormalities, although it has not been definitively linked to thyroid dysfunction. Here, we report 9 cases of non-autoimmune thyroiditis in adolescents receiving minocycline for acne. We recommend that minocycline exposure be considered in the differential diagnosis for thyroiditis and that patients receiving minocycline be counseled regarding the risk of thyroid dysfunction.