A Case Report on Methimazole Induced Anti-Thyroid Arthritis Syndrome: A Rare Drug Induced Migratory Polyarthritis

Antithyroid drugs (ATD's) are widely used as the first line treatment option for the management of hyperthyroidism, especially for patients with Graves’ disease. They are classified into thionamide (Methimazole, Carbimazole and Propylthiouracil) and Non-thionamide (Iodine containing compounds) ATD's. These drugs are associated with various types of adverse effects ranging from mild to potentially life threatening. Antithyroid arthritis syndome (AAS) is one of the major and uncommon side effects of ATD therapy requiring immediate drug discontinuation and hospitalization presents itself with myalgia, arthralgia and arthritis along with fever and rash of varying severity and non-specific laboratory findings, making its diagnosis and management clinically challenging. Here we report the case of 32 year old female with Graves’ disease who experienced severe migratory polyarthritis after the initiation of methimazole therapy. Her symptoms started to disappear after the prompt withdrawal of methimazole. We also concluded that this adverse effect of ATD's might not be dose dependent by comparing our case with 6 other case reports of AAS. Here our objective is to raise awareness among the clinicians regarding the differential diagnosis and management of this major, uncommon and potentially life threatening adverse effect of ATD therapy.