Endocrine Abstracts

Antithyroid Arthritis Syndrome (AAS) is a rare but serious side effect of antithyroid drugs (ATDs) which can present symptoms that severely impact quality of life, such as severe myalgia and arthralgia, shortly after starting the culprit medication. It can be difficult to differentiate from other arthritis causes, and its immune-mediated pathophysiology is not fully understood. This report discusses a patient who developed AAS following antithyroid therapy and was difficult to manage due to patient very keen to have children.

Case Presentation: 31 years old Japanese women was previously diagnosed with thyrotoxicosis and confirmed Graves’ disease in Japan and started on Carbimazole 20 mg daily. The patient visited our endocrine clinic as she was eager to conceive. She was advised to switch to Propylthiouracil. Shortly after starting Propylthiouracil, she reported symmetrical joint pain and swelling particularly of her hands, with minimal lower limb involvement, particularly the knees. AAS was diagnosed due to the timing of arthritis onset after Propylthiouracil initiation and exclusion of other causes. Anti-neutrophil cytoplasmic antibody (ANCA) negativity is needed to differentiate from antithyroid agent-induced ANCA-associated vasculitis, which shows arthritis similar to AAS

Management and Outcome: Propylthiouracil was disco¬ntinued, Carbimazole restarted and alternative treatment options, including surgery and radioactive iodine, were discussed. The patient’s joint pain and swelling significantly improved after stopping the culprit medication. However, due to patient wish for pregnancy, Propylthiouracil was restarted and she was complained again of joint pain. Patient struggled during first trimester but then as soon as was safe – was changed back to Carbimazole.

Conclusion: This case highlights the need to recognize AAS. High vigilance required in patients of Japanese origin who complain of polyarthritis on ATDs. Early identification and cessation of the drug is essential for complete resolution of symptoms.