<![CDATA[Background: Methimazole is a standard treatment for Graves’ disease and is generally well tolerated. Painful muscle cramps are rarely reported, while thyrotoxicosis itself may cause neuromuscular manifestations. This overlap can make causality difficult to establish. Case presentation: A 38-year-old woman with Graves’ disease and secondary hypertension was treated with Methimazole 20 mg/day and Propranolol 30 mg/day. Approximately one month after treatment initiation, she developed recurrent, sudden, severe, painful muscle cramps triggered by abrupt movements or changes in body position. Episodes lasted less than five minutes and resolved spontaneously without residual weakness. The cramps persisted despite reduction of Methimazole to 10 mg/day. Thyroid function fluctuated during follow-up. In April 2026, FT4 was 13.12 pmol/L and TSHs was 3.59 mIU/L, after which the patient discontinued her medications. The cramps completely resolved and did not recur. Discussion: The temporal relationship and complete resolution after treatment discontinuation suggest a possible association with Methimazole. However, thyrotoxicosis, concomitant medications, absence of rechallenge, and lack of acute creatine kinase or electrolyte measurements limit definitive causal attribution. Conclusion: Painful muscle cramps may represent an uncommon adverse effect associated with Methimazole. Awareness and longitudinal assessment may facilitate recognition and evaluation of similar events.]]>
