Intramuscular myxoma of the supinator muscle causing posterior interosseous nerve palsy: a case report and review of literature

Intramuscular myxomas (IMMs) are rare benign tumors of large skeletal muscles, most often in the thigh, shoulder, or gluteal region. Forearm involvement, especially in the supinator, is exceptionally uncommon and may cause nerve compression when near neurovascular structures. We report a rare case of a 47-year-old woman presenting with a gradually enlarging, painless mass in the dorsal aspect of the proximal left forearm and associated wrist drop. Imaging revealed a well-circumscribed, mucinous lesion within the supinator muscle. Histopathological evaluation confirmed the diagnosis of an IMM. The tumor was surgically excised, with intraoperative findings revealing compression of the posterior interosseous nerve. Postoperatively, the patient demonstrated progressive improvement in wrist extension without evidence of recurrence. This case highlights a rare presentation of IMM causing posterior interosseous nerve compression and wrist drop. Marginal excision is often curative given its benign nature. IMM should be considered in painless, slow-growing masses with motor deficits.