Posterior Interosseous Nerve Palsy Induced by Ganglion Cyst: A Case Report

Posterior interosseous nerve (PIN) palsy is a rare condition that causes motor deficits without sensory loss, often due to trauma, compression, or inflammation. One possible cause is compression by a ganglion cyst, a benign lesion often arising from tendon sheaths or joint capsules, particularly near the elbow's arcade of Frohse. This report describes the rare diagnosis and treatment of a PIN palsy secondary to a ganglion cyst in an 81-year-old man. Electromyography (EMG) confirmed PIN dysfunction, and imaging identified a 13mm ganglion cyst at the arcade of Frohse compressing the nerve. Surgical decompression and cyst excision resulted in progressive motor recovery, with complete resolution of symptoms by six months. This case highlights the importance of considering ganglion cysts in cases of non-traumatic PIN palsy. Early recognition and surgical intervention can facilitate full neurologic recovery.