A Case of Unilateral Brachial Plexus Injury Caused by First-Rib Stress Fractures Presenting With an Uncontrollable Involuntary Movement of the Neck.

Stress fracture of the first rib is a rare but an important cause of brachial plexopathy. Here, we describe a patient with a unilateral brachial plexus injury presenting with involuntary neck movements. A 22-year-old man with cervical involuntary movements for 10 months was diagnosed with tardive dyskinesia. After admission, he abruptly noticed that he could not lift his right arm. The electrophysiological study revealed weakness of the right deltoid and brachioradialis, but normal findings in the other muscles innervated by the right C5 segment. Chest computed tomography showed fractures of the first rib on both sides, with callus formation. Based on the involvement of muscles innervated by the right axillary and radial nerves and presence of callus at the first rib, a diagnosis of right posterior cord entrapment was made. In the present case, intermittent strong contraction of muscles due to dyskinesia may have caused the stress fractures.