1508 - Recognizing Spinal Accessory Neuropathy in Patients with Shoulder Pain and Scapular Winging: Importance of Electrodiagnosis

Case Diagnosis: Incomplete right spinal accessory neuropathy confirmed by electrodiagnosis.

Case Description:

A 76-year-old male presented with right shoulder pain, weakness, and scapular winging. Seven months before presentation, he underwent carotid endarterectomy and reported transient right neck numbness, which gradually improved. Two months before, he fell onto the right shoulder and noticed pain, weakness, and difficulty with overhead activities.

Exam showed atrophy of the right sternocleidomastoid and trapezius with lateral scapular winging. Trapezius weakness was evident while distal strength, reflexes, and sensation were preserved except for an area of numbness near the AC joint. Electrodiagnostic testing revealed low amplitude and prolonged onset latency of the right spinal accessory motor response compared with the left. Bilateral long thoracic and right ulnar motor conduction studies were normal, as were radial and ulnar sensory studies. Needle EMG examination demonstrated fibrillation potentials in the right trapezius with absent voluntary motor unit action potentials. The electrophysiologic study was consistent with incomplete right spinal accessory neuropathy (SAN).

Discussions:

The spinal accessory nerve is vulnerable to injury due to its superficial course in the posterior cervical triangle. Symptoms may overlap with rotator cuff and shoulder pathology. In addition, distinguishing medial and lateral scapular winging can be clinically challenging. Electrophysiologic study is essential for confirming diagnosis and excluding brachial plexus or mononeuropathy involvement. In this case, both carotid endarterectomy and subsequent trauma are plausible mechanisms.

Conclusions: This case highlights that clinicians should maintain a high suspicion for SAN in a patient with scapular winging after carotid surgery and trauma. Prompt recognition and appropriate workup with electrophysiologic study is essential to confirm SAN, to exclude alternative diagnoses, to clarify prognosis, and to guide rehabilitation programs.