315 - Musculocutaneous mononeuropathy following penetrating shoulder injury

Case Diagnosis: Musculocutaneous mononeuropathy

Case Description: A 31 year old male presented with a left shoulder stab wound and required surgical repair of the axillary artery and vein. Ten weeks post-injury he was referred by surgery for EMG to evaluate for possible causes of left arm weakness and forearm numbness. Physical exam was notable for left biceps atrophy, marked left elbow flexion weakness with no obvious contraction of the left biceps, and diminished sensation to light touch in the lateral forearm.



Motor nerve conduction studies were significant for an absent left musculocutaneous nerve response. A left lateral antebrachial cutaneous nerve response was also unobtainable. Needle testing displayed electrical evidence of denervation of the left biceps muscle with no voluntary motor unit potentials noted. Additional electrical testing isolated the injury to the left musculocutaneous nerve, with no electrical evidence of a brachial plexopathy or cervical radiculopathy. Patient subsequently underwent a distal nerve transfer via the Oberlin Procedure.

Discussions: Isolated musculocutaneous nerve injury is rare due to the nerve’s limited course and deep location within the shoulder and arm. Trauma and surgery are the most common causes of musculocutaneous neuropathy. Pain and sensory disturbances are reported to be more common than weakness in the literature, likely due to redundancy in elbow flexors. The Oberlin procedure is a distal nerve transfer utilizing a graft of fascicles from the ulnar nerves to the biceps and the median nerve to the brachialis to restore elbow flexion. Outcomes are best when performed within one year of injury.

Conclusions: Despite its rarity, physiatrists should be comfortable accurately identifying musculocutaneous mononeuropathy and ruling out other diagnoses with electrodiagnostic testing. Prompt recognition of this condition allows for the most effective rehab and surgical treatment.