Isolated Musculocutaneous Nerve Injury in a Professional Baseball Player: A Case Report

INTRODUCTION: Musculocutaneous nerve lesion in a throwing athlete is a rare condition. We report the case of a professional baseball pitcher with an isolated musculocutaneous nerve lesion that occurred during a pitching motion. CASE PRESENTATION: The patient had radiating pain in the upper arm and weakness of elbow flexion. Physical examination revealed flaccid paralysis of the biceps brachii muscle and paresthesia in the right lateral forearm. Musculocutaneous nerve injury was suspected. Because some signs of recovery were observed within a few days, the patient received non-operative management. Nerve conduction studies at 2 weeks after the injury showed low-amplitude compound muscle action potential of the right biceps brachii muscle by stimulation of the musculocutaneous nerve. Needle electromyography showed markedly reduced motor unit potential recruitment in the biceps brachii muscle. He was diagnosed as having isolated musculocutaneous nerve injury. At 2 months after the injury, the muscle contraction and strength of the biceps brachii muscle improved. At 7 months after the injury, muscle weakness was fully recovered. His pitching ability returned to that of a competitive player. CONCLUSION: Because the neuroparalysis was incomplete and began to recover within a few days, we considered the pathology of this injury to be incomplete axonotmesis, which was successfully treated conservatively.