We report an isolated musculocutaneous neuropathy caused by a proximal hume
ral osteochondroma that became symptomatic after the patient played recreat
ional basketball. Lesion resection resulted in complete deficit resolution.
Mass lesions involving the musculocutaneous nerve should be considered in
patients with atraumatic, isolated musculocutaneous neuropathies that are r
ecurrent or fail to recover, even in the setting of strenuous exercise.