Electrodiagnostic / Neuromuscular Medicine
Joseph Z. Levinson, MD
Resident Physician
University of Virginia, Department of Physical Medicine and Rehabilitation
Charlottesville, Virginia, United States
Talha Ahmad, MD
Resident
Medical College of Wisconsin
Milwaukee, Wisconsin, United States
Kevin Mesina, MD
Fellow Physician
UVA Health
Union, New Jersey, United States
Ryan Lewis, MD
Physician
University of Virginia
Charlottesville, Virginia, United States
Jeffrey G. Jenkins, MD
Professor
University of Virginia
Charlottesville, Virginia, United States
Joseph Z. Levinson, MD
University of Virginia, Department of Physical Medicine and Rehabilitation
Charlottesville, Virginia, United States
Isolated musculocutaneous neuropathy
Case Description:
A 20-year-old male collegiate baseball player presented to the electrodiagnostic laboratory with two months of anterolateral right forearm numbness and paresthesia and subjective right elbow flexion weakness. Symptoms began after a baseball pitch in which his head and neck were laterally flexed away from the right throwing arm. Physical examination revealed mild weakness in elbow flexion on the right and otherwise full strength. MRI and diagnostic ultrasound of the right brachial plexus was normal.
Discussions:
Initial electrodiagnostic evaluation was notable for an absent right lateral antebrachial cutaneous (LAC) sensory nerve action potential (SNAP). Needle electromyography (EMG) demonstrated florid positive sharp waves and reduced motor recruitment in the right biceps brachii, consistent with a subacute right musculocutaneous neuropathy.
Repeat evaluation was ordered to assess for interval improvement six weeks later. Right LAC SNAP was again absent. Needle EMG examination demonstrated fibrillation potentials and enlarged and polyphasic motor unit action potentials in the right biceps and brachialis, evidence of subtle interval improvement with partial reinnervation via axon terminal collateral sprouting.
Given his improvement in motor function, peripheral nerve surgery was deferred. The patient was cleared to begin rehabilitation with changes to pitching mechanics.
Conclusions:
Although considered uncommon, isolated musculocutaneous neuropathy is likely underrecognized in overhead athletes due to its overlap with conditions such as biceps brachii strain, cervical radiculopathy, brachial plexopathy, and other peripheral neuropathies. The musculocutaneous nerve is at risk of compression particularly where it pierces the coracobrachialis muscle, a site exposed to repetitive stress during pitching.
Musculocutaneous neuropathy should be considered in overhead athletes presenting with elbow flexion weakness, biceps atrophy, and/or forearm sensory changes. Recognizing this diagnosis early can help identify indications for surgical intervention, guide rehabilitation, and support a timely return to sports.
