1550 - Musculocutaneous Nerve Mononeuropathy Localized with Neuromuscular Ultrasound

Musculocutaneous nerve mononeuropathy secondary to massage therapy with associated ultrasonographic findings

Case Description:

A 39-year-old female presented with 16 days of right arm weakness following a deep tissue massage which targeted the chest, axilla, trapezius, and rhomboid regions. Her symptoms began immediately following the massage. She denied neck or arm pain but endorsed numbness with loss of fine touch and pinprick sensation throughout the right lateral forearm. On examination there was isolated weakness with elbow flexion and supination. MRI of the brachial plexus was unremarkable. Nerve conduction studies revealed an 86% conduction block of the musculocutaneous nerve between the axilla and supraclavicular stimulation sites with needle electromyography demonstrating markedly reduced motor unit recruitment in the biceps brachii and coracobrachialis. Neuromuscular ultrasound (NMUS) revealed asymmetric swelling and loss of the normal fascicular pattern of the musculocutaneous nerve. Management included monitoring for 4 weeks in which patient had near-complete resolution of symptoms. Repeat studies 2 months later showed improving electrophysiologic abnormalities.

Discussions: Isolated musculocutaneous mononeuropathy is a rare condition and is often associated with trauma or iatrogenic surgical injury. Due to its subtle presentation, a high index of suspicion is essential. Electrodiagnostic studies help localize the lesion and confirm nerve involvement. NMUS adds diagnostic value by allowing for direct visualization of nerve abnormalities including focal swelling or asymmetric loss of fascicular pattern.

Conclusions: The combined use of NMUS and electrodiagnostics provides critical, complementary information for accurate diagnosis which may be more easily obtained compared to MRI.