(Kiosk 1) New-onset Rapid Functional Decline in Dominant Arm Decades After Obstetric Brachial Plexus Injury: A Case Report

Case Diagnosis: Patient with obstetric brachial plexus injury (OBPI) with rapidly developed new onset median mononeuropathy at the wrist and ulnar mononeuropathy at the elbow.

Case Description or Program Description: 60 year old male with a history of a right-sided OPBI presents for electrodiagnostic evaluation of the right arm. He has longstanding proximal weakness in this arm but has been very functional. Over the past year working at home typing, he has noticed reduced function in the right hand. Exam demonstrates hand intrinsic weakness, decreased sensation in all right-hand digits, negative provocative testing.

Setting: Outpatient PM+R

Assessment/Results: NCS demonstrated absent ulnar SNAP, decreased ulnar CMAP and slowing at the elbow. Additionally, there was slowing of the median nerve at the wrist. Electromyography demonstrated reduced recruitment of large amplitude, long duration motor units throughout the right arm. There was increased spontaneous/insertional activity and polyphasia only in the ulnar innervated muscles. During the subsequent carpal tunnel release and ulnar decompression, operative notes indicated intact median nerve but severe contracture and scarring around the medial epicondyle.

Discussion (relevance): Could his OBPI be a predisposing factor for the development of subsequent mononeuropathies, even decades later? Increased innervation ratio (number of muscle fibers per motor unit) following nerve recovery would theoretically imply that subsequent minor axonal damage would result in more severe denervation and predisposition for mono-neuropathies. There is a paucity of literature on this question. Further studies will be helpful to investigate this question.
Altered movement patterns and sensory deficits following OBPI may also predispose to compressive mononeuropathies. Counseling on behavioral modifications and biomechanics may reduce the risk for compressive mononeuropathies in these patients.

Conclusions: Prior brachial plexus injury may predispose to future mono-neuropathies. Specific further research is suggested, and patient counseling may be recommended.