(Kiosk 4) Multifocal Motor Neuropathy in a 24-year-old Female Presenting with Biceps Atrophy and Weakness: A Case Report

Case Diagnosis: A 24-year-old female with Multifocal Motor Neuropathy (MMN) of the musculocutaneous and long thoracic nerves.

Case Description or Program Description: The patient presented with a six-month history of progressively worsening right biceps atrophy and weakness of right elbow flexion. Further physical exam findings, including decreased strength in right elbow flexion and supination, and absent right biceps deep tendon reflex (DTR), indicated suspicion of musculocutaneous nerve neuropathy and prompted further investigation via Nerve Conduction Study (NCS) and Electromyography (EMG). While EMG demonstrated polyphasic potentials in the right biceps brachii and right brachialis muscles, NCS displayed normal sensory nerve testing components, including the right lateral antebrachial cutaneous nerve. MRI studies of the cervical spine, right shoulder, and biceps were non-contributory. One week clinic follow-up revealed winging of the right scapula. Antibody labs were ordered and the results were positive for antinuclear antibody (ANA) antibodies and negative for anti-ganglioside monosialic acid (GM1).

Setting: Outpatient PM&R clinic.

Assessment/Results: Given the constellation of clinical and EMG/NCS findings, the patient was diagnosed with MMN of the musculocutaneous and long thoracic nerves, due to involvement of the biceps brachii, brachialis, and serratus anterior muscles. Following physical therapy, she reported subjective improvement of weakness 6 weeks post-initial visit. The patient was also recommended to begin intravenous immune globulin (IVIG) treatment.

Discussion (relevance): This report illustrates the complexities in distinguishing MMN from similar neuromuscular pathologies such as chronic inflammatory demyelinating polyradiculoneuropathy (CIDP), amyotrophic lateral sclerosis (ALS), and Parsonage-Turner Syndrome. Through this case, we aim to provide physicians with a reference for the diagnosis of MMN and indications for further evaluation of patients presenting with isolated motor impairment.

Conclusions: Clinical findings of isolated motor weakness without pain or sensory involvement, absent DTRs, and the nature of symptom progression led us to suspect Multifocal Motor Neuropathy over other neuromuscular pathologies.