Isolated Musculocutaneous Neuropathy Secondary to an Immune-Mediated Brachial Plexopathy: A Case Report of a Rare Phenotype With a Side Note on Patterns of Weakness and an Update on Nerve Pathology

We describe a 50-year-old man who developed a low-frequency pattern of weakness, musculocutaneous neuropathy, with weakness of the biceps, coracobrachialis and brachialis in an immune-mediated brachial plexopathy. The aim of this article is to highlight both the low- and high-frequency patterns of weakness of the immune-mediated brachial plexopathies, and we focus on the patterns of recognition. We then segue into the pathology of the immune-mediated plexopathies and highlight the recent spectacular magnetic resonance imaging studies that demonstrate hourglass constrictions of peripheral nerves outside of the brachial plexus in afflicted patients. This opens up a window for the exciting possibility of neurolysis of constricted nerves in patients who have not responded adequately to immunotherapy.