[Skeletal muscle MRI in a patient with neuralgic amyotrophy]

Neuralgic amyotrophy has been attributed to lesions in the brachial plexus. However, recent studies suggest mononeuropathy multiplex as an underlying pathology at least in a group of patients with neuralgic amyotrophy. We report a man who developed weakness of finger extensors following severe shoulder pain. Neurological examination revealed weakness in the muscles innervated by the left posterior interosseus nerve and the ulnar nerve. We diagnosed him with neuralgic amyotrophy based on the typical clinical course and the neurological and neurophysiological findings. A skeletal muscle MRI revealed abnormal high T2 and STIR signals in the left triceps brachialis muscle, which is innervated by a proximal branch of the radial nerve, and in the muscles innervated by the posterior interosseous and ulnar nerves. The distribution of the denervated muscles suggested that our patient had combined lesions of the peripheral nerve branches rather than the brachial plexopathy. Our report highlights the potential of MRI for detecting denervated muscles in neuralgic amyotrophy.