A 47-year-old man presents with a 13-year history of weakness and atrophy of the right hand muscles. Thoracic outlet syndrome surgery did not help. CK level and CSF examination were normal. Cervical MRI was normal. NCS showed no conduction block. The CMAPs of the right median and ulnar nerves were reduced. Sensory responses were normal. EMG revealed diffuse chronic denervation of the right arm muscles.

The lesion is likely located at the level of:
1. Motor neurons
2. Motor nerves
3. Brachial plexus
4. Axons
5. Myelin

Find the answer and diagnosis in the next edition of Practical Neurology or online, posted along with the patient video at PracticalNeurology.com.

Case selected from Dr. Shaibani’s Video Atlas of Neuromuscular Diseases, now available from Oxford University Press. Aziz Shaibani, MD, FACP, FAAN is Director of Nerve & Muscle Center of Texas and Clinical Associate Professor of Medicine at Baylor College of Medicine in Houston, TX. He is also Adjunct Professor of Neurology at Kansas University Medical Center in Kansas City, Kansas.