Focal amyotrophy in multiple sclerosis

Introduction: The assumption that multiple sclerosis (MS) is purely a white matter disease has been challenged in recent years by observations of axonal damage and neuronal loss in gray matter of the cortex, subcortex, and spinal cord. Methods: We report the case of a 71-year-old man with primary progressive MS and longstanding right arm weakness who presented with intermittent right arm pain. Results: Neurological examination showed atrophy, weakness, and hyporeflexia, and electromyography (EMG) showed acute and chronic partial denervation in multiple segments of the right arm. Magnetic resonance imaging (MRI) demonstrated asymmetric volume loss and increased T2 signal in the right anterior spinal cord from C3 to C7, with no evidence of nerve root compression. Conclusions: Lower motor neuron involvement of his right arm was caused by MS with involvement of either the anterior horn cells or the intraspinal motor nerve roots.