RESUMEN
INTRODUCTION: Cramp-fasciculation syndrome is a peripheral nerve hyperexcitability disorder, which could be caused by inflammatory neuropathy. CASE REPORT: We describe a 51-year-old woman who presented with a 4- to 5-year history of fasciculations and painful cramping of the right thenar eminence. RESULTS: Electrophysiological studies showed motor conduction block in the right median nerve between the axilla and the elbow with fasciculation potentials and cramp discharges on electromyography in the right abductor pollicis brevis muscle. High titers of serum anti-GM1 immunoglobulin M antibodies were detected. CONCLUSIONS: Monofocal motor neuropathy of the right median nerve was diagnosed. Intravenous immunoglobulin treatment led to significant improvement of symptoms and signs. Although fasciculations and cramps have been reported in multifocal motor neuropathy and are considered supporting criteria for the diagnosis, the occurrence of cramp-fasciculation syndrome as the presenting feature and predominant manifestation in monofocal motor neuropathy, a variant of multifocal motor neuropathy, is unique. Muscle Nerve 56: 828-832, 2017.