Hereditary motor and sensory neuropathy with proximal predominance (HMSN-P).

Hereditary motor and sensory neuropathy with proximal predominance (HMSN-P) is a rare disorder inherited in an autosomal dominant fashion. Patients present with slowly progressive proximal-predominant weakness, painful muscle cramps, fasciculations, large-fiber sensory loss, and areflexia. Electrodiagnostic (EDX) studies typically reveal abnormalities consistent with a sensorimotor neuronopathy. A patient with HMSN-P underwent EDX studies, revealing ongoing and chronic neurogenic denervation, motor unit instability, and neuromyotonic discharges, further defining the spectrum of EDX findings in HMSN-P. The clinical, pathological, and genetic features are also reviewed. The appearance of HMSN-P in the United States and elsewhere calls for clinicians in nonendemic regions to be familiar with this rare disorder, which has typically been geographically confined.