Distal hereditary upper limb muscular atrophy.

OBJECTIVES To identify the clinical, electrophysiological, and genetic characteristics of a family with an unusual form of hereditary motor neuron disease. METHODS Surviving members of a pedigree in which affected members presented with weakness and atrophy of distal musculature in the upper limbs were examined clinically and electrophysiologically, and had genetic testing. RESULTS The disease was autosomal dominantly inherited and manifested as weakness and atrophy of distal musculature in the upper limbs, with minimal involvement of lower limbs, brisk reflexes, minimal sensory findings, and considerable variability in severity among the affected persons. Nerve conduction studies disclosed near normal motor conduction velocity, reduced motor compound action potential amplitude, prolonged distal motor latency, prolonged sensory latency, and normal sensory compound action potential amplitude. Needle electrode examination showed reduced number and increased size of motor unit potentials, but no fibrillations or fasciculations. CONCLUSION Distal upper limb muscular atrophy is a distinct clinical entity.