Genetically confirmed Huntington's disease masquerading as motor neuron disease.

We describe a patient with Huntington's disease (HD) who showed asymmetrical upper limb amyotrophy as a main manifestation. Chorea and psychiatric symptoms were not prominent. Electromyography revealed generalized active and chronic denervation and fasciculations. A genetic test showed 46 CAG repeats in the huntingtin gene. Asymmetrical amyotrophy restricted to the upper limb has been reported in some patients with progressive chorea and amyotrophy without acanthocytosis, but genetically proven cases of HD have rarely been reported. It is not known why only a few HD patients show the motor neuronal loss; however, certain as-yet-unidentified genetic factors combined with some environment factors and the underlying cellular dysfunctions by polyglutamine aggregation could be responsible for the motor neuronal loss similar to that in amyotrophic lateral sclerosis.