Varied electrophysiologic patterns in spinocerebellar ataxia type 2

The autosomal dominant ataxias are a heterogenous group of disorders. Almost 30 different genetic loci have been identified. Spinocerebellar ataxia type 2 (SCA2) is one of many autosomal dominant cerebellar ataxias. Electrophysiologic studies in SCA2 have shown mainly a sensory neuropathy or neuronopathy. To determine if electrophysiologic testing reveals concomitant or isolated involvement of motor nerves in SCA2 we reviewed historic and electrophysiologic data on all cases of genetically confirmed SCA2 who underwent nerve conduction studies and needle electromyographic during initial evaluation at our institution. We performed electrophysiologic studies in six genetically confirmed, unrelated, cases of SCA2 and discovered that in three patients, there were findings consistent with motor neuronopathy or neuropathy without sensory involvement. One patient had normal results and only one had a pure sensory neuropathy or neuronopathy. The sixth patients had mixed sensorimotor neuropathy. This is the first study that demonstrates isolated involvement of motor neurons and/or axons occur in SCA2. Therefore, electrophysiologic findings in SCA2 are not limited to mainly a sensory neuropathy but are varied and can even mimic slowly progressive motor neuron disease.