Peripheral nerve involvement in spinocerebellar ataxias.

BACKGROUND In autosomal dominant cerebellar ataxias (ADCAs), it is unclear whether the associated peripheral nerve involvement is always a typical length-dependent axonopathy rather than primary neuronopathy due to neuronal degeneration in the spinal anterior horns and/or dorsal root ganglia. OBJECTIVE To study the nature and extent of peripheral nerve involvement in patients with ADCA. PATIENTS AND METHODS Standardized clinical and electrophysiologic studies of 27 genotyped patients with ADCA were conducted prospectively, with special emphasis on the distinction between primary neuronopathy and dying-back axonopathy. RESULTS Electrophysiologic evidence of involvement of the peripheral nervous system was present in 70% of patients. Findings were compatible with dying-back axonopathy in 30%, while in 40% of patients, neuronopathy was diagnosed. Patients with spinocerebellar ataxia (SCA) 1 and SCA2 mostly displayed features of neuronopathy, while patients with SCA3 and SCA7 displayed both neuronopathy and axonopathy. In SCA6, no significant peripheral nerve involvement was demonstrated. We did not observe an influence of age, disease duration, or ataxia severity on the presence or type of peripheral nerve involvement. CONCLUSIONS Peripheral nerve involvement in ADCA manifests not only as distal axonal neuropathy, but also as primary neuronopathy. Electrodiagnostic studies in this group of patients should be conducted in such a way that primary neuronopathy is detected.