O-3-21. Electrophysiological evaluation of peripheral neuropathy in hereditary spinocerebellar ataxia

Peripheral neuropathy often occurs in hereditary spinocerebellar ataxia (hSCA), but the features of nerve involvement have not been fully investigated. We evaluated the prevalence of peripheral neuropathy in hSCAs and classified the underlying pathologies into length-dependent axonopathy and neuronopathy based on sural/radial amplitude ratio (SRAR). SRAR has been reported as a sensitive indicator to differentiate the pathology of peripheral neuropathy. In this study, we defined SRAR less than 0.3 as length-dependent axonopathy, and SRAR more than 0.3 as neuronopathy. We evaluated 22 patients with hSCA (2 patients with SCA1, 1 with SCA2, 12 with SCA3, 2 with SCA6, and 5 with unknown genotypes) and 9 patients with sporadic SCA. Peripheral neuropathy was observed in 13 patients with hSCA (1 SCA1, 1 SCA2, 10 SCA3 and 1 with unknown genotypes). Ten of 13 patients (77%) showed less than SRAR 0.3, which coincided with length-dependent axonopathy. Furthermore, during follow-up for 3 years, three of 5 patients turned into the feature of length-dependent axonopathy from that of neuronopathy. These results indicate that the sural SNAPs might decrease earlier than the radial SNAPs in hSCAs. In conclusion, the length-dependent axonopathy is the dominant form of peripheral neuropathy in patients with hSCA.