Pattern of Peripheral Nerve Involvement in Spinocerebellar Ataxia Type 2: a Neurophysiological Assessment

Peripheral neuropathy is frequent in spinocerebellar ataxia type 2 (SCA2), but the pattern and characteristics of nerve involvement are still an unsettled issue. This study aimed to evaluate the prevalence, extent, and distribution of nerve involvement in SCA2 patients through neurophysiological studies. Thirty-one SCA2 patients and 20 control subjects were enrolled in this study. All subjects were prospectively evaluated through electromyography, including nerve conduction, needle electromyography in proximal and distal muscles of the upper and lower limbs, and sural radial amplitude ratio (SRAR). We aimed to differentiate distal axonopathy from diffuse nerve commitment, characterizing neuronopathy. Nerve involvement was observed in 83.6 % (26 individuals) of SCA2 patients. Among these, 19 had diffuse sensory abnormalities on nerve conduction predominantly on the upper limbs, with diffuse chronic denervation on needle electromyography and elevated SRAR values. Four individuals had only diffuse sensory involvement, and 2 had only motor involvement on needle evaluation and normal nerve conduction. These were interpreted as neuronopathy due to the diffuse distribution of the involvement. One individual had distal sensory axonopathy, with lower limb predominance. In this study, we found neuronopathy as the main pattern of nerve involvement in SCA2 patients and that motor involvement is a frequent feature. This information brings new insights into the understanding of the pathophysiology of nerve involvement in SCA2 and sets some key points about the phenotype, which is relevant to guide the genetic/molecular diagnosis.