Utility of neuromuscular ultrasound and comparison of NMUS with electrodiagnostic tests in dominant spinocerebellar ataxia

Objective: To estimate and compare the prevalence of sensory neuronopathy and neuropathy in autosomal dominant spinocerebellar ataxia (SCA) using neuromuscular ultrasound (NMUS) and traditional electrodiagnostic tests (EDX). Methods: We compared NMUS [median and ulnar nerve cross-sectional areas (CSAs)] with EDX [sensory (sural, radial, median, ulnar); motor (median, ulnar, tibial)] findings from previously published and newly recruited patients with SCA (44 in total; SCA1 = 8, SCA2 = 27, SCA3 = 2; SCA6 = 7). Sensory neuronopathy was diagnosed by reduced nerve CSA on NMUS and non length-dependent sensory axonal pattern on EDX, and neuropathy by enlarged nerve CSA on NMUS and length-dependent axonal pattern on EDX. Results: Abnormalities were detected significantly more frequently on NMUS than EDX (75 % vs 51 %, p < 0.001), especially sensory neuronopathy (57 % vs 32 %; p < 0.001). Ten of 24 sensory neuronopathies detected by NMUS were missed by EDX. No sensory neuronopathy detected by EDX was missed by NMUS. Conclusions and significance: The prevalence of abnormality, especially sensory neuronopathy, detected in our SCA cohort was significantly higher with NMUS than EDX. This has significant implication for clinical practice. Where NMUS resources are available, NMUS can be proposed as the method of choice for the investigation of sensory neuronopathy in SCA.