N140 Latency as a Novel Biomarker for the Evaluation of Somatosensory Dysfunction in Patients with Spinocerebellar Ataxia Type 2.

The N140 component of long-latency somatosensory evoked potentials (LL-SEPs), which is associated with passive attention, may offer a valuable adjunct to short-latency potentials (SL-SEPs) such as N20 in evaluating somatosensory function in spinocerebellar ataxia type 2 (SCA2), yet no previous studies have examined this component in this population. To address this gap, we enrolled 28 patients with SCA2 and 34 age-matched healthy controls, recording LL-SEPs (N140) from the Cz electrode referenced to linked mastoids following second-finger cutaneous stimulation, while N20 potentials were obtained via standard procedures. Clinical assessment in patients included the Scale for the Assessment and Rating of Ataxia (SARA) and CAG repeat length measurement. Compared with controls, SCA2 patients showed significantly prolonged latencies for both N140 and N20 components; however, while mean N20 amplitude was markedly reduced in patients, N140 amplitude did not differ between groups. Notably, both N140 and N20 latencies correlated positively with SARA scores. These findings indicate that the N140 potential is a valuable complement to the N20 for assessing somatosensory dysfunction in SCA2, not only because it is relatively easy to record, but more importantly because it probes higher-order cortical networks involved in cognitive somatosensory processing-networks not captured by N20. The prolonged N140 latency observed here likely reflects the defective thalamo-cortical and cerebello-cortical interactions that underpin SCA2 pathology.