Correlation analysis between excitability in the somatosensory cortex and structural changes in amyotrophic lateral sclerosis.

Objective: We aimed to investigate the excitability of the somatosensory cortex and its relationship to structural changes in motor and sensory pathways, and motor excitability in amyotrophic lateral sclerosis (ALS). Patients and method: We included all consecutive individuals with ALS, fulfilling the "definite" or "probable" ALS criteria. We recorded surround inhibition (SI) and recovery function (RC) of somatosensory evoked potentials (SEPs), resting motor threshold, and cortical silent period (cSP), and performed volumetric analysis and diffusion tensor imaging (DTI). Results: We included 15 patients with ALS and 12 healthy individuals of similar age and sex. At the group level, the mean SEP-RC% at ISI 5 ms was higher in the ALS group than in healthy participants (all SEP-RC% at 5 ms p < 0.001). SEP-SI was lost in one-third of individuals with ALS. A negative correlation was found between the duration of the cSP and SEP-RC%, whereas no correlations were observed between SEP parameters and radiological volumetric analysis of the corticospinal tract, medial lemniscus, or cortical thickness of the precentral and postcentral gyri. Conclusion: Somatosensory hyperexcitability is present in ALS, and SI is lost in a subset of patients with ALS. Significance: Somatosensory hyperexcitability correlates well with cSP but not with structural changes.