Revisiting somatosensory evoked potentials in motor neuron diseases: neurophysiological insights from a large cohort.
OBJECTIVE: To systematically investigate Somatosensory Evoked Potential (SEP) abnormalities in a large cohort of patients with Motor Neuron Disease (MND), and to explore their relationship with Motor Evoked Potentials (MEPs) and clinical phenotypes. METHODS: We retrospectively analyzed 267 patients with confirmed MND who underwent standardized SEPs and transcranial magnetic stimulation. Patients were divided into pure/predominant Upper Motor Neuron (UMN) and pure/predominant Lower Motor Neuron/Amyotrophic Lateral Sclerosis (LMN/ALS) groups. SEP abnormalities were assessed using internal normative data, including prolonged latencies, reduced amplitudes, and increased N20-P25 amplitudes. MEPs were classified semi-quantitatively as normal or abnormal by independent raters. RESULTS: At least one SEP abnormality was detected in 75 % of patients, with no significant differences between the UMN and LMN/ALS groups. Increased N20-P25 amplitudes were observed in both phenotypes, suggesting widespread sensory cortical hyperexcitability across the MND spectrum. In contrast, abnormal MEPs were significantly more frequent in UMN patients (p < 0.001). No significant association was found between SEP abnormalities and MEP findings. Upper- and lower-limb SEP latencies were strongly correlated (all p < 0.001), whereas increased SEP amplitudes did not correlate with latency abnormalities. CONCLUSIONS: SEP abnormalities are highly prevalent in MND and appear largely independent from corticospinal dysfunction. Increased SEP amplitudes likely reflect primary cortical sensory hyperexcitability rather than impaired sensory conduction. SIGNIFICANCE: These findings support the concept of MND as a multisystem network disorder that involves sensory cortical circuits and highlight the role of SEPs in the diagnostic workup.