78. Cutaneous silent period recordings in demyelinating and axonal polyneuropathies

Abstract

Cutaneous silent period (CSP) is a pause in voluntary muscle contraction following painful cutaneous nerve stimulation which allows to study small-myelinated fibres. We investigated CSP in patients with demyelinating and axonal polyneuropathy (PNP) and explored correlation between CSP changes and neuropathic pain. Eighty demyelinating PNP patients, 178 axonal PNP patients and 265 controls underwent clinical (neurological examination, DN4-Questionnaire) and electrophysiological (motor root conduction time, compound muscle action potentials, sensory nerve action potentials and CSPs of the ulnar nerve) investigations. In the demyelinating PNP group, all electrophysiological latencies were longer with respect to the axonal PNP group and the controls ( p = 0.0001); axonal PNP group had shorter CSP duration with respect to the controls ( p = 0.0001). Axonal PNP patients suffered from painful sensations more than the demyelinating PNP patients ( p = 0.02) but CSP parameters were not different among painful and painless patients. Our findings confirm in a large number of patients that CSP evaluation is effective to study small-fibres dysfunction in both axonal and demyelinating PNP. The lack of correlation between shortened CSP duration and presence of neuropathic pain could suggest that neuropathic pain primarily arises, rather than from altered peripheral signals, from changes in spinal cord plasticity.