Abnormalities of the Descending Inhibitory Nociceptive Pathway in Functional Motor Disorders

Abstract

BackgroundPain is a common disabling non‐motor symptom affecting patients with functional motor disorders (FMD).ObjectiveWe aimed to explore ascending and descending nociceptive pathways with laser evoked potentials (LEPs) in FMD.MethodsWe studied a “bottom‐up and top‐down” noxious paradigm applying a conditioned pain modulation (CPM) protocol and recorded N2/P2 amplitude in 21 FMD and 20 controls following stimulation of both right arm and leg at baseline (BS) (bottom‐up), during heterotopic noxious conditioning stimulation (HNCS) with ice test (top‐down) and post‐HNCS.ResultsWe found a normal ascending pathway, but reduced CPM response (lower reduction of the N2/P2 amplitude) in FMD patients, by stimulating both upper and lower limbs. The N2/P2 amplitude ratio*100 (between the HNCS and BS) was significantly higher in patients with FMD than HC.ConclusionsOur results suggest that pain in FMD possibly reflects a descending pain inhibitory control impairment, therefore, providing a novel venue to explore the pathophysiology of pain in FMD. © 2024 International Parkinson and Movement Disorder Society.