Altered neurocognitive processing of tactile stimuli in patients with Complex Regional Pain Syndrome (CRPS)

Abstract

Chronic pain in CRPS has been linked to tactile misperceptions and deficits in somatotopic representation of the affected limb. Here, we identify altered cognitive processing of tactile stimuli in CRPS patients that we propose marks heterogeneity in tactile decision-making mechanisms. In a case-control design, we compared middle and late-latency somatosensory-evoked potentials (SEPs) in response to pseudo-randomised mechanical stimulation of the digits of both hands (including CRPS-affected and non-affected sides) between 13 CRPS patients and 13 matched healthy controls. During a task to discriminate the digit simulated, patients (compared to controls) had significantly lower accuracy and slowed response times but with high between-subject variability. At middle latencies (124-132ms), tactile processing in patients relative to controls showed decrements in superior parietal lobe and precuneus (that were independent of task demands) but enhanced activity in superior frontal lobe (that were task-dependent). At late latencies, patients showed an augmented P300-like response under task demands that localised to supplementary motor area (SMA). Source activity in SMA correlated with slowed response times, while its scalp representation intriguingly correlated with better functioning of the affected limb, suggesting a compensatory mechanism. We present evidence of altered but highly variable cognitive processing (124 -268ms latency) in response to mechanical tactile stimuli in patients with CRPS compared to healthy controls. Such mid-to-late latency responses could potentially provide convenient and robust biomarkers of abnormal perceptual decisionmaking mechanisms in CRPS to aid in clinical detection and treatment. Future research should investigate the clinical utility of these putative markers of tactile decision-making mechanisms in CRPS.

A Novel Finger Illusion Reveals Reduced Weighting of Bimanual Hand Cortical Representations in People With Complex Regional Pain Syndrome

“…Complex regional pain syndrome (CRPS) is characterised by excessive pain, usually in a peripheral limb such as the hand, and affects sensation, movement and function 32 . Quantified deficits include higher thresholds for two-point discrimination in the index finger 45 , impaired hand size estimation 35,44 , finger misidentification 14,33 , tactile processing disturbances 28 ; errors in bilateral limb positioning 30 , fine motor 26 and motor imagery performance 34,49,50 . These deficits implicate distortions in body representation 53 and are corroborated by evidence of cortical re-organisation in CRPS 9,10 , although much remains unclear 29 .…”