1/24/04


Evidence for spinal cord hypersensitivity in chronic pain after whiplash

injury and in fibromyalgia.



Author(s): Banic B; Petersen-Felix S; Andersen O; Radanov B; Villiger P;

Arendt-Nielsen L; Curatolo M;



Patients with chronic pain after whiplash injury and fibromyalgia patients

display exaggerated pain after sensory stimulation. Because evident tissue

damage is usually lacking, this exaggerated pain perception could be

explained by hyperexcitability of the central nervous system. The

nociceptive withdrawal reflex (a spinal reflex) may be used to study the

excitability state of spinal cord neurons. We tested the hypothesis that

patients with chronic whiplash pain and fibromyalgia display facilitated

withdrawal reflex and therefore spinal cord hypersensitivity. Three groups

were studied: whiplash (n=27), fibromyalgia (n=22) and healthy controls

(n=29). Two types of  transcutaneous electrical stimulation of the sural

nerve were applied: single stimulus and five repeated stimuli at 2 Hz.

Electromyography wasrecorded from the biceps femoris muscle. The main

outcome measurement was the minimum current intensity eliciting a spinal

reflex (reflex threshold). Reflex thresholds were significantly lower in the

whiplash compared with the control group, after both single (P=0.024) and

repeated (P=0.035) stimulation. The same was observed for the fibromyalgia

group, after both stimulation modalities (P=0.001 and 0.046, respectively).

We provide evidence for spinal cord hyperexcitability in patients with

chronic pain after whiplash injury and in fibromyalgia patients. This can

cause exaggerated pain following low intensity nociceptive or innocuous

peripheral stimulation. Spinal hypersensitivity may explain, at least in

part, pain in the absence of detectable tissue damage.



Pain.; 2004 Jan;107(1-2) p7 - 15