title: Evidence for spinal cord hypersensitivity in chronic pain after whiplash injury and in fibromyalgia.
abstract: 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 was recorded 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.
authors.affiliation: Division of Pain Therapy, Department of Anesthesiology, University Hospital of Bern, Inselspital, 3010 Bern, Switzerland.
authors.forename: Borut
authors.initials: B
authors.lastname: Banic
authors.forename: Steen
authors.initials: S
authors.lastname: Petersen-Felix
authors.forename: Ole K
authors.initials: OK
authors.lastname: Andersen
authors.forename: Bogdan P
authors.initials: BP
authors.lastname: Radanov
authors.forename: P M
authors.initials: PM
authors.lastname: Villiger
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen
authors.forename: Michele
authors.initials: M
authors.lastname: Curatolo
mesh_terms: D000328:Adult; D002908:Chronic Disease; D004576:Electromyography / Q000379:methods; D005260:Female; D005356:Fibromyalgia / Q000150:complications*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology / Q000528:radiation effects; D010146:Pain / Q000209:etiology / Q000503:physiopathology*; D010147:Pain Measurement / Q000379:methods; D017288:Pain Threshold / Q000502:physiology*; D011594:Psychometrics; D012018:Reflex / Q000502:physiology / Q000528:radiation effects; D013116:Spinal Cord / Q000503:physiopathology*; D004561:Transcutaneous Electric Nerve Stimulation / Q000379:methods; D014911:Whiplash Injuries / Q000150:complications*