title: Does acetaminophen activate endogenous pain inhibition in chronic fatigue syndrome/fibromyalgia and rheumatoid arthritis? A double-blind randomized controlled cross-over trial.
abstract: BACKGROUND
  Although enhanced temporal summation (TS) and conditioned pain modulation (CPM), as characteristic for central sensitization, has been proved to be impaired in different chronic pain populations, the exact nature is still unknown.
  
  
  OBJECTIVE
  We examined differences in TS and CPM in 2 chronic pain populations, patients with both chronic fatigue syndrome (CFS) and comorbid fibromyalgia (FM) and patients with rheumatoid arthritis (RA), and in sedentary, healthy controls, and evaluated whether activation of serotonergic descending pathways by acetaminophen improves central pain processing.
  
  
  METHODS
  Double-blind randomized controlled trial with cross-over design.
  
  
  METHODS
  Fifty-three women (19 CFS/FM patients, 16 RA patients, and 18 healthy women) were randomly allocated to the experimental group (1 g acetaminophen) or the placebo group (1 g dextrose). Participants underwent an assessment of endogenous pain inhibition, consisting of an evaluation of temporal summation with and without conditioned pain modulation (CPM). Seven days later groups were crossed-over. Patients and assessors were blinded for the allocation.
  
  
  RESULTS
  After intake of acetaminophen, pain thresholds increased slightly in CFS/FM patients, and decreased in the RA and the control group. Temporal summation was reduced in the 3 groups and CPM at the shoulder was better overall, however only statistically significant for the RA group. Healthy controls showed improved CPM for both finger and shoulder after acetaminophen, although not significant.
  
  
  CONCLUSIONS
  The influence of acetaminophen on pain processing is inconsistent, especially in the patient groups examined.
  
  
  CONCLUSIONS
  This is the first study comparing the influence of acetaminophen on central pain processing in healthy controls and patients with CFS/FM and RA. It seems that CFS/FM patients present more central pain processing abnormalities than RA patients, and that acetaminophen may have a limited positive effect on central pain inhibition, but other contributors have to be identified and evaluated.
authors.affiliation: Department of Human Physiology and Rehabilitation Sciences, Vrije Universiteit Brussels, Belgium. Mira.Meeus@artesis.be
authors.forename: Mira
authors.initials: M
authors.lastname: Meeus
authors.forename: Kelly
authors.initials: K
authors.lastname: Ickmans
authors.forename: Filip
authors.initials: F
authors.lastname: Struyf
authors.forename: Linda
authors.initials: L
authors.lastname: Hermans
authors.forename: Kevin
authors.initials: K
authors.lastname: Van Noesel
authors.forename: Jorinde
authors.initials: J
authors.lastname: Oderkerk
authors.forename: Luc S
authors.initials: LS
authors.lastname: Declerck
authors.forename: Greta
authors.initials: G
authors.lastname: Moorkens
authors.forename: Guy
authors.initials: G
authors.lastname: Hans
authors.forename: Sofie
authors.initials: S
authors.lastname: Grosemans
authors.forename: Jo
authors.initials: J
authors.lastname: Nijs
mesh_terms: D000082:Acetaminophen / Q000627:therapeutic use*; D000328:Adult; D000368:Aged; D018712:Analgesics, Non-Narcotic / Q000627:therapeutic use*; D001172:Arthritis, Rheumatoid / Q000188:drug therapy* / Q000503:physiopathology; D059333:Central Nervous System Sensitization / Q000187:drug effects; D018592:Cross-Over Studies; D004311:Double-Blind Method; D015673:Fatigue Syndrome, Chronic / Q000188:drug therapy* / Q000503:physiopathology; D005260:Female; D006801:Humans; D008875:Middle Aged; D010146:Pain / Q000188:drug therapy; D017288:Pain Threshold / Q000187:drug effects*; D055815:Young Adult
chemical_list: D018712:Analgesics, Non-Narcotic; D000082:Acetaminophen