title: Pain inhibition is deficient in chronic widespread pain but normal in major depressive disorder.
abstract: BACKGROUND
  Given the complex relationships between fibromyalgia and major depressive disorder (MDD), it has been suggested that fibromyalgia is a "masked" MDD. In experimental settings, fibromyalgia is associated with lowered pain thresholds (hyperalgesia) and deficient pain inhibition. Similarly, it has been recently proposed that the proneness of patients with MDD to develop chronic pain results from a deficit in pain inhibition. This cross-sectional study measured experimentally induced pain perception and inhibition in patients with MDD and patients with fibromyalgia.
  
  
  METHODS
  Participants were 29 patients with fibromyalgia (American College of Rheumatology criteria), 26 patients with MDD (DSM-IV criteria), and 40 healthy controls who did not differ in age, sex, or the presence or absence of a menstrual cycle. Data were collected between June 2007 and May 2008. Thermal stimuli were used to measure pain thresholds. Pain inhibition was elicited using a tonic thermal test (Peltier thermode) administered before and after activation of the diffuse noxious inhibitory controls (DNIC) by means of a cold pressor test.
  
  
  RESULTS
  Thermal pain thresholds were higher in healthy controls compared to patients with MDD and patients with fibromyalgia. Pain ratings during the cold pressor test were lower in healthy controls and patients with MDD relative to patients with fibromyalgia. Finally, DNIC efficacy was stronger in healthy controls compared to patients with fibromyalgia, while no significant differences were found between healthy controls and patients with MDD.
  
  
  CONCLUSIONS
  Our results suggest that (1) fibromyalgia and MDD are both associated with signs of hyperalgesia, (2) hyperalgesia is more pronounced in fibromyalgia, and (3) the deficit of pain inhibition is specific to fibromyalgia. As such, these results suggest that there is an overlap between fibromyalgia and MDD, but that fibromyalgia can be distinguished from MDD in terms of DNIC efficacy.
authors.affiliation: Département de Neurochirurgie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Edith
authors.initials: E
authors.lastname: Normand
authors.forename: Stéphane
authors.initials: S
authors.lastname: Potvin
authors.forename: Isabelle
authors.initials: I
authors.lastname: Gaumond
authors.forename: Guylaine
authors.initials: G
authors.lastname: Cloutier
authors.forename: Jean-François
authors.initials: JF
authors.lastname: Corbin
authors.forename: Serge
authors.initials: S
authors.lastname: Marchand
mesh_terms: D000328:Adult; D003430:Cross-Sectional Studies; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000503:physiopathology / Q000523:psychology*; D005260:Female; D005356:Fibromyalgia / Q000175:diagnosis / Q000503:physiopathology / Q000523:psychology*; D006801:Humans; D006930:Hyperalgesia / Q000175:diagnosis / Q000503:physiopathology / Q000523:psychology*; D008297:Male; D008875:Middle Aged; D009433:Neural Inhibition / Q000502:physiology*; D009619:Nociceptors / Q000502:physiology; D010146:Pain / Q000503:physiopathology / Q000523:psychology*; D010147:Pain Measurement / Q000706:statistics & numerical data; D017288:Pain Threshold / Q000502:physiology*; D011594:Psychometrics; D012016:Reference Values