title: Norepinephrine-evoked pain in fibromyalgia. A randomized pilot study [ISRCTN70707830].
abstract: BACKGROUND
  Fibromyalgia syndrome displays sympathetically maintained pain features such as frequent post-traumatic onset and stimuli-independent pain accompanied by allodynia and paresthesias. Heart rate variability studies showed that fibromyalgia patients have changes consistent with ongoing sympathetic hyperactivity. Norepinephrine-evoked pain test is used to assess sympathetically maintained pain syndromes. Our objective was to define if fibromyalgia patients have norepinephrine-evoked pain.
  
  
  METHODS
  Prospective double blind controlled study.
  
  
  METHODS
  Twenty FM patients, and two age/sex matched control groups; 20 rheumatoid arthritis patients and 20 healthy controls. Ten micrograms of norepinephrine diluted in 0.1 ml of saline solution were injected in a forearm. The contrasting substance, 0.1 ml of saline solution alone, was injected in the opposite forearm. Maximum local pain elicited during the 5 minutes post-injection was graded on a visual analog scale (VAS). Norepinephrine-evoked pain was diagnosed when norepinephrine injection induced greater pain than placebo injection. Intensity of norepinephrine-evoked pain was calculated as the difference between norepinephrine minus placebo-induced VAS scores.
  
  
  RESULTS
  Norepinephrine-evoked pain was seen in 80 % of FM patients (95% confidence intervals 56.3 - 94.3%), in 30 % of rheumatoid arthritis patients and in 30 % of healthy controls (95% confidence intervals 11.9 - 54.3) (p < 0.05). Intensity of norepinephrine-evoked pain was greater in FM patients (mean +/- SD 2.5 +/- 2.5) when compared to rheumatoid arthritis patients (0.3 +/- 0.7), and healthy controls (0.3 +/- 0.8) p < 0.0001.
  
  
  CONCLUSIONS
  Fibromyalgia patients have norepinephrine-evoked pain. This finding supports the hypothesis that fibromyalgia may be a sympathetically maintained pain syndrome.
authors.affiliation: Rheumatology Department Instituto Nacional de Cardiología Ignacio Chávez, Juan Badiano 1, 14080 Mexico D.F. México. mmlavin@infosel.net.mx
authors.forename: Manuel
authors.initials: M
authors.lastname: Martinez-Lavin
authors.forename: Marcela
authors.initials: M
authors.lastname: Vidal
authors.forename: Rosa-Elda
authors.initials: RE
authors.lastname: Barbosa
authors.forename: Carlos
authors.initials: C
authors.lastname: Pineda
authors.forename: Jose-Miguel
authors.initials: JM
authors.lastname: Casanova
authors.forename: Arnulfo
authors.initials: A
authors.lastname: Nava