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. Participates: Twenty FM patients, and two age/sex matched control groups; 20 rheumatoid arthritis patients and 20 healthy controls. Ten micrograms of norepinehrine dilutes in 0.1 mL of saline solution were injected in a forearm. The contrasting substance, 0.1 mL saline solutionalone, was injected in the opposite forearm. Maximum local pain elicted during the 5 minutes post-injection was graded on a visual analog scale (VAS). Norepinephrine-evoked pain was diagnoses 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 ± SD2.5 ± 2.5) when compared to rheumatoid arthritis patients (0.3 ± 0.7), and healthycontrols (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.

BMC Musculoskelet Disord 2002; 3(2)