Research article

Norepinephrine-evoked pain in fibromyalgia. A randomized pilot study [ISRCTN70707830]

Manuel Martinez-Lavin , Marcela Vidal , Rosa-Elda Barbosa , Carlos Pineda , Jose-Miguel Casanova and Arnulfo Nava

Rheumatology Department Instituto Nacional de Cardiología Ignacio Chávez. Juan Badiano 1, 14080 Mexico D.F. México

author email corresponding author email

BMC Musculoskeletal Disorders 2002, 3:2doi:10.1186/1471-2474-3-2

Published:	16 January 2002

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. Participants: 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.