Background: Chronic musculoskeletal pain may be associated with changes in the balance of algogenic and anti-nociceptive compounds, and that such changes may be visible in plasma samples. We have undertaken an exploratory study to measure the levels of endocannabinoids, related N-acylethanolamines and oxylipins (primarily those derived from linoleic acid) in plasma samples from women with chronic neck pain (NP) and chronic widespread pain (CWP), and to investigate whether the observed levels are associated with the pain experienced by these women.

Methods: Blood samples from 35 women with NP, 15 with CWP and 27 age-matched controls were analysed for the lipids using an ultra performance liquid chromatography coupled to tandem mass spectrometry method. Current pain ("NRSday") and the average pain during the last week ("NRSweek") were rated by the participants using a numerical rating scale.

Results: There were no significant differences in the plasma concentrations of the fifteen lipids investigated between the pain subjects and the controls. However, significant correlations were seen for the NP group between the NRSday scores and the plasma concentrations of the linoleic acid derivatives 9- and 13- hydroxy-10E,12Zoctadecadienoic acid (Spearman's rho values 0.51 [P=0.0016]) and 0.53 [P=0.0011], respectively).

Conclusions: The data obtained in this exploratory study are consistent with a model whereby the underlying inflammatory nature of the musculoskeletal disorders leads both to an increase in the NRSday scores and the hydroxy-10E,12Z-octadecadienoic acid levels, and these increases further influence the perceived pain of in the NP subjects.