Correlation between nocturnal heart rate variability parameters and circulating neuropeptides in patients suffering from fibromyalgia.

Objectives: A consistent line of investigation proposes fibromyalgia (FM) as a stress-evoked, sympathetically maintained neuropathic pain syndrome. The purpose of this study was to measure dysautonomia-associated neuropeptide serum levels in women suffering from FM and to correlate these levels with heart rate variability parameters and disease severity.

Methods: We studied 23 women suffering from FM without comorbid conditions and 15 age and body mass index-matched healthy women. At the time of the study, all participants were free from medications that could affect the autonomic nervous system. Time-domain parameters were extracted from nocturnal (00.00 to 06.00 hours) heart rate variability Holter recordings. The following 7 neuropeptide levels were measured via the 7-Plex Human Neuropeptide Magnetic Kit Milliplex MAP: alpha-melanocyte-stimulating hormone, beta-endorphin, cortisol, neurotensin, orexin, oxytocin and substance P.

Results: The serum levels of beta-endorphin (669.24±186.28 vs. 541.71±146.26 pg/ml, p=0.028) and neurotensin (156.23±58.15 vs. 116.64±47.93 pg/ml, p=0.016) were significantly greater in patients with FM. Both neuropeptides were negatively correlated with the nocturnal heart rate R-R interval standard deviation (Rho=-0.52 p=0.025 and Rho=-0.6, p=0.003) and with the FIQR "tenderness to touch" (Rho -0.49 and Rho -0.41, p<0.05).

Conclusions: The serum levels of beta-endorphin and neurotensin in women suffering from FM correlate with nocturnal heart rate variability parameters, revealing sympathetic hyperactivity. The unexpectedly increased circulating levels of these two analgesic neuropeptides in the FM group can be interpreted as a homeostatic attempt by the central nervous system to ease peripherally generated pain.