Plasma oxytocin levels in female fibromyalgia syndrome patients

Fibromyalgia syndrome (FMS) is a chronic pain disorder, where 90% of the patients struck by the disorder are women. The neuropeptide oxytocin is known to have antinociceptive and analgesic, as well as anxiolytic and antidepressant effects, which makes this neuropeptide of interest in fibromyalgia research. The aim of this study was to assess oxytocin concentrations in female FMS patients with different hormonal status and in depressed and non-depressed patients and relate oxytocin concentrations to adverse symptoms as pain, stress, depression, anxiety and to the positive item happiness.

Thirty-nine patients and 30 controls registered these symptoms daily during 28 days and blood samples for the assessment of oxytocin were drawn twice in all patients and controls. Besides the daily ratings, depression was also estimated with the self-rating instrument Beck Depression Inventory (BDI).

Depressed patients according to the BDI differed significantly with low levels of oxytocin compared to the non-depressed patients and the controls. Low levels of oxytocin were also seen in high scoring pain, stress and depression patients according to the daily ratings; however, these subgroups were small. A negative correlation was found between the scored symptoms depression and anxiety and oxytocin concentration, and a positive correlation between the item happiness and oxytocin. The oxytocin concentration did not differ between the hormonally different subgroups of patients or controls.

The results suggest that the neuropeptide oxytocin may, together with other neuropeptides and neurotransmitters, play a role in the integration of the stress axes, monoaminergic systems and the pain processing peptides in the pathophysiologic mechanisms responsible for the symptoms in the FMS.