Background: Fibromyalgia syndrome (FMS) is a disease of unknown pathogenesis characterized by chronic musculoskeletal pain. FMS has been also associated with altered endocrinological responses, but findings are inconsistent.
Purpose: The aim of the present study was to investigate free salivary cortisol levels in FMS patients compared with healthy controls with a particular focus on the cortisol awakening response (CAR). The saliva samples were collected in a controlled hospital-hotel setting, in which the participants' compliance was high and a number of potential confounders were analyzed.
Method: Twenty-nine chronic female FMS patients and 29 age-matched healthy female controls were recruited. Salivary cortisol samples were investigated eight times: in the afternoon when participants arrived at the hospital, after stress provocation (to be reported separately), in the evening, before they went to sleep, upon awakening, 30 and 60 min later, and during the afternoon of the second day. Questionnaires measuring pain levels, sleeping problems, perceived stress, and personality were administered to the participants. Other psychophysiological measurements were used to assess sleep quality and heart rate.
Results: Patients with FMS had significantly lower cortisol levels during the day, most pronounced in the morning (CAR). The potential confounders analyzed did not influence the results. As expected, FMS patients reported more pain, stress, sleeping problems, anxiety, and depression.
Conclusion: The results lend support to the hypothesis of a dysfunction in the hypothalamus-pituitary-adrenal axis in FMS patients, with generally lower cortisol values, most pronounced upon awakening (CAR).