The involvement of melatonin in the clinical status of patients with fibromyalgia syndrome.

Objectives: The aim of this study was to evaluate the levels of 6-sulphatoxymelatonin (6-SMT) in the urine of patients with fibromyalgia (FM) and correlate them with the score obtained by these patients in four clinical assessment instruments.

Methods: Fifty-eight women with primary FM and 39 healthy women matched for age and body mass index were included in the study sample. The levels of 6-SMT were evaluated in urine collected from 8 pm until 8 am the next day by the immunosorbent assay. For the clinical evaluation we used the Fibromyalgia Impact Questionnaire (FIQ); Pittsburg Sleep Quality Index (PSQI); Medical Outcomes Study 36-item Short-Form Health Survey (SF-36) and Satisfaction with Life Scale (SWLS). Data normality was assessed using the Kolmogorov-Smirnov test, the differences between groups by means of the Mann-Whitney test and correlation analysis by Spearman's correlation test.

Results: The levels of 6-SMT in the urine of patients with FM were significantly lower than those found in the urine of healthy controls. The score obtained by patients with FM was significantly different from the score achieved by the healthy controls in the four assessment tools. However, no significant correlation between urinary levels of 6-SMT and scores on assessment instruments was observed.

Conclusions: The results of this study do not discard the involvement of melatonin in the pathophysiology of FM, but may suggest that changes in melatonin levels when associated with other neuroimmunoendocrine changes may impact directly and negatively on the manifestation of symptoms that make up the clinical picture of FM.