Background Several reports suggest that, in most cases, fibromyalgia syndrome (FS) begins as a localised pain syndrome which may precede for months or years the development of the full-blown disease. Thus, some patients who currently present with chronic low back pain (LBP) may in future develop FS.
Objectives To study FS signs and symptoms and serum serotonin (5-hydroxytryptamine, 5-HT) in patients with chronic low back pain syndrome (LBP) in order to identify possible predictors of FS development.
Methods Comparative and correlation analysis of clinical data (pain intensity, tender point count, average pain threshold, functional symptoms, levels of depression and anxiety, feeling of well-being, measures of sleep disturbance) and serum 5-HT in patients with FS (n = 34) and LBP (n = 46).
Results FS patients had higher intensity of pain, higher tender point count, lower average pain threshold, more functional symptoms, higher scores on depression and anxiety scales, decreased feeling of well-being, and more sleep troubles than those with LBP (p < 0.0001 for all comparisons). In both groups, there was a strong interrelationship between functional symptoms, depression, anxiety, feeling of well-being, and the sleep disturbance. Serum 5-HT was lower in FS group when compared to healthy sex- and age-matched controls (n = 26, p < 0.03). Although low serum 5-HT was found in some patients with LBP, the median serum level of the monoamine did not differ significantly from that found in FS and controls. There was no relationship between serum 5-HT and the clinical characteristics in the LBP group. Women with LBP had higher count of tender points (p < 0.0001), lower pain threshold (p < 0.0001), higher median level of depression (p < 0.005), and more disturbed sleep (p < 0.05) than men.
Conclusion As expected, striking differences in clinical characteristics were found between FS and LBP with greater disturbance seen with the FS group. Our study confirms earlier reports suggesting lowered serum 5-HT in FS and provide no support to the hypothesis that there may be a general 5-HT deficiency in LBP. Higher tender point count, decreased pain threshold, depression, and sleep disturbance are possible predictors of FS development in LBP and should be investigated in further prospective research.
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