Serotonin concentration in serum of patients with generalized tendomyopathy (fibromyalgia) and chronic polyarthritis

: The serum concentration of serotonin (S-5-HT) was measured in 31 patients with primary fibromyalgia, 21 patients with rheumatoid arthritis (RA) (15 of them with secondary fibromyalgia) and 20 healthy volunteers. Both patients with primary fibromyalgia and rheumatoid arthritis had significantly lower S-5-HT levels when compared to healthy controls, and S-5-HT concentrations in patients with secondary fibromyalgia were even significantly lower than those of RA-patients. Unlike the patients with rheumatoid arthritis, a significant correlation between S-5-HT level and the number of "tender points" as well as mean pressure tenderness at 24 different points was found in patients with primary fibromyalgia. Conversely, in patients with rheumatoid arthritis the S-5-HT level correlated significantly with erythrocyte sedimentation rate. These results suggest different pathological mechanisms of S-5-HT decrease in patients with primary fibromyalgia and rheumatoid arthritis. On the other hand, they raise the question whether secondary fibromyalgia may be a pathogenetically different syndrome mimicking symptomatically primary fibromyalgia.