Serum melatonin level in ankylosing spondylitis: is it increased in active disease?

In the recent years, the role of melatonin (MLT) in the pathogenesis of inflammatory arthritis has been investigated, and the serum levels of MLT have been evaluated, but clinical study concerning MLT and ankylosing spondylitis (AS) is little reported in literature. We aimed to investigate the serum levels of MLT and their relation with the disease activity parameters of patients with AS. Forty AS patients and 40 healthy controls (matched for age and sex with the patients) participated in this study. Demographic and clinical data were collected and assessed. Disease activity of AS patients was assessed clinically according to the Bath AS Disease Activity Index (BASDAI), while AS functional impairment was assessed using the Bath AS Functional Index (BASFI). Serum samples were collected from all subjects to evaluate serum MLT, ESR, and CRP. Serum MLT levels were significantly increased in AS patients as compared to healthy controls (95% CI: 4.63, 8.77, P < 0.001). ESR and CRP are significantly higher in the AS patients compared with the controls (P < 0.001). AS patients with active disease had significantly higher ESR (P = 0.0151), CRP (P = 0.0124), and BASFI (P = 0.0016). Also, the MLT serum level in AS patients with BASDAI ≥40 was 39.7 ± 6.2 pg/ml compared with 35.2 ± 3.5 pg/ml in AS patients with BASDAI <40 (95% CI: 1.22, 7.78, P = 0.0106). Also, serum MLT level was significantly higher in the AS patients with enthesopathy than those without enthesopathy. Serum MLT levels were correlated with the duration of morning stiffness, BASDAI, BASFI, and CRP but not with ESR or duration of the disease. Serum levels of MLT were significantly increased in AS patients as compared to healthy controls. MLT levels correlated positively with BASDAI, BASFI, duration of morning stiffness, and CRP levels. Thus, it seems that MLT levels reflect the disease activity in AS patients.