High melatonin levels are related to spinal ossification in patients with ankylosing spondylitis.

To investigate associations of serum melatonin with spinal ossification and cytokines in ankylosing spondylitis (AS). Serum was obtained from 52 AS patients and 25 healthy controls. Melatonin was measured by ELISA kit; bone morphogenetic protein (BMP)-2, dickkopf-related protein (Dkk)-1, IL-1β, IL-6, IL-17 and TNF-α concentrations were assayed using Luminex multiplex bead system. Osteocalcin and β isomer of C-terminal telopeptide of type I collagen (β-CTX) were measured using electrochemiluminescence immunoassay. Spinal damages were assessed using the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) on radiographs. Serum melatonin was significantly increased in AS patients. Serum melatonin correlated positively with mSASSS after multivariate adjustment for age and disease duration ( = 0.70,  < .01). Patients with spinal bone bridge have higher levels of melatonin than those without spinal bone bridge [16.69 (4.65, 41.10) pg/ml vs. 7.43 (3.29, 15.30) pg/ml,  = .03]. The multiple linear regression analysis found that melatonin was a risk factor for spinal bone formation ( = 0.35,  < .05). Additionally, melatonin correlated positively with osteocalcin ( = 0.34,  = .04) and IL-1β ( = 0.39,  = .04) in AS. Melatonin is increased in AS patients, especially in patients with spinal bone bridge. It suggests that melatonin may play an important role in the pathological osteogenesis of AS.