Serum interleukin-6 receptor in polymyalgia rheumatica: A potential marker of relapse/recurrence risk

Objective. To investigate the modulation of systemic levels of soluble interleukin-6 receptor (sIL-6R) and soluble gp130 (sgp130) in untreated and treated polymyalgia rheumatica (PMR) patients during a followup period of at least 24 months in order to evaluate the relationship of these molecules with clinical outcome and their feasibility to provide a prognostic tool in clinical practice. Methods. We analyzed sIL-6R and sgp130 serum levels in 93 PMR patients, and 46 age-matched normal controls, at disease onset and at 1, 3, 6, 12, and 24 months of followup during corticosteroid therapy by enzyme-linked immunosorbent assay. Results. No difference in sIL-6R and sgp130 levels was observed between PMR patients and normal controls at disease onset or during followup. A significant correlation was found between the number of relapses and sIL-6R concentrations at baseline and after 1, 3, and 12 months of therapy. No correlation was found between sgp130 levels and the number of relapses. Cox multivariate analysis indicated that the best model for predicting relapses was identified by sIL-6R levels and the hemoglobin value at baseline. We found that high sIL-6R levels combined with low hemoglobin values resulted in a 10.1-fold increased risk of relapse. Conclusion. Our data support the identification of a potential prognostic marker of PMR outcome that might have important implications in clinical practice. Because targeting sIL-6R with blocking antibodies has proven useful in other rheumatic disorders, our results could suggest the opportunity to evaluate sIL-6R-blocking treatment in patients with PMR and elevated levels of sIL-6R at disease onset.