Soluble IL-2 Receptor: A Biomarker for Assessing Myositis Activity

OBJECTIVE To evaluate the clinical significance of serum soluble IL-2R (sIL-2R) in inflammatory myopathies. METHODS Serum sIL-2R and CK levels were determined in 27 patients with IM during periods of disease exacerbation and inactive disease and were compared to 20 healthy controls and 23 controls with noninflammatory elevated CK. The performance of sIL-2R and CK tests for assessing disease activity was compared. RESULTS sIL-2R levels were increased in patients with IM. Significantly higher sIL-2R levels were detected in patients with disease exacerbation than in patients with inactive disease. In patients with IM, the sIL-2R levels correlated with the CK levels. Based on ROC analysis, diagnostic accuracy of sIL-2R and CK tests for disease activity was similar. However, when the CK threshold was defined by the upper limit of the normal, the specificity for the CK test dropped to 58%. CONCLUSION Serum sIL-2R level could be useful to distinguish disease exacerbation from damage in IM, especially in patients with persistent elevated CK levels when a clinical muscular worsening is noted. For discrimination of the disease activity, CK testing requires the use of a different threshold than the upper limit of the normal.