Objective: This cross-sectional study was designed to assess the clinical significance of the serum KL-6 in the diagnosis of interstitial lung disease (ILD) in patients with idiopathic inflammatory myopathy (IIM).
Methods: We measured serum KL-6 levels in 184 patients with IIM using a chemiluminescent enzyme immunoassay and compared KL-6 levels between patients with and without ILD, according to other clinical features.
Results: IIM patients with ILD had significantly higher serum KL-6 levels than those without ILD (776.5 [372.3-1378.8] vs. 297.5 [204.75-599.3] U/ml, P < 0.001). At a cut-off of 461.5 U/ml identified by ROC curve, serum KL-6 yielded a sensitivity of 70.2% and specificity of 73.9% for ILD in IIM patients. IIM patients with an elevated serum KL-6 were more likely to have clinical symptoms of mechanic's hands (P = 0.002), anti-Jo-1 antibody positivity (P = 0.021), dysphagia (P = 0.039), hoarseness (P < 0.001), and polyarthritis/polyarthralgia (P < 0.001). Significant inverse correlations were found between serum KL-6 levels and pulmonary function tests (P < 0.01), including forced vital capacity (FVC, %Pred), total lung capacity (TLC, %Pred), and diffusing capacity for carbon monoxide (DLCO, %Pred).
Conclusions: Serum KL-6 offers high sensitivity and specificity for the diagnosis of IIM-associated ILD and is inversely correlated with pulmonary function deterioration. Serum KL-6 may represent a promising biomarker for monitoring ILD severity in IIM patients.
Keywords: Dermatomyositis; Interstitial lung disease; KL-6; Polymyositis; Pulmonary function test.