Serum KL-6 level is a prognostic marker in patients with anti-MDA5 antibody-positive dermatomyositis associated with interstitial lung disease.

Objective: This study aimed to investigate the clinical significance of Krebs von den Lungen-6 (KL-6) serum levels in patients with anti-MDA5 antibody-positive dermatomyositis (anti-MDA5+ DM) having interstitial lung disease (ILD), especially in the amyopathic DM phenotype.

Methods: The serum KL-6 level was measured using a chemiluminescence enzyme immunoassay (CLEIA) in patients with anti-MDA5+ DM, including clinically amyopathic dermatomyositis (CADM)-ILD and classic DM-ILD, and healthy donors. The baseline and post-treatment serum KL-6 levels were determined in 39 patients with CADM-ILD who experienced remission or acute exacerbation. The association between laboratory findings, high-resolution computed tomography (HRCT) scores, pulmonary function tests (PFTs), and the predictive value of baseline KL-6 level for death was analyzed.

Results: The serum KL-6 levels were significantly higher in patients with CADM-ILD (1339 ± 1329 U/mL) compared with DM-ILD (642.3 ± 498.4 U/mL) and healthy donors (162.4 ± 54.01 U/mL). The KL-6 levels correlated positively with chest HRCT scores, serum lactate dehydrogenase, serum ferritin levels, and PFTs, but not with erythrocyte sedimentation rate. During follow-up, the post-treatment serum KL-6 levels significantly reduced in the remission/stable group, but increased in the acute exacerbation group. Higher levels of ferritin and KL-6 and HRCT scores were independently associated with poor prognosis. The 1-year survival rate was significantly lower in patients with high KL-6 level than in those with low KL-6 level.

Conclusions: The serum KL-6 levels may be a useful marker for predicting and monitoring ILD in Chinese patients with anti-MDA5+ DM, especially amyopathic DM phenotype.