Background/Purpose: Because of the extremely variable incidence and outcome of interstitial lung disease (ILD) in polymyositis/dermatomyositis (PM/DM), explorationand validation of biomarkers for diagnosis, prognosis, and response to treatment is mandatory. Lung epithelium-derived proteins such as Krebs von den Lungen-6 (KL-6) and surfactant protein-D (SP-D) are widely used as serum biomarkers for ILD. However, their usefulness in patients with PM/DM is not fully established. We aimed to evaluate the usefulness of KL-6 as a biomarker of ILD with PM/DM, including in the short time course after treatment.

Methods: A total of 42 patients with active PM/DM who were admitted to our hospital from April 2010 through March 2015 were included: 22 with PM, 14 with classical DM, and 6 with clinically amyopathic dermatomyositis (CADM). PM/DM and CADM were diagnosed according to Bohan and Peter’s criteria and Sontheimer’s criteria, respectively. Overlap patients with other collagen tissue diseases were excluded to avoid potential confounding. ILD was defined as presence of a diffuse parenchymal lung disease on high-resolution CT such as reticular opacities, ground-glass opacities, and honeycombing. Clinical, radiological, and laboratory data were retrospectively collected from the medical records and statistically analyzed.

Results: Of the 42 study subjects, 30 patients had ILD on high-resolution CT: 24 with PM and classical DM, and 6 with CADM. There was no significant difference in age, sex, or disease duration between patients with and without ILD. Because most of the patients had short disease duration at study entry, % vital capacity (%VC) on admission (pre treatment) was not significantly different between patients with and without ILD (p = 0.19). However, serum KL-6 and SP-D levels were significantly higher (p < 0.01 and p = 0.01, respectively), and % diffusing capacity for carbon monoxide (%DLCO) was significantly lower (p = 0.049) in patients with ILD than those without. Levels of serum KL-6 were significantly correlated with %VC, %DLCO, and levels of serum SP-D (p < 0.01 in all comparisons) but not with alveolar-arterial oxygen difference (p = 0.39). All the patients with ILD were treated with prednisolone. In addition, cyclosporine, tacrolimus, and intravenous cyclophosphamide were administered simultaneously in 19, 6, and 8 patients, respectively. Although most of the patients showed some clinical and/or radiological improvement in 4 weeks, levels of serum KL-6 were not significantly different between those at pre treatment and at 2 or 4 weeks post treatment (p = 0.59 and 0.58, respectively).

Conclusion: The present study validated that serum KL-6 is a useful biomarker for the diagnosis of ILD associated with PM/DM. However, the levels of serum KL-6 did not respond immediately by treatment even in the cases with clinical improvement. Serum KL-6 should be used as a biomarker for ILD with PM/DM knowing its strengths and limitations.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/evaluation-of-usefulness-of-krebs-von-den-lungen-6-as-a-biomarker-of-interstitial-lung-disease-with-polymyositis-and-dermatomyositis-including-in-the-short-time-course-after-treatment/