Marked increase in serum KL-6 and surfactant protein D levels during the first 4 weeks after treatment predicts poor prognosis in patients with active interstitial pneumonia associated with polymyositis/dermatomyositis

The aim of this study is to determine whether serum KL-6 and surfactant protein D (SP-D) levels predict the prognosis of patients with interstitial pneumonia (IP) in cases of polymyositis (PM) and dermatomyositis (DM). Fifty consecutive patients with PM (n = 17) or DM (n = 33) and active IP, 6 of whom died of respiratory failure, were enrolled in this study. Serum KL-6 and SP-D levels were measured every 2-4 weeks. Medical records were reviewed retrospectively. Univariate analyses and multivariate analyses with a logistic regression model were conducted. Serum KL-6 and SP-D levels were elevated in patients with active IP. At the time of diagnosis of active IP, the serum KL-6 level was within the normal range in 28 % of patients and the SP-D level was within the normal range in 46 % of patients. Serum KL-6 level increased up to 3 months after starting treatment and then decreased gradually to baseline, whereas SP-D level peaked within the first 4 weeks after treatment and decreased rapidly to normal levels. Patients with poor prognosis showed increases in KL-6 and SP-D levels during the first 4 weeks after treatment, which was confirmed by uni- and multivariate analyses. Comparing the marker levels at 2-4 weeks after treatment with those at 0 weeks, an increase in the ratio over 1.70 for KL-6 and over 1.75 for SP-D, and an increase in KL-6 over 850 U/ml during the first 4 weeks after treatment, were poor prognostic factors. Increases in serum KL-6 and SP-D levels during the first 4 weeks after starting therapy, but not their levels at any one time point, predict poor prognosis in patients with PM/DM. When marked increases of KL-6 and SP-D levels during the first 4 weeks are found or are predicted by serial measurement of the markers, patients have risks of poor prognosis and additional therapy should be considered.