• Tomoyuki Fujisawa, Hironao Hozumi, Hideki Yasui, Yuzo Suzuki, Masato Karayama, Kazuki Furuhashi, Noriyuki Enomoto, Yutaro Nakamura, Naoki Inui, and Takafumi Suda.
• From the Second Division, Department of Internal Medicine, and the Department of Clinical Pharmacology and Therapeutics, Hamamatsu University School of Medicine, Hamamatsu, Japan. fujisawa@hama-med.ac.jp.
• J Rheumatol. 2019 Aug 1; 46 (8): 935-942.

ObjectiveTo assess prognostic factors of antimelanoma differentiation-associated gene 5 antibody (anti-MDA5)-positive dermatomyositis/clinically amyopathic DM-associated interstitial lung disease (DM/CADM-ILD) and evaluate the use of serum chitotriosidase, a marker for macrophage activation, as a potential biomarker in anti-MDA5-positive DM/CADM-ILD.MethodsThis retrospective study included 30 patients with anti-MDA5-positive DM/CADM-ILD. The clinical characteristics and laboratory findings at the time of diagnosis were analyzed. Serum chitotriosidase levels were measured in the 30 patients, in 21 healthy controls, and in 25 patients with anti-aminoacyl-tRNA synthetase antibody-positive (anti-ARS)-polymyositis (PM)/DM/CADM-ILD, and the potential of serum chitotriosidase as a prognostic biomarker in anti-MDA5-positive DM/CADM-ILD was assessed.ResultsThe median serum chitotriosidase level in patients with anti-MDA5-positive DM/CADM-ILD was 17.3 ng/ml, which was higher than that in healthy controls and anti-ARS-PM/DM/CADM-ILD (2.0 and 8.9 ng/ml, respectively). Of the 30 patients, 10 died of respiratory failure associated with DM/CADM-ILD deterioration. Cox hazard analysis demonstrated that higher serum chitotriosidase level and lower PaO2 value were significant predictors of a poor outcome. Using optimal cutoff levels according to receiver-operating characteristic curve analyses, chitotriosidase ≥ 23.5 ng/ml, ferritin ≥ 800 ng/ml, and Krebs von den Lungen-6 ≥ 720 U/ml were significantly associated with a poor prognosis. Serum chitotriosidase levels were negatively correlated with PaO2 and percentage predicted forced vital capacity. The survival rate was significantly poorer in patients with high chitotriosidase levels (≥ 23.5 ng/ml) than in those with low chitotriosidase levels (< 23.5 ng/ml).ConclusionSerum chitotriosidase may be a potential biomarker for predicting a poor prognosis in patients with anti-MDA5-positive DM/CADM-ILD.

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