Prognosis and treatment of myositis-associated severe interstitial lung disease: A descriptive study using a nation-wide inpatient database in Japan.

OBJECTIVES The aim of this study was to determine the prognosis, clinical course, and current management of severe interstitial lung disease (ILD) associated with myositis in Japan. METHODS We conducted a retrospective descriptive study using a nation-wide database for inpatient care of acute illness in Japan. Among a total of approximately 66 million inpatient admissions, we identified patients with severe ILD associated with polymyositis (PM) or dermatomyositis (DM) which required mechanical ventilation and methylprednisolone pulse therapy (≥1g/day usage of methylprednisolone) from July 2010 to March 2018. RESULTS We identified 155 patients with PM and 394 with DM who fulfilled the above criteria. The median age of patients was 65 years old; DM patients were significantly younger than PM patients (64 vs. 68 years old; p<0.001). The numbers of patients who were treated with calcineurin inhibitors, intravenous cyclophosphamide and Polymyxin B immobilized fiber column direct hemoperfusion (PMX-DHP) were 403 (73.4%), 318 (57.9%) and 78 (14.2%), respectively. All these treatments were given significantly more frequently to the patients with DM compared with those with PM. The uses of other treatment options were much less frequent. The median hospital days of initiating methylprednisolone pulse therapy, calcineurin inhibitors, mechanical ventilation, intravenous cyclophosphamide, PMX-DHP, and in-hospital death among patients with DM were 2, 4, 7, 8, 17, and 36, respectively. In-hospital mortality was significantly higher in patients with DM than in those with PM (76.6% vs. 56.8%, p<0.001). CONCLUSION The mortality of patients with myositis-associated severe ILD that requires mechanical ventilation is extremely high despite aggressive and prompt interventions.