Background/Purpose:  Interstitial lung disease (ILD) is one of the predominant causes of death in polymyositis/dermatomyositis (PM/DM). We have already reported that low P_aCO₂ and interstitial lesions in more cranial zone of lungs are independent prognostic factors for ILD associated with PM/DM (PM/DM-ILD), and the most common causes of death in early stage are respiratory failure and infection. Here we investigated the predictive factors for complication of infection during treatment for PM/DM-ILD.

Methods:  We retrospectively analyzed clinical features, laboratory and high-resolution computed tomography (HRCT) findings at baseline, initial therapeutic regimens, clinical outcomes, and episode of serious infection of patients with PM/DM-ILD who had received initial treatment at the two hospitals belonging to Yokohama City University from 1993 to 2015. The lungs were horizontally divided into 4 zones (Zone A to D from more cranial area) in HRCT, and severity of ILD lesions were evaluated in each zone. We conducted univariate and multivariate analyses to extract risk factors for death and infection.  

Results: One hundred six patients (PM 19, DM 49, clinically amyopathic DM (CADM) 38) were recruited. The mean age was 55 +/- 14 years, and 77 (73%) were female. As initial therapies, oral prednisolone (PSL) was prescribed in all patients. Methylprednisolone (mPSL) pulse, intravenous cyclophosphamide (IVCY), and oral calcineurin inhibitor therapies were performed in 77 (73%), 43 (41%) and 73 (69%), respectively. Thirty-seven (35%) received combination therapy with IVCY and a calcineurin inhibitor. Forty patients (38%) had a total of 54 events of serious infection at 40 +/- 26 days from initiation of immunosuppressants. The foci of infection were seen most commonly in lung (bacterial pneumonia 19, pulmonary suppuration 2, pneumocystis pneumonia 9, CMV infection 15, and the others 9). Lower serum albumin level (p = 0.01), higher serum CRP, LDH, KL-6 levels (p = 0.01, p = 0.001, p = 0.01, respectively), high initial dose of PSL (p = 0.01), mPSL pulse (p = 0.02), IVCY (p < 0.001), and combined immunosuppressants (p = 0.04) were extracted as risk factors for infection by univariate analyses (Table 1). There was no significant relation between severity of ILD and infection. A multivariate logistic regression analyses revealed that the high initial dosage of PSL (p = 0.003, hazard ratio 6.21) and higher serum LDH level (p = 0.017, hazard ratio 4.08) were independent risk factors for infection. Of 11 patients, who died within 6 months, four (36%) were died of infection.

Conclusion: Although rapid and intensive therapies are required for PM/DM-associated ILD, appropriate monitoring, prophylaxis and early treatment for infection are important, especially in patients who received high-dose of initial glucocorticoid and showed higher serum LDH level.