Background/Purpose: Because interstitial lung disease (ILD) is one of the most critical manifestations and can be lethal in inflammatory myopathies (IM), especially amyopathic dermatomiositis (ADM), it is important to determine prognostic factors for survival. We investigated clinical features which are associated with fatal events in IM patients having ILD.

Methods: We retrospectively analyzed clinical features, laboratory and HRCT findings, pulmonary function, and therapeutic regimens with clinical outcomes in 144 patients who were diagnosed with IM at the two hospitals of Yokohama City University from 1993 to 2012. Diagnoses of IM and clinical ADM were made according to Bohan and Peter criteria and modified Sontheimer’s criteria, respectively. DM patients who did not met the ADM criteria were categorized as myopathic DM (MDM). The distribution and extent of ILD lesions were evaluated based on the percentage of the lung parenchyma involved in each of the four-divided lung zones (A to D) from upper to lower.

Results: HRCT showed ILD lesions in 83 of 144 IM patients (58%); polymyositis (PM) 18, MDM 40, ADM 25. Routine malignant screening detected cancers in 13 (16%). Twenty patients (24%) including 2 PM, 13 MDM and 5 ADM died during follow-up period (median 49 mo. (0.5-235 mo.)) due to respiratory failure (11 patients), infection (6), and malignancy (5). Of them 12 died within 7 months after the diagnosis. The levels of serum CK, P (PaO2)/F (FiO2) ratio, and PCO2 before therapy were significantly lower in non-survivors than survivors (CK; 817±1235 vs. 1809±2773, p=0.03, P/F ratio; 344±92.6 vs. 398±87, p=0.04, PCO2; 36.2±5.2 vs. 38.8±3.9, p=0.04). Moreover, high CRP (non-survivors 4.65±6.94, survivors 1.15±2.56 (p=0.04)) and high ILD scores in the upper lung field (Zone A; 1.5±1.2, 0.8±0.9 (p=0.01), Zone B; 1.8±1.4, 1.0±1.0 (p=0.01), Zone A+B; 3.3±2.5, 1.8±1.9 (p=0.01), respectively) were closely associated with lethal events (Figure). All of 9 patients who required mechanical ventilatory support died. Intensive combination immunosuppressive therapies with PSL, IVCY, and calcineurin inhibitors were conducted in 20 patients including 10 MDM, and 10 ADM patients with lower CK and hypocapnia, because they were likely to progress fatal respiratory failure rapidly as clinically ADM associated ILD. Of them, 8 non-survivors, who showed lower CO2 level at the diagnosis than survivors (32.9±3.0 vs. 36.4±4.1, p=0.076), died within short term from diagnosis (median 2 mo. (1-51 mo.)) because of respiratory failure (5 patients) and/or infection (4 patients).

Conclusion: The present study revealed that some MDM patients as well as ADM patients developed lethal ILD especially when low CK, high CRP, hypocapnia, and expanded upper lung field lesions were found. More rapid and intensive therapies including prophylactic procedures against infections are necessary to manage IM associated ILD before type I respiratory failure progresses.