Acute exacerbation of interstitial lung diseases: A prospective multicenter observational study

<bold>Introduction:</bold> Acute exacerbation (AE) of interstitial lung diseases (ILDs) (AE-ILDs) was first observed in idiopathic pulmonary fibrosis (IPF), but it also occurs in other forms of ILDs. This study aimed to clarify real-world characteristics of AE-ILDs. <bold>Patients and Methods:</bold> Patients with acute deterioration of ILD (AD-ILD), defined by worsening shortness of breath and new lung abnormalities within one month, were prospectively enrolled from 24 hospitals of the NHO network goup. AD-ILD included both AE-ILD, diagnosed by Collard's criteria, and other acute conditions. <bold>Results:</bold> A total of 394 patients were analysed, including 303 diagnosed with AE and 91 with non-AE-ILD. The underlying ILDs included IPF (n = 177) and non-IPF ILDs (n=217). Among the 394 patients with AD-ILD, 303 were diagnosed with AE-ILDs, and 91 patients had non-AE-ILDs. Oxygenation deterioration, defined by Blancal, was observed in 313 patients (79.4%). Among the 303 patients with AE-ILD, 66 had triggered AE-ILDs. The AE-ILD group had a significantly lower 90-day survival rate (62.9%) than the non-AE-ILD group (83.3%, p < 0.001, log-rank test). The 90-day survival rates for AE-IPF (60.8%) and AE-non-IPF (64.7%) were similar (log-rank test, p = 0.806). No survival difference was observed between AE-ILD patients with or without triggering factors. Survival of AE-ILD patients with oxygenation deterioration was worse than that of those without oxygen deterioration. The survival rate of AE-ILD patients without oxygenation deterioration was similar to that of patients with non-AE-ILD. <bold>Conclusions:</bold> Prognosis of AE-ILDs was poor and similarly in IPF and in non-IPF. Oxygenation deterioration might be important for AE diagnosis.