Viral Pneumonia Requiring Differentiation from Acute and Progressive Diffuse Interstitial Lung Diseases.

Objective The clinical characteristics and chest imaging findings of viral pneumonia and several interstitial lung diseases (ILDs) overlap, and viral pneumonia may be underrecognized and misdiagnosed as certain ILDs. To clarify the frequency of viral pneumonia among patients with acute progressive clinical courses that required a differential diagnosis between ILDs and pneumonia, and to determine the most frequent ILDs misdiagnosed in cases of viral pneumonia. Patients and Methods We retrospectively analyzed patients hospitalized from 2010 to 2017 with an acute clinical course (≤30 days) who underwent bronchoalveolar lavage (BAL) for the differential diagnosis of infection and ILDs. We performed a multiplex PCR for respiratory viruses using the patients' preserved BAL fluid. The final diagnosis was made by a multidisciplinary approach and after considering the PCR results. The diagnosis at discharge was compared to the final diagnosis. Results Among the 109 patients, 53 were diagnosed with viral pneumonia. Viral pneumonia and other diseases showed some differences in symptoms and laboratory data; however, the differences were small or overlapped. Viral pneumonia was misdiagnosed on discharge as acute fibrinous organizing pneumonia, cryptogenic organizing pneumonia, or chronic eosinophilic pneumonia (AFOP/COP/CEP) (n=22), acute interstitial pneumonia (n=5), connective tissue disease-related ILDs (n=3), unclassifiable interstitial pneumonia (n=2), drug-induced ILD (n=1), and pneumonia (n=20). Conclusion Approximately half of the patients who underwent BAL had viral pneumonia. The most common ILD-related misdiagnoses were AFOP/COP/CEP. Differences in symptoms and laboratory findings between viral pneumonia and other diseases were small, and viral pneumonia should be included in the differential diagnosis when physicians encounter cases in which the abovementioned ILDs are suspected.