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

Abstract

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.

Keywords: acute lung injury; interstitial pneumonia; organizing pneumonia; viral pneumonia; virus.

Figure 1.

Flow chart of the diagnosis. PCR testing was performed using bronchoalveolar lavage fluid samples from 109 patients. The diagnoses of the 109 patients on discharge included AIP (n=8), AFOP/COP/CEP (n=33), pneumonia (n=24), DILD (n=19), CTD-ILD (n=15), unclassifiable IP (n=4), AHP (n=3), AEP (n=2), and radiation-primed OP (n=1). PCR testing was positive in 60 of the patients, among whom 7 were finally re-diagnosed as having diseases other than viral pneumonia: COP (n=5), radiation-primed OP (n=1), and AEP (n=1). The final diagnosis included viral pneumonia in 53 patients and diseases other than viral pneumonia in 56 patients: unclassifiable IP (n=2); AFOP, COP, or CEP (n=11); radiation-primed OP after breast cancer (n=1); AEP (n=3); AHP (n=3); CTD-ILD [n=12; polymyositis (n=3); dermatomyositis (n=2); amyopathic dermatomyositis with MDA5 antibody (n=2); antisynthetase syndrome (n=5); and rheumatoid arthritis (n=1)], DILD (n=18), and pneumonia due to unknown pathogens (n=4). AEP: acute eosinophilic pneumonia, AFOP: acute fibrinous and organizing pneumonia, AHP: acute hypersensitivity pneumonitis, AIP: acute interstitial pneumonia, CEP: chronic eosinophilic pneumonia, COP: cryptogenic organizing pneumonia, CTD: connective tissue diseases, DILD: drug-induced-ILD, ILD: interstitial lung diseases, IP: interstitial pneumonia, OP: organizing pneumonia, PCR: polymerase chain reaction

Figure 2.

The correlation between the diagnosis on discharge and the final diagnosis based on the PCR results and the multidisciplinary diagnosis. The panels on the left side indicate the diagnosis at discharge, and those on the right side indicate the final diagnosis based on the PCR results and the multidisciplinary diagnosis. The patients with a final diagnosis of viral pneumonia were diagnosed on discharge as having cryptogenic organizing pneumonia (COP), chronic eosinophilic pneumonia (CEP) or acute fibrinous organizing pneumonia (AFOP) (n=22), acute interstitial pneumonia (AIP) (n=5), connective tissue disease (CTD) -related interstitial lung disease (ILD) (n=3), unclassified interstitial pneumonia (n=2), pneumonia (n=20), and drug-induced ILD (DILD) (n=1).

Figure 3.

The chest computed tomography findings and histologic findings of viral pneumonia. Patchy ground-glass opacities (GGOs) and nodules in a 44-year-old man with human parechovirus pneumonia (a). Bilateral GGOs and centrilobular nodules in a 72-year-old woman with mixed viral pneumonia due to respiratory syncytial virus, human parechovirus, and human parainfluenza virus (type 1) (b). Bilateral GGOs and consolidation in a 42-year-old man with mixed viral pneumonia due to influenza A virus, respiratory syncytial virus, and human parechovirus (c). Arrows indicate areas where tissue samples were obtained. Histological findings obtained via transbronchial lung biopsy (d, e) and video-assisted lung biopsy (f) showed organization and swollen pneumocytes. Histological findings obtained via surgical lung biopsy showed organization, swollen pneumocytes, and pulmonary edema (f). The photos of histological specimens in panels d, e, and f respectively correspond to the patients in panels a, b, and c.

Figure 4.

The monthly distribution of the 53 patients with viral pneumonia. The bars represent the number of cases of virus infection diagnosed each month. Higher numbers of cases were diagnosed in winter and lower numbers were diagnosed in summer. RSV: respiratory syncytial virus, HPeV: human parechovirus, hMPV: human metapneumovirus, HPIV: human parainfluenza virus