Systemic lupus erythematosus (SLE) pneumonitis mimicking swine influenza pneumonia during the swine influenza (H1N1) pandemic.

BACKGROUND: We present a young woman with a negative medical history who presented with acute systemic lupus erythematosus (SLE) pneumonitis mimicking swine influenza (H1N1) pneumonia. Because this case occurred during the H1N1 pandemic, the initial diagnostic impression was of H1N1 pneumonia. METHODS: Although her clinical and laboratory findings were consistent with the diagnosis of H1N1 pneumonia, e.g., fever, sore throat, dry cough, arthralgias, myalgias, thrombocytopenia, relative lymphopenia, and elevated serum transaminases, some findings suggested an alternate diagnosis, e.g., leukopenia, a highly elevated erythrocyte sedimentation rate, highly elevated serum ferritin levels, elevated antinuclear antibody (ANA) levels, and double-stranded (DS) DNA titers. Her chest x-ray showed an accentuation of basilar lung markings, with a small pleural effusion similar to the chest x-ray findings of early H1N1 pneumonia. Initially, her headaches were thought to be related to central nervous system manifestations of H1N1. RESULTS: After laboratory test results demonstrated elevated ANA and anti-DS DNA titers, she was diagnosed with acute SLE pneumonitis. The take-home lesson for clinicians is that other infectious diseases, e.g., human parainfluenza virus or Legionnaires' disease, can mimic H1N1 pneumonia during an influenza pandemic. Excluding asthma, congestive heart failure, exacerbations of acute bronchitis, chronic obstructive pulmonary disorder, and pulmonary interstitial disease, noninfectious mimics of H1N1 are extremely rare. CONCLUSION: To the best of our knowledge, this is the first reported case of de novo SLE pneumonitis mimicking H1N1 pneumonia during the swine influenza pandemic.