A 40-year-old female was admitted with right chest pain. SLE was abscent from her past history, although she complained of polyarthralgia in winter. Atypical pneumonia/pleuritis was suspected by chest X-ray film, showing a nodular shadow in the right lower field and moderate pleural effusion. Chlamydia pneumonia was diagnosed by elevated anti-C. psittsci antibody, while characteristics of pleural fluid revealed serositis accompained by SLE because of the high titered anti-DNA antibody and the low titered complement. She was cured by clarithromycin and subsequent administration of prednisolon and cyclophosphamide.
