[The 485th case: fever of undetermined origin and hypoxemia].

A 49-year-old male was admitted to Peking Union Medical College Hospital presented with fever for more than half a year. The patient was diagnosed as Sjogren's syndrome at local hospital. After oral prednisone 60 mg per day was given, the fever alleviated, but recurred after prednisone tapered to 40 mg/d. Both blood culture and stool culture were positive for Salmonella enteritidis. Antibiotics including ceftazidime, ceftriaxone, cilastatin-imipenem were sequentially administrated for 4 weeks, yet not effective. Although there were not respiratory symptoms or certain abnormalities on high-resolution chest CT, arterial blood gas indicated hypoxemia. Serum lactate dehydrogenase and ß2 micro-globulin were elevated, and the lung function test demonstrated significant impairment of diffusion function. Positron emission tomography-computed tomography (PET/CT)scan suggested that high fluorodeoxyglucose uptake was diffusely seen in both lungs. The patient was finally diagnosed as pulmonary intravascular large B-cell lymphoma (IVLBCL) by transbronchial lung biopsy. This case aims to emphasize the differentiation diagnoses of pulmonary intravascular lymphoma from common situations.