Niida et al. Journal of Medical Case Reports 2011, 5:295 http://www.jmedicalcasereports.com/content/5/1/295 rate was 48 mm/hour. His ferritin level was very high (1563 ng/mL, normal range: 20 to 120). An echocardiography showed severe aortic regurgita- tion and a prolapsed aortic valve. A transesophageal echocardiography revealed two small vegetations. We initially considered that his symptoms resulted from congestive heart failure caused by infective endocarditis and so we began empirical therapy. However, antibiotics (ceftriaxone 2 g/day and gentamicin 180 mg/day) did not improve his symptoms or laboratory data after two weeks of therapy. A blood culture detected no bacteria. We ordered additional laboratory tests in accordance with the guidelines for a fever of unknown origin. The results of serological tests for Epstein-Barr virus, cytome- galovirus, and mycoplasma were negative. An evaluation of connective tissue disease was nonspecific and yielded negative results for rheumatoid factor, anti-nuclear antibo- dies, anti-DNA antibodies, and C- and P-anti-neutrophil antibodies. Although high levels (4130 U/mL, normal range: 124 to 466) of soluble interleukin-2 receptor (sIL- 2R) suggested the presence of lymphoproliferative disor- ders, a systemic CT scan using intravenous contrast revealed no lymphadenopathy. A blood gas analysis showed hypoxemia and respiratory alkalosis, pH 7.461, arterial oxygen tension (PaO2) of 74.1 Torr, arterial carbon dioxide tension (PaCO2) of 27.7 Torr, and concentration of bicarbonate (HCO3-) of 19.5 Page 2 of 5 mmol/L under room air. We performed pulmonary func- tion tests to evaluate the cause of the hypoxemia. Our patient’s forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were within normal limits. His total lung capacity was 5.65 L (100% predicted) and his residual volume was 2.41 L (125% predicted). His diffu- sion capacity (7.51 mL/minutes per mm Hg) was low (41% predicted). Our patient’s respiratory symptoms and decreased diffu- sion in the pulmonary function test indicated the necessity for further examination. However, a chest radiogram failed to demonstrate any pathological findings and an HRCT scan showed no evidence of structural abnormality in his lungs (Figure 1). Although a gallium scintigraphy showed slightly increased opacity in both lungs, it was unclear which part of his lung we should target for additional eva- luations. In contrast, FDG-PET demonstrated strong increased tracer levels in the lower dorsal lung field (Fig- ure 2). The standardized uptake values in the lung field were 5.0 at the early phase (60 minutes after injection) and 6.8 at the delayed phase (120 minutes after injection). We decided to perform TBLB from his right lower lung to explore the pathological state of his lung. TBLB materials from his right lower lung revealed a diffuse atypical lymphocyte infiltration within his alveo- lar capillary vessels (Figure 3A), and immunohistochem- ical staining identified the infiltrated cells as CD20+ Figure 1 High-resolution computed tomography image. No structural abnormality is seen in the lung field by high-resolution computed tomography.