A 37-year-old Japanese man with a 4-month history of fever, cough, and dyspnea with abnormal chest X-ray findings was referred to a respirologist. He had no past history, including allergic diseases, asbestos exposure or recent trauma, and was on no regular medications, including dietary supplements. He had never eaten raw meat or freshwater fish. On physical examination, his temperature was 37.8  C, and respiratory sounds were decreased on the left side, with no abnormal respiratory sounds. He had no skin rash, bruises, or sensorimotor disorders. Chest radiography showed decreased permeability in the left lower lung field (Fig. 1a), and dynamic chest computed tomography showed a pleural effusion with passive atelectasis and pleural thickening on the left side (Fig. 1b and c). Thrombosis in the pulmonary artery and other abnormalities were not observed. On laboratory examination of the pleural effusion, the white blood cell count was 3200/muL, with 68.0% eosinophils, and total protein was 4.8 g/dL, albumin was 2.8 g/dL, and lactate dehydrogenase was 796 IU/L, indicating an exudative pleural effusion with no malignant cells on cytology and no detection of pathogens, including tuberculosis. Adenosine deaminase was 26.8 IU/L. These results were the same on examination of his other pleural effusion specimen. Blood tests showed a white blood cell count of 14,900/muL, and eosinophils were 68.0%, with no abnormal lymphocytes or hemocytoblasts. Total IgE was 730 IU/mL, and C-reactive protein was 1.57 mg/dL. Other results including liver enzymes, rheumatoid factor, antinuclear antibody, anti-neutrophil cytoplasmic antibody, and urinalysis were normal. Parasite IgG in serum, and examinations for helminth eggs were negative in stool and the pleural effusion. A thoracoscopic pleural biopsy was performed, and eosinophilic infiltration with inflammatory granulation tissue was seen without fibrinoid necrosis or malignant cells (Fig. 2a). To rule out a myeloproliferative disorder, a bone marrow biopsy was performed, and normocellular marrow with 10% eosinophils in nucleated cells, with no maturity disorder of granulocytes and no increase of hemocytoblasts, was seen (Fig. 2b). Philadelphia chromosome, FIP1-like-1 (FIP1L1) - platelet derived growth factor receptor alpha (PDGFRA) fusion gene, platelet derived growth factor receptor beta (PDGFRB), and fibroblast growth factor receptor 1 (FGFR1) were not detected. A diagnosis of idiopathic eosinophilic pleurisy was made, and the patient was treated with prednisolone 0.5 mg/kg/day with gradual tapering. After treatment, the fever, cough, and dyspnea resolved along with a decrease of blood eosinophils. His pleural effusion disappeared 3 months after treatment (Fig. 3a). Currently, he has had no recurrence for 10 months on treatment with 5 mg/day of prednisolone.
Findings on chest X-ray and dynamic computed tomography (CT) before corticosteroid treatment. (b, c) Dynamic chest CT shows a pleural effusion with passive atelectasis and pleural thickness on the left side.