A case of IgG4-related kidney disease complicated by eosinophilic lung disease.

IgG4-related disease is a systemic chronic inflammatory disorder characterized by a high blood level of IgG4 and the organ injuries by marked infiltration of IgG4-positive plasma cells and fibrosis. A 71-year-old male was hospitalized for a cough, malaise and anorexia. IgG4-related disease was suspected due to marked elevation of the serum IgG4 level. However, on lung biopsy, only eosinophil infiltration was demonstrated with no plasma cell infiltration. Otherwise abdominal contrast-enhanced CT showed mild enlargement of the bilateral kidneys and many differed contrasted areas and FDG PET-CT. Moreover, renal biopsy specimens showed typical tubulointerstitial nephritis with a large number of IgG4-positive plasma cells infiltration (the IgG4/IgG-positive cell rate, 89 %) and fibrosis. We diagnosed this patient as typical IgG4-related kidney disease. He was treated by the moderate dose of prednisolone (0.8 mg/kg/day) alone, and showed prompt response in the clinical condition, and both the lung and kidney lesions. In this case, it was useful for diagnosis of IgG4-related diseases to evaluate an image such as abdominal contrast-enhanced CT and FDG PET-CT. Our case might be one of the possible patterns of IgG4-related lung diseases. In addition, we thought that there might be an association between hypereosinophilia and IgG4-related kidney disease.