We describe a 68-year-old man with IgG4-related kidney disease in which relatively rapidly progressive nephropathy developed during treatment for hypertension and glucose intolerance. Although a long history of untreated hypertension suggested end-stage nephrosclerosis, careful serological and radiographic examinations revealed high serum concentrations of IgG, IgE, and IgG4, severe hypocomplementemia, and multiple organ involvement including the lacrimal and submandibular glands, lymph nodes, lungs, pancreas, kidneys, and prostate, which suggested the diagnosis of IgG4-related disease. A percutaneous renal biopsy revealed IgG4-positive plasma cell-rich tubulointerstitial nephritis with fibrosis, allowing a definite diagnosis of IgG4-related kidney disease. Administration of prednisolone 30 mg/day dramatically improved the renal function, swelling of various organs, and abnormal serological state including hypocomplementemia. Recurrence with progression of renal dysfunction and hypocomplementemia during glucocorticoid tapering was observed, and the renal function improved again by increasing the dose of glucocorticoid. The clinical course of this case highlighted the importance of serological and diagnostic imaging screening to facilitate the earliest possible diagnosis and therapeutic intervention, as well as the usefulness of follow-up of the complement titer as a therapeutic marker.
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