A case of rapidly progressive IgA nephropathy after SARS-CoV-2 vaccination, successfully treated with cyclophosphamide.

A 61-year-old woman with a 10-year history of type 1 diabetes mellitus was referred to our nephrology department due to rapid kidney function deterioration. Despite good blood glucose control, her serum creatinine (Cr) concentration rose from 0.77 mg/dL to 2.40 mg/dL over one year. She had microscopic hematuria for several years, and an increase in urinary protein was observed over the past year. One month before the onset of kidney function exacerbation, she received the fourth vaccination against SARS-CoV-2. At referral, her urinary examination showed proteinuria of 4.73 g/g Cr and microscopic hematuria. MPO-ANCA, PR3-ANCA, and anti-basal membrane antibodies were negative. A kidney biopsy revealed IgA nephropathy demonstrating focal mesangioproliferative glomerulonephritis with cellular crescents (M0E1S1T0-C1). The patient underwent six courses of intravenous cyclophosphamide administration in addition to steroid pulse therapy. One year after starting the treatment, her serum Cr improved to approximately 2 mg/dL, and urinary protein decreased to 0.6 g/g Cr.