AP-VAS 2012 case report: an atypical case of microscopic polyangiitis presenting with acute tubulointerstitial nephritis without glomerular change.

Renal involvement in myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA)-associated vasculitis is frequently characterized by focal segmental crescentic and/or necrotizing glomerulonephritis. However, a few cases of only tubulointerstitial nephritis (TIN) involvement without any apparent glomerular lesions have been reported. Here we report just such a case. A 74-year-old woman was admitted to a nearby hospital with a 2-week history of pitting edema, fever and anemia. She developed acute renal failure without proteinuria and microscopic hematuria. The urinary excretion of N-acetyl-beta-D-glucosaminidase and beta2-microglobulin concentration were 30.3 U/ml and 42270 μg/ml, respectively. Gallium-67 scintigraphy revealed abnormal concentrations on both sides of her kidneys. Her MPO-ANCA titer was 92 EU (normal range <10 EU). Skin and renal biopsies demonstrated fibrinoid vasculitis, necrotizing angiitis and TIN without glomerular change. Microscopic polyangiitis was diagnosed based on clinical and pathological criteria. No other factor that could induce TIN was detected. This case illustrates an unusual renal presentation of acute renal failure due to necrotizing arteritis and TIN, consistent with MPO-ANCA-associated vasculitis lacking crescentic glomerulonephritis. The pathogenesis is currently unclear, but the low-affinity type of MPO-ANCA was identified.