Transformation from tubulointerstitial nephritis to crescentic glomerulonephritis: an unusual presentation of ANCA-associated renal vasculitis.

A 44-year-old man with acute renal failure and antineutrophil cytoplasmic antibodies (ANCA) positivity was described. The first renal biopsy specimen showed tubulointerstitial nephritis (TIN) with normal glomeruli. However, delayed recovery of renal function with low-dose steroid treatment for TIN prompted a second renal biopsy 1 month later; and the specimen demonstrated a dramatically different morphology, with necrotizing and crescentic glomerulonephritis. Improvement in renal function occurred, together with reduction of ANCA titers, following intensive immunosuppressive therapy. This case illustrates an unusual presentation of TIN in ANCA-associated renal vasculitis. The possible pathogenetic mechanism are discussed.