The transition of renal histopathology after immunosuppressive therapy in a woman with renal limited ANCA-associated vasculitis: a case report and literature review.

OBJECTIVES: The kidneys are frequently involved in antineutrophil cytoplasmic autoantibody (ANCA) associated small-vessel vasculitis (AASVV). The pathological hallmark of ANCA-associated glomerulonephritis (AAGN) is a pauci-immune necrotising crescentic glomerulonephritis. The histopathology of AAGN may change during the course of the disease as a consequence of immunosuppressive therapy. Herein, we report the pathological evolution of a case of AAGN.

METHODS: We report a female presented with renal-limited AASVV, hypocomplementemia and nephrotic syndrome. The first renal biopsy revealed "crescentic" changes at presentation, but after treatment with immunosuppressive treatment, a second renal biopsy four years later showed "mixed" changes of AAGN and immune complex deposition mimicking a mesangial proliferative glomerulonephritis. A literature review was undertaken in order to understand these transformations and factors which determine the pathological transitions.

RESULTS: AAGN is commonly described as a pauci-immune necrotising crescentic glomerulonephritis, but immune complex depositions have been frequently identified under electronic microscopy and is associated with greater levels of proteinuria. Acute lesions such as fibrinoid necrosis or glomerular crescent may completely disappear or reduce significantly after immunosuppressive therapy, but chronic changes may increase over time.

CONCLUSIONS: Based on our review and the illustration of this case, the initial histopathology of an AAGN and its active fibrinoid necrosis and cellular glomerular crescent may disappear or resolve after immunosuppressive therapy with resulting non-distinctive feature. Understanding the transition may facilitate the clinical diagnosis and provide further insight into this disease.