pauciimmune

Pauciimmune is a histopathological term used to describe tissues with little or no immune complex deposition. In nephrology and nephropathology, it is most often used to characterize a form of necrotizing small-vessel vasculitis in which immunofluorescence shows minimal or absent IgG, IgA, IgM, and C3 deposition in the glomeruli, and electron microscopy shows few or no immune complexes. The term is commonly applied to pauci-immune crescentic glomerulonephritis, a feature of ANCA-associated vasculitis (AAV), including granulomatosis with polyangiitis (GPA, Wegener), microscopic polyangiitis (MPA), and eosinophilic granulomatosis with polyangiitis (EGPA).

AAV is typically associated with antibodies against neutrophil cytoplasmic antigens (ANCA), especially PR3-ANCA (c-ANCA) and MPO-ANCA (p-ANCA). The pathogenesis involves ANCA-mediated neutrophil activation leading to small-vessel vasculitis with tissue necrosis, rather than immune-complex–driven injury.

Diagnosis: pauciimmune pattern on renal biopsy helps distinguish AAV from immune complex GN (lupus GN, IgA nephropathy) and anti-GBM disease, which shows linear IgG deposition. Clinically, patients may have renal impairment and/or pulmonary involvement; serology for ANCAs supports diagnosis, but biopsy is definitive.

Treatment is immunosuppression (e.g., corticosteroids plus cyclophosphamide or rituximab); plasmapheresis may be used in select severe cases.

Prognosis: outcomes depend on organ involvement and treatment response.