Mixed Vasculitis (ANCA-Associated Vasculitis + Goodpasture's Disease): Atypical Presentation with Impure Nephrotic Syndrome

ANCA-associated vasculitis and Goodpasture's disease represent extremely severe pathologies requiring rapid management. Double-positive vasculitis is a rare entity associating both anti-glomerular basement membrane antibodies and anti-neutrophil cytoplasmic antibodies. Renal involvement in these vasculitides most often presents as rapidly progressive glomerulonephritis with rapid deterioration of renal function. We report an atypical mode of revelation of renal involvement in a case of double-positive vasculitis, manifested by an impure nephrotic syndrome. A 52-year-old patient without prior medical history presented with dyspnea and generalized edema. Laboratory investigations revealed severe anemia requiring multiple transfusions, renal failure requiring hemodialysis, proteinuria at 12 g/24h, and positive anti-glomerular basement membrane and anti-myeloperoxidase antibodies. The clinical course was complicated by pulmonary embolism, alveolar hemorrhage, septic shock, and death. Renal biopsy confirmed the diagnosis of double-positive vasculitis. This case illustrates the diagnostic and therapeutic challenges of double-positive vasculitis and highlights the possibility of atypical presentation as nephrotic syndrome rather than rapidly progressive glomerulonephritis.