Microscopic polyangiitis,
Wegener's granulomatosis,
Churg-Strauss syndrome, and pauci-immune necrotizing
glomerulonephritis share pathogenic, pathological, and clinical features. They all involve capillaries, venules, arterioles, and small arteries. Approximately 90% of patients have
autoantibodies either to
myeloperoxidase (MPO-
ANCA) or to
proteinase 3 (PR3-ANCA). The clinical manifestations of
ANCA-small vessel
vasculitis are protean. These can be limited to the kidney alone, or may involve the upper respiratory tract, the lungs, the skin, or a number of other organs in various combinations. The characteristic feature of the glomerular lesion is a focal necrotizing
glomerulonephritis associated with crescent formation and little or no glomerular staining for
immunoglobulin by immunofluorescence microscopy. The renal manifestations can present as a rapidly progressive
glomerulonephritis or that of a more indolent, remitting, and relapsing course that leads to substantial glomerulosclerosis. The two main prognostic markers of the long-term outcome are the presence of pulmonary
hemorrhage (which accounts for at least half of all deaths) and the entry serum
creatinine. The higher the entry serum
creatinine, the higher the risk of developing
end-stage renal disease. The treatment of
ANCA-small vessel
vasculitis and
glomerulonephritis rests primarily on the use of induction high-dose
corticosteroids and
cyclophosphamide. Patients with pulmonary
hemorrhage also benefit from
plasmapheresis. With the use of an
alkylating agent, the rate of remission is of the order of 75%, but relapses occur in about 30% of patients who achieve a remission, and in about 17% of patients after
renal transplantation. Despite the improved outcome of patients with
ANCA vasculitis in the recent decade, their long-term prognosis continues to be primarily determined by a rapid diagnosis, and the prompt institution of
therapy.