[Vasculitis of the kidney]

Panarteritis nodosa, Wegener's granulomatosis and idiopathic necrotizing glomerulonephritis, regarded by some as a vasculitis restricted to the glomerulus, are those forms of primary vasculitis most often encountered in renal biopsy. The histopathologic differential diagnosis can be difficult and has to rely on the finding of vascular inflammation in preglomerular vessels and of granulomata. In a majority of renal biopsies only a necrotizing and crescentic glomerulonephritis without inflammation of arteries or arterioles can be seen. Also the clinical manifestation of these three diseases can be very similar. A new impetus for the differential diagnosis of vasculitis was the discovery of antineutrophilic cytoplasmic antibodies (ANCA). In alcohol fixed leukocytes a cytoplasmic immunofluorescence (c-ANCA) represents an autoantibody to a serine protease of 29 kD - probably Protease 3-, and a perinuclear stain (p-ANCA), often a reaction against myeloperoxidase. ANCA antibodies seem to be a useful marker for the diagnosis of Wegener's granulomatosis, although ANCA positive tests have also been obtained in microscopic panarteritis nodosa and seemingly even in lupus nephritis. ANCA autoantibodies apparently are a reliable parameter to assess activity of the vasculitic process, and may thus be helpful in therapeutic decisions. Despite of current aggressive immunosuppressive therapy long term survival of patients or their kidneys still is rather bleak, in case a severe renal vasculitic process is diagnosed. Extracapillary proliferation (crescents) in more than 50% of glomeruli is also associated with an increased mortality.