Diagnosis

• measurement of ANCA titre:
  • about 50-70% of patients have ANCA (1)
    • the ANCA found in microscopic polyangiitis is usually p-ANCA (directed to myeloperoxidase (MPO)) (1) - MPO-ANCA give a perinuclear staining pattern on immunofluorescence.
      • MPO-ANCA are found in microscopic polyangiitis (70%) but PR3-ANCA (ANCA directed against proteinase 3 giving a granular cytoplasmic staining pattern on immunofluorescence) can also occur (2)
        
        
• renal biopsy
  • extracapillary glomerulonephritis is a feature in 90% of cases
    • similar findings to those seen in Wegener's granulomatosis but no granulomata are found

Notes:

• the relative prevalences of cANCA and pANCA vary with different reviews. Jennette JC et al state that serologically, the prevalence of ANCA is anti-MPO pANCA 50% and anti-PR3 cANCA 40%, with negative results in 10% (3)

Reference:

• (1) Bosch X et al. Antineutrophil cytoplasmic antibodies. The Lancet 2006;368 (9533): 404-418.
• (2) Harper L, Weidanx F. Small vessel vasculitides. Medicine 2006; 34 (11): 456-463.
• (3) Jennette JC et al. Microscopic polyangiitis (microscopic polyarteritis). Semin Diagn Pathol 2001;18: 3–13.