Small Vessel Vasculitis (ANCA-associated)

Necrotising polyangiitis that affects capillaries, venules, and arterioles

Aetiology

  • Usually presents 5th-7th decade

Pathophysiology

Granulomatosis with polyangiits

  • Predominantly anti-PR3 (cANCA) antibodies
  • Necrotising granulomatous inflammation
  • Lung involvement (pulmonary/renal syndrome)

Microscopic polyangiitis

  • Predominantly anti-MPO (pANCA) antibodies
  • Small vessel vasculitis with no granulomas
  • Systemic features, renal, lung, skin, GI, nerves

Eosinophilic GPA

  • Associated with asthma and eosinophilia
  • 2/3 have skin involvement, generally no kidney involvement

Clinical presentation

  • Constitutional symptoms (fever, migratory arthralgia, weight loss, anorexia, malaise) may last weeks-months before specific organ involvement
  • More specific symptoms related to organ involvement when disease progresses

Investigations

  • Urinalysis - 'active urine' (lots of blood and protein)
  • Bloods - raised inflammatory markers, AKI, anaemia
  • Immunology - ANCA
    • GPA - 95% ANCA positive, 65% anti-PR3 (cANCA)
    • MPA - 90% ANCA, 55% anti-MPO (pANCA)
    • Antibody titre is not a good marker of disease severity
  • Renal biopsy - crescentic GN, pauci-immune
    • Tend to be done less often now as other methods diagnostic

Management

  • Immunosuppression - steroids, cyclophosphamide/rituximab
  • Plasma exchange
  • Supportive - dialysis, ventilation