Polyarteritis (microscopic)

Microscopic polyangiitis affects the smaller arteries and is the most common form of arteritis. There may be a history of hypersensitivity to drugs or foreign proteins, and the natural history is a short duration of vasculitis in the small veins, arteries and capillaries.

• microscopic polyangiitis is characterized by (1,2,3):
  • renal disease
  • pulmonary disease
  • ANCA directed against myeloperoxidase (p-ANCA)
• characterised by (3):
  • necrotising vasculitis, with few or no immune deposits, predominantly affecting small vessels (i.e. capillaries, venules or arterioles)
  • necrotising arteritis involving small and medium arteries may be present
  • necrotising glomerulonephritis is very common
  • pulmonary capillaritis often occurs
  • granulomatous inflammation is absent

This disease is uncommon with an annual incidence depending on geographic location (varying from 2.7 to 11.6 cases per million)

• most frequent in the elderly but has a wide age range with men being affected more often than women

Management

• induction treatment for most patients with ANCA associated vasculitis (AAV) should be with cyclophosphamide or rituximab and glucocorticoids
• AAV should be considered to be a chronic disease needing long term immunosuppressive therapy
• rituximab should be considered as an alternative induction agent for those at high risk of infertility and infection
• mortality remains high, and late death is due to cardiovascular disease, infection (secondary to treatment) and malignancy

References:

1. Davies DJ. Small vessel vasculitis. Cardiovascular Pathology 2005; 14 (6): 335-346.
2. ARC Autumn 2012. Topical Reviews - ANCA-associated vasculitis; 1:1-12.
3. Yates A, Watts R. ANCA-associated vasculitis. Clinical Medicine 2017 Vol 17, No 1: 60–4.