Microscopic polyangiitis

Microscopic polyangiitis (MPA) is small vessel non-granulomatous necrotising vasculitis. It most often affects venules, capillaries, arterioles, and small arteries, although it occasionally involves medium-sized arteries 9.

It typically affects middle aged individuals.

Distribution

This condition can affect multiple organ systems. Common sites of involvement are

  • kidneys: necrotizing glomerulonephritis (present in ~90% of cases 1)
  • lungs: pulmonary capillitis
  • skin: purpura
  • gastrointestinal tract 

It is histologically very similar to polyarteritis nodosa except for involvement of vessels smaller than arteries (e.g. arterioles, venules, capillaries) 

There is an absence or paucity of immunoglobulin localisation in vessel walls which distinguishes MPA from immune complex-mediated small vessel vasculitis (e.g. Henoch-Schonlein purpura and cryoglobulinaemic vasculitis)

Markers
  • pANCA -positive in a significant (~70-90%) proportion of cases
Subtypes

Some classify two conditions as organ specific subsets of this condition 7 :

Pulmonary involvement

There can be a spectrum of findings which typically include pulmonary haemorrhage:

Other described manifestations (which are non-specific as individual features) include 9 :

Treatment options in severe forms usually include methylprednisolone +/- cyclophosphamide. Other management options include tumour necrosis factor-alpha blockers  ituximab, and nonpharmacologic modalities such as plasmapheresis and ventilatory management 9.

With treatment there is often complete remission of the disease in a majority of cases.

The differential can be broad dependant on the type of manifestations and feature.

For lung involvement consider:

It is thought to have been initially described by Friedrich Wohlwill in 1923 10.

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Article information

rID: 10937
System: Vascular
Tag: cases
Synonyms or Alternate Spellings:
  • Microscopic polyangitiis (MPA)
  • microscopic polyangiitis (MPA)
  • MPA
  • Microscopic polyarteritis

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