Microscopic polyangiitis

Last revised by Jeremy Jones on 20 Apr 2023

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

It typically affects middle-aged individuals.

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

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 localization in vessel walls which distinguishes MPA from immune complex-mediated small vessel vasculitis (e.g. Henoch-Schonlein purpura and cryoglobulinaemic vasculitis)

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

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

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

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 tumor necrosis factor-alpha blockers rituximab, 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.

It is thought to have been initially described by Friedrich Wohlwill (1881-1958), a German physician, in 1923 10.

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

For lung involvement consider:

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