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Pulmonary Pathology Online

Pathology of Microscopic Polyangiitis (Polyarteritis)

Dr Sampurna Roy MD  





Microscopic polyangiitis was initially considered a "microscopic" form of polyarteritis nodosa and was not definitively distinguished from it until the Chapel Hill nomenclature (1994).

Microscopic polyangiitis is a systemic necrotizing vasculitis of small vessels. Its typical clinical manifestations are rapidly progressive glomerulonephritis and alveolar hemorrhage.

In microscopic polyangiitis (MPA), the vascular changes are very similar to those seen in Wegener's Granulomatosis  but granulomatous inflammation is absent.

It is distinguished from polyarteritis nodosa by the size of vessels involved:polyarteritis nodosa by definition does not involve vessels smaller than arteries.

About 80% of patients with MPA have serum ANCA , usually pANCA.

Approximately 90% of patients have glomerulonephritis, and MPA is the commonest cause of the pulmonary-renal syndrome.

Other organs involved include skin, skeletal muscle, peripheral nerve and gastrointestinal system.

Pulmonary capillaritis is identified in biopsies by the presence of blood in alveolar spaces together with necrotizing capillaritis involving alveolar walls.

These show lack of continuity due to necrosis and are outlined by neutrophils and neutrophilic debris.

Fibrinoid necrosis is difficult to identify but may be seen in arterioles and venules.

Alveolar capillaritis causes severe and often life-threatening pulmonary hemorrhage and a patient with pulmonary infiltrates, hemoptysis and necrotizing segmental glomerulonephritis with crescents may have either MPA or WG.

The distinction rests on the presence of granulomatous inflammation and the type of ANCA present, but therapy should not be delayed while a biopsy diagnosis is awaited.

Microscopic polyangiitis/polyarteritis may be a dynamic condition with clinical and histopathological features evolving over time to other forms of small vessel vasculitis, mainly WG, thereby meaning that follow up would be necessary not only to control a given patient but also to make a final diagnosis.

The vasculitis in patients with microscopic polyangiitis is pathologically indistinguishable from the vasculitis of Wegener's Granulomatosis  and Churg-Strauss Syndrome.

Granulomatous inflammation distinguishes Wegener's granulomatosis from microscopic polyangiitis.

Asthma and eosinophilia distinguish Churg-Strauss syndrome from microscopic polyangiitis.

Microscopic polyangiitis, Wegener's granulomatosis, and Churg-Strauss syndrome are all associated with circulating antineutrophil cytoplasmic autoantibodies. 

Further reading:

Nomenclature of systemic vasculitides. Proposal of an international consensus conference.

Microscopic polyangiitis with ocular manifestations as the initial presenting sign.

Microscopic polyangiitis presenting as a "pulmonary-muscle" syndrome: is subclinical alveolar hemorrhage the mechanism of pulmonary fibrosis?

Microscopic polyangiitis associated with primary biliary cirrhosis: a causal or casual association?

Increased serum vascular endothelial growth factor levels in microscopic poly angiitis with pulmonary involvement.

Childhood microscopic polyangiitis associated with MPO-ANCA.

Pulmonary interstitial fibrosis as a presenting manifestation in perinuclear antineutrophilic cytoplasmic antibody microscopic polyangiitis.

Development of microscopic polyangiitis-related pulmonary fibrosis in a patient with autoimmune pulmonary alveolar proteinosis.

Development of microscopic polyangiitis in patients with chronic airway disease.

Microscopic polyangiitis (microscopic polyarteritis)

Two patients with microscopic polyangiitis and unusual pulmonary manifestation.

Microscopic polyangiitis associated with diffuse panbronchiolitis.




Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)

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