Microscopic Polyangiitis
(Microscopic polyarteritis, Hypersensitivity or Leukocytoclastic
Vasculitis)
Epidemiology:
Common sites:
- skin
- mucous membranes
- lungs
- brain
- heart
- GI tract
- Kidneys
- muscle
Gross features:
- macroscopic
infarcts are uncommon
Histologic features:
- vasculitis of arterioles, capillaries, venules
- histologically similar to PAN (but muscular and
large arteries are usually spared)
- transmural inflammation of the arterial wall
with neutrophils, eosinophils,
and mononuclear cells
- fibrinoid necrosis of these areas
- thrombosed lumen
- evolves to
fibrous thickening of vessel wall without acute inflammatory infiltrate
- may involve
only a portion of vessel circumference
- predilection
for branching points and bifurcations
- all lesions are
the same age (in contrast to PAN)
- segmental fibrinoid necrosis of the media
- neutrophilic infiltration of vessel walls (may
be only change in some)
- fragmentation
of neutrophils (leukocytoclasia)
- necrotizing glomerulonephritis
(90%)
- pulmonary capillaritis is common
- no granulomatous inflammation
Immunophenotype:
Marker:
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Sensitivity:
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Specificity:
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- usually pauci-immune on immunofluorescence
- may see immunoglobulins and complement in the vascular
lesions of the skin within 24 hours of development
Molecular features:
Other features:
- p-ANCAs
in serum (70%)
- clinical
- typically
presents as palpable purpura in the skin
- hemoptysis
- arthralgia
- abdominal pain
- hematuria
- proteinuria
- hemorrhage
- muscle pain or
weakness
- may be
precipitated by drugs (penicillin), infection (Streptococci), heterologous
proteins, and tumour antigens
- most patients respond
to simply removal of offending agent
References: