Microscopic polyangiitis

**Definition:** Necrotizing vasculitis, with few or no immune deposits, predominantly affecting small vessels (i.e., capillaries, venules, or arterioles). Necrotizing arteritis involving small and medium sized arteries may be present. Necrotizing glomerulonephritis is very common. Pulmonary capillaritis often occurs. Granulomatous inflammation is absent.

**Inclusions:** - Microscopic polyarteritis

**Exclusions:** - Polyarteritis nodosa