Features that overlap:
(1) size of vessels involved (PAN usually involves medium-sized arteries but may involve small; mPA usually involves small arteries but may involve medium)
(2) ANCA positivity (PAN is usually ANCA negative but may be positive; mPA is usually ANCA positive but may be negative)
(3) clinical signs and symptoms (gastrointestinal tract involvement, skin lesions, etc)
Features indicative of microscopic polyangiitis
(1) vasculitis involving arterioles, capillaries and/or venules
(2) pulmonary hemorrhage and/or pulmonary capillaritis
(3) necrotizing glomerulonephritis with no or rare immune deposits
Features indicative of polyarteritis nodosa:
(1) presence of chronic hepatitis B antigenemia
(2) arteriographic lesions, including microaneurysms
where:
• A few patients with PAN may develop a nephrotic syndrome secondary to a membranous or membranoproliferative glomerulonephritis.
• Microaneurysms may rarely be present in mPA.
