What features distinguish the small vessel vasculitides?
The small vessel vasculitides have significant overlap in their manifestations and affect small vessels including intraparenchymal arteries, arterioles, capillaries, and venules.
Features that distinguish them have been used in proposed classification schemes:
GPA is associated with granulomatous inflammation that may affect the lower and upper respiratory tracts, often causing sinus symptoms, in addition to glomerulonephritis.
MPA also leads to necrotizing vasculitis of small vessels and often leads to glomerulonephritis as well as pulmonary capillaritis and pulmonary hemorrhage. Notably, granulomatous inflammation is absent .
EGPA also demonstrates granulomatous inflammation of small- and medium-sized vessels and involves the respiratory tract. The distinguishing histologic feature is that of eosinophil-rich inflammation with peripheral eosinophilia. Patients also have associated asthma. ANCA are found in about 40% of patients with EGPA compared with about 90% of patients with MPA, GPA, or pauci-immune NCGN.
IgA vasculitis (Henoch-Schölein purpura) demonstrates IgA1 immune deposits with vasculitis affecting small vessels. In addition to glomeruli, skin and gastrointestinal involvement are common. Patients often have arthralgias or arthritis.
Cryoglobulinemic vasculitis leads to skin and glomerular lesions with cryoglobulin immune deposits in affected small vessels. Neurologic involvement may also occur. Cryoglobulins may be present in serum.
