Giant Cell Arteritis : Microscopic Features

Vasculitides are a heterogenous group of disorders characterized by inflammation of blood vessel walls. Arteritis involves arteries or arterioles. When capillaries and veins are also involved, the term vasculitis or angiitis is more appropriate. The clinical presentation depends upon the location, type and caliber of the vessels involved. Due to the wide range of symptoms and signs, vasculitides are often confused with multisystem diseases. The Chapel Hill Consensus Conference nomenclature classifies vasculitides based on the caliber of the involved vessel.Large Vessel Vasculitis: This group involves aorta, aortic arch branches and the distributing arteries in the head and extremities. Main examples include Giant cell (Temporal arteritis), Takayasu arteritis and IgG4-related aortitis/periaortitis. Other conditions associated with aortitis include: rheumatoid arthritis, ankylosing spondylitis, scleroderma, granulomatosis with polyangiitis, Cogan syndrome, and Behcet disease etc. Medium Vessel Vasculitis: This group affects medium-sized muscular arteries and is characterized by fibrinoid necrosis of the arterial wall and formation of pseudoaneurysms. Examples include Kawasaki disease and Polyarteritis nodosa.Small Vessel Vasculitis: This condition involves arterioles, capillaries, and venules. It is subclassified into: 1) ANCA-mediated vasculitis, 2) Immune complex-mediated vasculitis, and 3) Direct antibody-mediated vasculitis.When no specific size vessel is involved, the term variable-vessel vasculitis is applied.