Polyangiitis under the microscope

Microscopic polyangiitis (MPA) is a systemic necrotizing vasculitis mainly involving small blood vessels, which can invade the small arteries, microarteries, capillaries and veins of the kidneys, skin and lungs. Often manifested as necrotizing glomerulonephritis and pulmonary capillary vasculitis. In 1948, Davson et al. First proposed that there is a subtype characterized by segmental necrotizing glomerulonephritis in nodular polyarteritis, which is called microscopic polyarteritis because it mainly Involving small blood vessels, including veins, is now commonly referred to as microscopic polyangiitis. The American Academy of Rheumatology classification of vasculitis in 1990 did not list MPA separately. Therefore, most of the previous polyangiitis under the microscope belonged to polyarteritis nodosa (PAN), and very few belonged to Wegener. Granuloma (Wegeners granulomatosis, WG). At present, it is generally believed that polyangiitis under the microscope is an independent systemic necrotizing vasculitis, with little or no immune complex deposition, and necrotizing glomerulonephritis and capillaritis of the lung are common. Chapel Hill conference in 1993 defined polyangiitis under the microscope as a type of necrotizing vasculitis that mainly involves small blood vessels (such as capillaries, veins or arteries) without immune complex deposition. The difference between PAN and MPA is that the former lacks vasculitis of small blood vessels, including arterioles, capillaries, and small veins. In view of MPA, WG and CSS (Churg-Strauss syndrome), three types of vasculitis have similar characteristics of ANCA-positive and lack of immune complex deposition. They are often referred to as ANCA-associated vasculitis.