Wegener granulomatosis and microscopic polyangiitis

Microscopic polyangiitis (MPA) is vasculitis of small vessels. It was initially considered as a microscopic form of polyarteritis nodosa (PAN). In 1990, the American College of Rheumatology developed classification criteria for several types of systemic vasculitis but did not distinguish between polyarteritis nodosa and microscopic polyarteritis nodosa. [1] In 1994, a group of experts held an international consensus conference in Chapel Hill, North Carolina, to attempt to redefine the classification of small vessel vasculitides. [2, 3]