2020 Dec 14. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan–.
Microscopic polyangiitis is a small vessel necrotizing vasculitis, a part of a large spectrum of disorders termed as anti-neutrophil-cytoplasmic-antibody (ANCA)-associated vasculitides (AAV). This umbrella term includes granulomatosis with polyangiitis, microscopic polyangiitis (MPA), eosinophilic granulomatosis with polyangiitis (EGPA or Churg-Strauss disease), and renal limited vasculitis (RLV). This classification of vasculitides based on the type of vessels involved and the underlying etiology was first laid down by the International Chapel Hill Convention Conference on the Nomenclature of Vasculitides (CHCC 2012).
The term microscopic polyarteritis was introduced in the literature by Davson in 1948 to describe the pattern of glomerulonephritis seen in patients of polyarteritis nodosa. It was later described as a pattern of necrotizing vasculitis, without immune complex deposition, affecting small vessels such as the capillaries, venules, and arterioles. The disease commonly involves glomerulonephritis, pulmonary capillaritis, and other systemic capillary beds. It shows considerable overlap with granulomatosis with polyangiitis. The absence of granulomatous inflammation involving the upper respiratory tract and the presence of pulmonary capillaritis is said to differentiate MPA from GPA. MPA is also included in a group of disorders termed pulmonary-renal syndrome, which includes MPA, GPA, Goodpasture disease, and systemic lupus erythematosus (SLE).