Microscopic polyangiitis

Microscopic polyangiitis (MPA) is characterized by pauci-immune, necrotizing, small vessel vasculitis without clinical or pathological evidence of granulomatous inflammation. The annual incidence in the US of MPA is 3.6 cases per million persons. Prevalence is 1-3 cases per 100,000 population. GPA and MPA, comprise a category of small vessel vasculitis related to the presence of ANCAs and are characterized by a paucity of immune deposits. MPA and GPA seem to be part of a clinical spectrum and share a number of clinical symptoms. However, an absence of granuloma formation and sparing of the upper respiratory tract are features of MPA which help to distinguish MPA from GPA. Occasionally, the two conditions are difficult to distinguish.

About Vasculitis Vasculitis is a general term referring to a heterogeneous group of diseases that are characterised by inflammatory destruction of blood vessels. The condition occurs if the immune system attacks the blood vessels and this may happen as a result of an infection, a medicine or another disease.

Vasculitis can be acute or chronic and may affect any blood vessel in the body. The inflamed blood vessels cause changes in the vessel wall, including thickening, weakening, narrowing and scarring and this can lead to serious complications damaging the body’s organs. Specific signs and symptoms depend on which organ has been damaged and the extent of the damage. The cause of many forms of vasculitis is poorly understood. There is usually an immune component, but the trigger is often not identified. In these cases, the antibody found is sometimes used in classification, as in ANCA-associated vasculitides (Anti-neutrophil cytoplasmic antibodies).

Example of ANCA-associated vasculitides are granulomatosis with polyangiitis (GPA) (previously named Wegener's granulomatosis), Churg-Strauss syndrome and microscopic polyangiitis (MPA).