Microscopic polyangiitis, also called microscopic polyarteritis, is a systemic necrotizing vasculitis that involves small vessels including arterioles, capillaries, and venules. Men are affected more often than women. The average age at onset is about 50 years. This condition is uncommon and its actual incidence is unknown. Typical manifestations include glomerulonephritis, pulmonary hemorrhage or infiltration, musculoskeletal pains (sometimes with synovitis), purpura, peripheral neuropathy, and abdominal pain. Systemic symptoms such as malaise, fatigue, and fever are usually present.