Microscopic polyangiitis (MPA) is a disorder that causes blood vessel inflammation (vasculitis), which can lead to organ damage. The kidneys, lungs, nerves, skin, and joints are the most commonly affected areas of the body. MPA is diagnosed in people of all ages, all ethnicities, and both genders. The cause of this disorder is unknown.

The cause of MPA is unknown. It is not contagious, does not usually run in families, and is not a form of cancer. The immune system is thought to play a critical role in the development of MPA.  It is thought that the immune system becomes overactive and causes blood vessel and tissue inflammation, which leads to organ damage. It is not known what causes the immune system to become overactive.

The symptoms of MPA depend on which blood vessels are involved and what organs in the body are affected. The most common symptoms of MPA include kidney inflammation, weight loss, skin lesions, nerve damage, and fevers. Other symptoms depending on the area(s) of the body affected may include:

• Skin-Rash
• Lungs-cough, breathing problems, spitting up blood
• Gastrointestinal-bleeding in the gastrointestinal tract, abdominal pain
• Brain/neurological-tingling, pain, weakness, loss of sensation, seizures
• Musculoskeletal-joint pain, muscle pain

The treatment of MPA is dependent on the extent of the disease, rate of progression, and the degree of inflammation. The goal of treatment is to stop organ damage that occurs as a result of MPA and involves use of medications that suppress the immune system. Treatment is typically carried out in three phases:

1. Remission induction using prednisone and cyclophosphamide. This phase usually lasts between 4 and 6 months. 
2. Remission maintenance using prednisone and replacing cyclophosphamide with other medications such as methotrexate and azathioprine. This phases usually lasts between 12 and 24 months. 
3. Treatment of relapse utilizing medications from phase one or other therapies such as intravenous immunoglobulin for resistant cases. 

The prognosis for MPA depends on the severity of the condition. Early diagnosis and prompt treatment lead to a better overall prognosis. With treatment, 75 percent of individuals achieve complete remission. After achieving remission, it is possible for MPA to recur (often referred to as a “relapse”). Relapses occur in about 30-50% of people with MPA. Achieving remission is again possible for most people with MPA.