What is Microscopic Polyangiitis?
Microscopic polyangiitis (MPA) is a rare autoimmune disease that causes inflammation of small blood vessels, a condition known as vasculitis. This inflammation can restrict blood flow and damage vital organs such as the kidneys, lungs, nerves, and skin.
What Causes Microscopic Polyangiitis?
The exact cause of microscopic polyangiitis is unknown, but it is known to be an autoimmune disorder - meaning the body’s immune system mistakenly attacks its own small blood vessels. The main factors believed to contribute to the development of MPA include the following:
- Autoimmune Reaction: The immune system produces abnormal antibodies called ANCA (antineutrophil cytoplasmic antibodies), most often MPO-ANCA (myeloperoxidase-ANCA). These antibodies activate white blood cells (neutrophils), which then attack the walls of small blood vessels, leading to inflammation and tissue damage.
- Genetic Susceptibility: Certain genetic factors may make some people more prone to autoimmune diseases like MPA.
- Environmental Triggers: Possible triggers include infections, certain medications, or chemical exposures that may provoke the immune system in genetically susceptible individuals.
- Immune Dysregulation: An imbalance or overreaction of immune cells can contribute to the persistent inflammation seen in MPA.
What are the Signs and Symptoms of Microscopic Polyangiitis?
The signs and symptoms of MPA vary depending on the organs affected, but commonly include:
- Fatigue, fever, and weight loss
- Kidney problems (blood in urine, high blood pressure, kidney failure)
- Lung symptoms such as cough, shortness of breath, or coughing up blood
- Skin rashes or purpura (small red or purple spots)
- Nerve problems like numbness, tingling, or weakness in limbs
- Joint and muscle pain
These symptoms result from inflammation and damage to small blood vessels throughout the body.
How is Microscopic Polyangiitis Diagnosed?
Microscopic polyangiitis is diagnosed through a combination of clinical evaluation, laboratory tests, and imaging studies. Doctors look for signs of small-vessel inflammation and organ involvement, especially in the kidneys and lungs. Blood tests often detect ANCA antibodies, particularly MPO-ANCA, which support the diagnosis. Additional tests, such as urinalysis, chest X-rays or CT scans, and sometimes a biopsy of affected tissue (like kidney or skin), are used to confirm vessel inflammation and rule out other causes.
How is Microscopic Polyangiitis Treated?
Microscopic polyangiitis is treated primarily with medications that suppress the immune system to control inflammation and prevent further organ damage. Treatment usually begins with corticosteroids, such as prednisone, to rapidly reduce inflammation and ease symptoms. In more severe cases, stronger immunosuppressive drugs like rituximab or cyclophosphamide are used to induce remission by halting the immune system’s attack on blood vessels. Once remission is achieved, maintenance therapy with milder agents such as azathioprine, methotrexate, or mycophenolate mofetil helps prevent relapses. In patients with severe kidney or lung involvement, plasma exchange (plasmapheresis) may be performed to remove harmful antibodies from the blood. Supportive care, including blood pressure control, infection prevention, and close monitoring for medication side effects, is also essential. With early and effective treatment, many individuals with MPA can achieve long-term remission and maintain good organ function.
