Microscopic Polyangiitis

Microscopic Polyangiits (MPA) is a very rare and serious disease that causes inflammation of the small blood vessels. This can impact tissues and organs throughout the body and cause a wide variety of symptoms.

Microscopic Polyangiitis belongs to a family of arthritic diseases called vasculitis. The word vasculitis means inflammation of blood vessels. The most common affected by Microscopic Polyangiitis include the skin, joints, nerves, and kidneys.

Early diagnosis and medical therapy are essential for managing Microscopic Polyangiitis.

Autoimmune Disease

It is not known what causes Microscopic Polyangiitis but it is thought to be an autoimmune disease which occurs when the body’s immune system attacks its own healthy cells and tissues. The reasons why the body might start attacking its small blood vessels is not well understood.

Who Gets Microscopic Polyangiitis

Microscopic Polyangiitis can affect anyone but it is more common in younger and middle-aged people.

Understanding Microscopic Polyangiitis


Flu-Like Symptoms

The first signs of Microscopic Polyangiitis are similar to the flu. People start feeling unwell and commonly have a fever, achiness, malaise and weight loss.

These symptoms can last for some time. As these symptoms are common to many diseases, it can be difficult to diagnosein its early stages.

Other symptoms depend on which organs are affected.


If the kidneys are involved, a patient may experience fatigue, swelling of the legs, or shortness of breath. Kidney involvement can come on slowly or in some cases very quickly leading to rapid kidney failure.


If the lungs are involved then a patient may notice shortness of breath, a cough, or chest pain/discomfort. Lung disease is due to inflammation of the lung tissue.

In some cases, lung involvement can be very dramatic and life threatening. If lung disease is very severe there can be bleeding into the lung. In this case a patient may cough up blood.

Lung involvement is usually seen on a chest x-ray or CT-scan of the chest. It can sometimes be confused with pneumonia.


Signs of Microscopic Polyangiitis can also appear on the skin, usually as little red dots called purpura that can look like little bruises. These are usually found on the lower part of the body.


When Microscopic Polyangiitis affects the eyes, symptoms can include conjunctivitis (redness of the eye) or inflammation of other parts of the eye (uveitis).


When Microscopic Polyangiitis affects the nerves it can cause a sudden loss of strength (e.g., “foot drop” or “wrist drop”) but does not usually cause pain. Early diagnosis and treatment is important to avoid nerve damage.


When Microscopic Polyangiitis affects the joints, people can experience different symptoms. Some people have obvious swelling of the joints, which can jump around from joint to joint. In others, they ache all over.


Microscopic Polyangiitis can be difficult to diagnose because there are no symptoms that are unique to the disease. In some cases, symptoms can appear quickly. Other times, they can take a while to develop (months to years).

Microscopic Polyangiitis is usually best diagnosed by a rheumatologist (a specialist in arthritis and autoimmune disease).

To diagnose the disease, a physician will take a complete history and perform a thorough physical examination. They will usually order blood tests, x-rays and other types of tests to confirm their diagnosis and determine which organs might be affected by the disease.

In some cases a tissue biopsy is required to confirm the diagnosis. This involves taking a very small sample of tissue through a needle so it can be examined in a lab.

Common Tests to Diagnose Microscopic Polyangiitis

Blood Tests

Looking for inflammation: Microscopic Polyangiitis causes inflammation in the body so tests for inflammation are expected to have abnormal results. Common tests include a Complete Blood Count (CBC), Erythrocyte Sedimentation Rate (ESR), and C-Reactive Protein (CRP).

Looking for an immune response against white blood cells: The Anti-Neutrophil Cytoplasmic Antibody (ANCA) test looks for antibodies that attack proteins associated with neutrophils (white blood cells).

Looking at kidney function: Creatinine is a common blood test that looks at how well the kidneys are working. Abnormally high levels of creatinine can indicate a problem and can mean that the kidneys are involved.

Urine Test

Looking for kidney involvement: urinalysis testing to detect protein or blood in the urine can give a sign that the kidneys might be involved.


Looking for lung involvement: Chest x-ray and/or CT scans can help confirm if the lungs are involved.

Nerve Tests

Looking for nerve involvement: Electromyography and Nerve Conduction Studies can be performed to look for nerve involvement.


Scientists don’t know what causes Microscopic Polyangiitis, but it is thought to be an autoimmune disease. This means that it is thought that the disease is caused by the body’s immune system attacking its own blood vessels causing inflammation.

Other similar diseases in this family include granulomatosis with polyangiitis (also known as Wegener’s granulomatosis) and eosinophilic granulomatosis with polyangiitis (also known as Churg-Strauss). Every disease in this family are forms of vasculitis, which means they feature inflammation of blood vessels. of family feature inflammation of blood vessels (called vasculitis).


Microscopic Polyangiitis should be treated as early and aggressively as possible to prevent severe damage to the blood vessels, respiratory tract (including the lungs), kidneys, and other important tissues and organs.

Medications for Microscopic Polyangiitis fall into two broad groups:

  • Medications that are used initially to bring the disease under control quickly. These are called induction therapies.
  • Medications that control the disease over the long-term. These are called maintenance therapies.

Medications for Induction Therapy

Corticosteroids (prednisone), cyclophosphamide and rituximab help to rapidly reduce inflammation and control the symptoms associated with Microscopic Polyangiitis.

Once the disease is in remission (when there are no more symptoms and markers of inflammation are back to normal), induction therapies are often tapered (reduced or even stopped in some cases).

Medications for Maintenance Therapy

Azathioprine, mycophenolate mofetil or mycophenolic acid, and methotrexate are medications that are typically used for maintenance (long-term) therapy of Microscopic Polyangiitis. These medications usually take longer to begin to work. Rituximab is also being used as a chronic maintenance therapy with good success.

Maintenance medications might be overlapped with the induction therapy, but unlike induction therapies, they are usually continued over the long-term to keep the disease under control.

Corticosteroids (prednisone)

Medications like prednisone help control inflammation. They may also prevent long-term damage in some people. Prednisone is a very effective medication to control the inflammation of Microscopic Polyangiitis. In the short-term, prednisone may be given by intravenous infusion in the hospital. After a few days, this is usually switched to oral prednisone. As symptoms improve and markers of inflammation return to normal, the dose of prednisone can be gradually reduced (tapered).

When used for long periods of time, prednisone can have side effects. You should to discuss the risks and benefits of using prednisone with your doctor. Some patients who have joint involvement also benefit from cortisone injections directly into a joint. This should be discussed with your rheumatologist.


A medication called cyclophosphamide is often used with prednisone to get the disease under control. Cyclophosphamide can be given by mouth or by intravenous infusion. If there is very serious lung, kidney or nerve involvement, an intravenous infusion may be easier to administer.

Cyclophosphamide can increase your risk of infection (be careful with fevers). Cyclophosphamide can also affect your ability to have children (fertility) – this needs to be discussed with your doctor.


This is a type of therapy called a “biologic” medicine. Rituximab has been shown to be as effective as cyclophosphamide and is now approved for the treatment of microscopic polyangiitis . Although it is more expensive, it may be appealing to women of childbearing age because it does not affect fertility. Rituximab is becoming increasingly popular as a longer term choice for maintenance therapy.

Disease Modifying Anti-Rheumatic Drugs

The Disease Modifying Anti-Rheumatic Drugs (DMARDs) are medications that are typically used to treat rheumatoid arthritis. Examples that have been shown to be effective in people with Microscopic Polyangiitis include azathioprine (Imuran), methotrexate, and mycophenolate mofetil or mycophenolic acid. In many cases they are used for maintenance therapy once the disease is under control. In milder cases of Microscopic Polyangiitis they may be used initially to induce remission.

Most Disease Modifying Anti-Rheumatic Drugs take about 6-12 weeks before they begin to work. Some people might not feel any effect when they first start taking them. Even if this happens, it’s important to keep taking the medication to help keep inflammation under control and to maintain remission.