What is Microscopic Polyangiitis?
Microscopic polyangiitis (MPA) is a small vessel vasculitis which primarily affects the arterioles (small arteries), capillaries and venules (small veins). Since patients with this condition often have a positive blood test known as an antineutrophil cytoplasmic antibody (ANCA), it is also a form of “ANCA-associated vasculitis”. Granulomatosis with polyangiitis (GPA/Wegener’s) is a related condition that shares features with MPA including the presence of ANCA.
The cause of MPA is not known. This condition can affect many organ systems in the body including the skin, nerves, lungs gastrointestinal system, lungs and joints. It is a treatable condition and the goal of therapy is to stop further damage to the organs from inflammation in the blood vessels.
Who gets Microscopic Polyangiitis?
MPA is an uncommon condition. It can occur at any age, but typically affects people in their in the fifth and sixth decades of life. Men may be affected slightly more than women. It is more commonly observed in Caucasians and is rarer in other ethnic groups.
Since MPA is a systemic disease, it can affect almost any organ system in the body. Therefore, the symptoms depend on the area involved. They can vary from person to person and not all symptoms are present in everyone with the diagnosis. People with MPA often feel sick and unwell.
Symptoms may include:
- decreased appetite
- rapid and sudden weight loss
- “flu-like” symptoms
- rashes (usually over the legs)
- muscle aches
- joint pain
- shortness of breath
- coughing up blood
- abdominal pain with food
- involvement of the nerves with new numbness, tingling or sudden loss of strength with inability to lift your foot (so called “foot drop”) or wrist (“wrist drop”)
The diagnosis of MPA requires a combination of the history, physical examination and laboratory studies. Depending on the symptoms, other tests like imaging studies or biopsies may be needed.
Blood tests in MPA often show signs and symptoms of inflammation. Your doctor will also check a urine sample along with the blood test that measures kidney function (creatinine). Microscopic evaluation of the urine sample may reveal blood that is not visible to the eye.
A blood test called antineutrophil cytoplasmic antibody (ANCA) is also checked in cases where MPA is suspected. There are two types of ANCA; c-ANCA and p-ANCA. In patients with MPA, the p-ANCA is often positive along with another antibody called myeloperoxidase (MPO). The presence of the p-ANCA and the MPO antibody are very helpful in making the diagnosis of MPA in cases where the clinical symptoms fit. However, these blood tests are not positive in all patients and sometimes other tests are needed to make the diagnosis of vasculitis.
Your doctor may also need to biopsy the skin, kidney, lung or nerve if indicated.
The treatment of MPA consists of immunosuppressive medications (medications which suppress your immune system). Treatment is divided into two stages: induction of remission and maintenance of remission. The goal of treatment is to stop the inflammation and prevent further damage to the organs.
Medicines used to treat MPA include prednisone (“steroids”) often in combination with other medications like cyclophosphamide, methotrexate, azathioprine or mycophenolate mofetil. Recently, Rituxan (rituximab) was found to be an effective treatment of this disease. It is now the first FDA-approved medication for this diagnosis.
The medications chosen to treat MPA depend on the severity of the disease, organ systems that are involved and the clinical situation. With treatment, patients often go into “remission” which is the absence of signs of the disease. Some patients may experience “relapses” or “flares” which are periods where the disease becomes active again. Patients with MPA require regular follow-up with their doctors to monitor the disease and any complications from treatment. There is no cure for this disease. Most patients will be treated for at least 1-2 years after which, depending on the clinical course, the medications may be decreased or discontinued.
There is no cure for MPA but the disease and its symptoms can be managed. The long-term prognosis depends on the severity of the organs involved. It is important to distinguish damage (irreversible changes that have occurred from the vasculitis) from active inflammation. Damage to organs like the kidneys and nerves may be irreversible. Some patients with serious kidney involvement may require hemodialysis.
The goal of treatment is to prevent further progression and damage from the disease. Most people do well with treatment but relapses can occur. Patients require close follow-up with their doctors with periodic monitoring of the disease activity which is done based on symptoms and laboratory evaluations. In addition to monitoring for disease relapses, patients also need to be monitored for side-effects or complications from the treatment.
What’s new in Microscopic Polyangiitis?
Forms of vasculitis like MPA are uncommon and likely under recognized. The symptoms can be non-specific and can result in delayed diagnosis. A high index of suspicion is essential for the prompt diagnosis and treatment of MPA which is important to prevent organ failure from the disease.
Observational cohorts of patients with this disease (where patients are followed long-term) have provided us with invaluable information on the prognosis and long-term complications of therapy. Clinical trials through multi-center and international collaborations continue to provide us with insights on how to treat this disease. Such endeavors have led to the FDA approval of Rituxan (rituximab) as the first medication to treat MPA and granulomatosis with polyangiitis (GPA/Wegener’s).
Given the relapsing nature of the disease and the need for long-term treatment, there is a need for effective therapies with less toxicity. This remains an area of active research. Other areas of research include the pathogenesis of this condition, biomarkers and prognostic markers that may help follow patients over time.
Revision: September 2012