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Microscopic polyangiitis (MPA)

What is microscopic polyangiitis?

Microscopic polyangiitis (MPA) is a rare form of vasculitis which mainly affects small and medium-sized blood vessels. The disease commonly affects the lungs, kidneys, skin, ears, and nervous system but can affect most parts of the body including the eyes, joints, and brain. Severe damage to these organs can occur. Involvement and severity varies widely from patient to patient, from mild to life-threatening.

Who gets microscopic polyangiitis?

MPA can affect children and adults and occurs in both men and women. Although Caucasians are affected more often, people all over the world can get MPA.

What causes microscopic polyangiitis?

Microscopic polyangiitis is thought to be an auto-immune disease for which there is no known cause.

How is microscopic polyangiitis diagnosed?

The diagnosis of MPA made by combining clinical features with laboratory tests (including tests for ANCA) and tissue biopsies.

What is the treatment for microscopic polyangiitis?

Like granulomatosis with polyangiitis (Wegener's) (GPA), treatment of MPA usually includes a combination of glucocorticoids and an immunosuppressive drug such as cyclophosphamide, methotrexate, or azathioprine. If diagnosed early, treatment can bring about early remission and prevent organ failure. It can be a chronic disease. While remission of symptoms is usually achieved, the relapse rate remains high.

What are the chances that my newly diagnosed vasculitis will relapse?

Reported relapse rates in microscopic polyangiitis have ranged from 40-60%.

What is the difference between ANCA and ANA?

Both are blood tests used by doctors to help in the diagnosis of autoimmune disease. Antineutrophil cytoplasmic antibody (ANCA) is blood test commonly elevated in patients with diseases such granulomatosis with polyangiitis, microscopic polyangiitis, and Eosinophilic Granulomatosis with Polyangiitis (Churg-Strauss). Antinuclear antibody (ANA) is a blood test most often elevated in patients with systemic lupus erythematosus (“lupus”), Sjogren syndrome, scleroderma, and other types of autoimmune diseases.

In ANCA-associated vasculitis, including microscopic polyangiitis (MPA), do increases in the ANCA tests predict disease relapse?

A general and over-simplified answer is: no. This answer is based on the statistical analysis of large groups of patients followed prospectively in clinical trials. The results from these studies have led to the general opinion held by vasculitis experts that treatment decisions should not be made based on changes in ANCA levels alone.

There are some patients, however, for whom ANCA levels track the disease activity very well. In these patients, ANCA increases do predict relapses. To know how ANCA levels relate to disease activity in individual patients, their ANCA levels need to be monitored over time.

It should also be noted that there are different ways of measuring ANCA levels. To follow serial ANCA levels they need to be measured by the same method to be able to make comparisons.