Dr Silke Brix
Consultant Nephrologist, Manchester University NHS Foundation Trust

Updated May 2024

What is Microscopic Polyangiitis?

Microscopic polyangiitis, MPA, is a vasculitis of the group of antineutrophil cytoplasmic antibody (ANCA) associated vasculitides typically inflaming small blood vessels. The other two recognised conditions of this disease group are granulomatosis with polyangiitis, GPA, and eosinophilic granulomatosis with polyangiitis (EGPA).

MPA clinically differs from GPA and EGPA by missing the granulomatous inflammation meaning it does not have clusters of cells that build nodules and cavities. MPA however shares the main features of inflamed vessels with the others. It causes a so-called leukocytoclastic inflammation with white blood cells bursting in small vessels destroying the vessel wall.

Who is affected?

MPA can happen at every age but it is more common in older people. The median age at diagnosis is 65 years and men are slightly more often affected. Among the ANCA vasculitides, MPA is more often found in Southern Europe and Asia while GPA is more common in Northern Europe.

What is the cause of MPA?

The cause of MPA is not yet known.

Genetic studies have revealed that some people carry gene subtypes that increase the risk of developing autoimmune diseases in general but no specific gene defects have been identified causing ANCA vasculitides. We believe that these people at risk then encounter further triggers e.g. infections, toxins, trauma etc. Consequently, they lose their tolerance to particles in their bodies and develop ANCAs. In MPA, the identified ANCA are often antibodies against myeloperoxidase (MPO). MPO ANCA activate a certain subgroup of white blood cells, the neutrophils. These activated neutrophils normally fight infections. In ANCA vasculitides, neutrophils however attach themselves to the small vessel walls and damage the vessels.

What are the symptoms?

MPA mainly affects the lungs and kidneys but might involve other organs such as skin, nerves and gut. It typically spares the ENT area often affected in GPA and EGPA.

Common symptoms are tiredness, loss of appetite, joint and muscle aches. Other symptoms depend on the organs involved and will vary markedly between patients.

Some specific symptoms are:

  • Lungs – breathlessness, wheezing, a dry cough or coughing up blood
  • Skin – rashes, ulcers, rarely necrotic (=dead tissue) wounds
  • Eyes – red and painful eyes, dry or gritty eyes, change or loss of vision
  • Nerves – tingling (=pins and needles) and numbness in fingers and toes, shooting pains along a limb, rarely symptoms of stroke and paralysis
  • Bowels – abdominal pain, diarrhoea and bleeding

Diagnosis

It is important to recognise the pattern of symptoms.

Following a clinical suspicion and a positive MPO ANCA test, the aim is to confirm the diagnosis with a tissue biopsy.  In the case of kidney disease, a kidney biopsy is often performed. Lung manifestations are more likely to be assessed with high-resolution computer tomography (HRCT) imaging only but an additional bronchoscopy with washing or biopsy might assist in checking that it is indeed vasculitis and not an infection and malignancy. Healthcare professionals will discuss patient history and test results in multidisciplinary team (MDT) meetings to decide how much diagnostics are necessary to be sure of the diagnosis to start treatment.

Treatment

Treatment has changed over the last years.

Glucocorticoids (=steroids, prednisolone) and cyclophosphamide used to be the main standard of therapy. Rituximab has shown that it is as effective as cyclophosphamide in most cases. Therefore, rituximab might be used instead or alongside cyclophosphamide. A new complement-based treatment has come on the market that might allow steroid minimisation and replacement. It is called Avacopan and is licensed for severe cases. In overwhelming inflammation, large doses of steroids and an exchange of blood water (=plasma) might be added for a short while to accompany the other treatments to speed up achieving control of active vasculitis.

When the disease is under control, patients remain on less intense medication to suppress the immune system (=immunosuppression) for a while to avoid vasculitis recurring. The standard maintenance drugs are rituximab and azathioprine but it might be that other drugs such as methotrexate and mycophenolate mofetil are used. The physician will try to withdraw steroids and later the maintenance treatment as well. Some people will relapse but not all. So, it is important to check whether the patient requires prolonged treatment to avoid overtreatment.

Drugs and Side effects

For information on the main drugs prescribed for Microscopic Polyangiitis see:

For information on other drugs used in the treatment of vasculitis see Glossary of drugs and side effects.

Treatment – Plasma exchange or plasmapheresis

The blood water, carrying blood cells, is called plasma. In active vasculitis, many inflammation and clotting molecules and the vasculitis antibodies, ANCA, are found in the patient’s blood. In severe cases of vasculitis, organ function and life are threatened and the healthcare professionals might decide to add plasma exchange to the other treatments. Antibodies and inflammatory components are removed from the blood using a machine. The treatment may necessitate giving blood products to the patient including plasma, albumin or immunoglobulin. It may also involve giving drugs to thin the blood.

For information on plasma exchange:

Prognosis

The prognosis in MPA depends on the disease severity and organ damage caused by the vasculitis. Relapses are less likely but MPA can slowly and undetected scar kidney and lung tissue for a while.

Key Points

  • MPA is a rare form of small vessel vasculitis
  • It often causes severe kidney and lung damage
  • Treatment often requires steroids in combination with cyclophosphamide or rituximab.

Related Vasculitis Articles

Further reading

Useful links

Our Useful Vasculitis Links page contains contact details for organisations offering help and support for patients with Microscopic Polyangiitis and other vasculitis diseases.