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Microscopic polyangiitis

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Microscopic polyangiitis (MPA) is a rare and potentially serious long term vasculitis. Inflammation of the blood vessel walls may affect any organ but particularly the lungs, kidneys and nervous system.

High dose immunosupression can achieve quick control and provide a good outcome for most patients.

Key points

  • Inflammation of the blood vessel walls is commonly associated with tissue breakdown and organ damage
  • Skin, lungs, kidneys and nervous system are commonly affected
  • Early treatment is with steroids and cyclophosphamide to gain control before swapping to a weaning regime of steroids and methotrexate or azathioprine

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How is it diagnosed?

Suspicion occurs when there is a persistent fever, weight loss and malaise plus one or more of the following:

  • Lung involvement with a cough, difficulty breathing or blood in the sputum
  • Kidney involvement detected as high blood pressure or abnormal urine or blood tests
  • Non-specific features such as a purple-red raised rash, joint pain, areas of sensory loss or limb weakness and a painful red eye

Blood tests may include a positive test for ANCA. A biopsy (of lung, kidney or skin) may show a characteristic appearance.

Other helpful tests may include:

  • Chest x-ray
  • Electrical tests of the nervous system
  • MRI of an affected organ

Referral to an ophthalmologist (eye specialist) may be helpful

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How is it treated?

Treatment depends on the severity of inflammation. In general there are three phases:

  1. Stop the inflammation (induce remission) with high dose steroids and cyclophosphamide
  2. Prevent or reduce recurrences of inflammation with methotrexate, mycophenolate or azathioprine and a reducing regime of prednisolone (steroid)
  3. Treat relapses (similar to phase 1)

See our A-Z of medicines for information about specific drugs.

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What is the outcome?

Over 90% of patients improve and 75% achieve complete remission.

Up to one third may relapse within 2 years.

The long term outcome depends on the organs affected the persistence or severity of inflammation and the form and amount of drugs used.

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