10/11/2026
🩸 EPISODE 45: MICROSCOPIC POLYANGIITIS
Small-vessel inflammation that can damage vital organs
Microscopic polyangiitis—commonly shortened to MPA—is a rare form of ANCA-associated vasculitis.
MPA causes inflammation and injury primarily in small blood vessels. The kidneys and lungs are commonly affected, but the disease may also involve the skin, peripheral nerves, muscles, joints and gastrointestinal tract.
Symptoms may develop gradually over several months or progress rapidly within days. Early evaluation is important because kidney or lung damage can become serious before the diagnosis is recognized. (vasculitisfoundation.org)
GENERAL SYMPTOMS MAY INCLUDE:
• Fatigue or weakness
• Fever
• Poor appetite
• Unintended weight loss
• Muscle or joint pain
• A general feeling of being unwell
KIDNEY INVOLVEMENT
MPA may cause rapidly progressive glomerulonephritis—inflammation and damage within the kidney’s filtering units.
Possible findings include:
• Blood in the urine
• Protein in the urine
• Dark, red or cola-colored urine
• Swelling of the feet or legs
• High blood pressure
• Rising creatinine or declining kidney function
Kidney inflammation may initially cause no noticeable symptoms. Urinalysis and kidney-function testing can detect abnormalities before a person realizes that the kidneys are being affected.
LUNG INVOLVEMENT
Inflammation of the small blood vessels surrounding the lung’s air sacs may cause pulmonary capillaritis or diffuse alveolar hemorrhage.
Possible symptoms include:
• Persistent cough
• Shortness of breath
• Chest discomfort
• Coughing up blood
• Low oxygen levels in severe cases
Coughing up blood or developing severe breathing difficulty requires emergency medical attention.
SKIN AND NERVE INVOLVEMENT
Small-vessel inflammation may produce raised purple-red spots called palpable purpura, often appearing on the lower legs.
Peripheral-nerve injury may cause:
• Burning or shooting pain
• Numbness or tingling
• Muscle weakness
• Foot drop or wrist drop
HOW IS MPA DIAGNOSED?
There is no single test that confirms every case of microscopic polyangiitis.
Evaluation may include:
• Medical history and physical examination
• Urinalysis for blood and protein
• Creatinine and other kidney-function tests
• Complete blood count
• ESR and CRP inflammatory markers
• MPO-ANCA and PR3-ANCA blood tests
• Chest X-ray or CT when lung involvement is suspected
• Biopsy of an affected kidney, lung, skin, nerve or muscle
MPA is most often associated with MPO-ANCA. The term p-ANCA describes a laboratory staining pattern and is not synonymous with MPA.
Some people with MPA are ANCA-negative, while positive ANCA results can occur in other diseases. ANCA testing may support the evaluation, but it does not establish the diagnosis by itself.
A kidney biopsy may show pauci-immune necrotizing and crescentic glomerulonephritis. “Pauci-immune” means that few or no immune deposits are visible in the damaged kidney tissue.
HOW IS MPA TREATED?
Treatment depends on the organs involved, the severity of the disease and the person’s individual medical circumstances.
Severe or organ-threatening MPA is generally treated with:
• Rituximab or cyclophosphamide to suppress the abnormal immune response
• Glucocorticoids to control inflammation rapidly
The ACR/Vasculitis Foundation guideline conditionally favors rituximab over cyclophosphamide for remission induction in severe GPA or MPA. The 2024 KDIGO guideline recommends glucocorticoids combined with either rituximab or cyclophosphamide, with the choice individualized according to kidney function, previous treatment, relapse history, fertility considerations and other clinical factors. (vasculitisfoundation.org, kdigo.org)
AVACOPAN
Avacopan is FDA-approved as an add-on treatment for adults with severe active GPA or MPA in combination with standard therapy.
The 2024 KDIGO guideline also allows avacopan to be considered as an alternative to glucocorticoids in selected patients—particularly when reducing glucocorticoid exposure is important. Avacopan does not replace rituximab or cyclophosphamide when remission-induction treatment with one of those medicines is required. (kdigo.org, fda.gov, accessdata.fda.gov)
AFTER REMISSION
Maintenance therapy is usually continued to reduce the risk of relapse. Depending on the patient, this may include rituximab or azathioprine, sometimes with low-dose glucocorticoids.
Plasma exchange is not automatically required for everyone with MPA. It may be considered in selected patients with advanced or rapidly worsening kidney failure, dialysis dependence or diffuse alveolar hemorrhage with low oxygen. It is added when ANCA-associated vasculitis overlaps with anti-GBM disease.
IMPORTANT ANCA WARNING
ANCA results must be interpreted with the entire clinical picture.
Persistent ANCA positivity or a rising ANCA level may contribute information about relapse risk, but treatment should not be started, stopped or increased based on ANCA levels alone. Symptoms, examination, urine and blood tests, imaging and biopsy findings must be considered together.
🚨 WHEN TO SEEK URGENT CARE
Call emergency services for:
• Coughing up blood
• Severe or sudden breathing difficulty
• Chest pain with breathing problems
• Confusion, fainting or signs of dangerously low oxygen
Seek prompt medical evaluation for:
• Dark or bloody urine
• A major decrease in urination
• Rapidly worsening swelling
• New foot drop, wrist drop or significant weakness
MPA is serious but treatable. Early recognition and appropriate treatment may help prevent permanent kidney, lung or nerve damage.
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Sources: KDIGO 2024 ANCA-Associated Vasculitis Guideline; American College of Rheumatology/Vasculitis Foundation Guideline; Vasculitis Foundation; U.S. Food and Drug Administration.
