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Polyarteritis Nodosa - Microscopic Polyarteritis

What Does "Polyarteritis" Mean?
Simply inflammation ("itis") of many ("poly") arteries.

Are There Different Types Of Polyarteritis?
Yes. There are two types. Microscopic Polyarteritis(abbreviated to MPA) and classical Polyarteritis Nodosa (abbreviated to PAN).

MPA is the most common type seen in Britain today.  PAN is very rare but is seen occasionally in association with infection by Hepatitis B virus.

What Are The Similarities And Differences Between MPA And PAN?
Both disorders can affect men and women, and are seen occasionally in children.

MPA tends to attack very small blood vessels (including tiny capillaries in the kidneys) while PAN tends to attack larger arteries, often causing blockages.

Blockages in larger blood vessels can prevent blood reaching whole organs or parts of organs.  Inflammation and blockages of arterioles and capillaries also prevents oxygen reaching important tissues.

 

Other Differences Between MPA and PAN
Anti-neutrophil cytoplasm antibodies (ANCA) are present in the blood in MPA, as they are in Wegener's Granulomatosis.  They are usually absent in PAN.  The ANCA blood test is a useful guide to doctors when they make a diagnosis of MPA or Wegener's.

Symptoms Associated With MPA
Sometimes MPA just affects the kidneys so an individual may only begin to feel unwell when the kidney function has deteriorated, allowing poisonous substances to build up in the blood stream.  Kidney failure can be detected by blood tests that show the kidneys are no longer getting rid of urea and creatinine.

Other patients with MPA have feelings of lethargy, aches and pains in joints or muscles, red eyes, skin rashes or may have lung involvement.  Lung involvement in MPA may cause shortness of breath and blood may be coughed up.  These features are similar to those experience by patients with Wegener's.

PAN is rarely seen.  It can cause high blood pressure, abdominal pains due to poor blood supply to the bowel, skin rashes and joint pains.

 

Making A Diagnosis
The ANCA blood test and a kidney biopsy test, when a small piece of kidney is taken to look at under a microscope, are very helpful tests for MPA.

An X-Ray of the blood vessels themselves (an angiogram) which is done by injecting a special dye, is helpful for PAN.

Treatment
In MPA, cortisone (prednisolone) and cyclophosphamide are usually used in the early stages.  If the disease is severe, large doses of cortisone (Methylprednisolone) or plasma exchange may be given, when the disease becomes quiet, azathioprine is sometimes used instead of Cyclophosphamide.

Similar drugs may be used for PAN.  In addition, if Hepatitis B virus is present, treatments may be used to try to get rid of the virus.

 

Does The Treatment Have Side Effects?
Yes. Cortisone and Cyclophosphamide reduce the inflammation present in MPA but they also reduce the body's ability to fight infection.  The white blood cell count has to be carefully monitored. 

Cortisone can also cause sugar diabetes, high blood pressure, thinning and bruising of the skin and weight gain.  Nowadays most doctors try to reduce the dose of prednisolone as quickly as possible to prevent side effects.

Cyclophosphamide can cause inflammation of the bladder and infertility if used over long periods of time.

Can MPA Relapse?
Yes.  Unfortunately about half of patients will relapse sometimes in the months or years following initial illness.  That is why most doctors continue to observe patients in the outpatient clinic so that early signs of active disease can be treated quickly.

Acknowledgements
Dr. Wai Tse
The University of Birmingham Medical School

Prof. Caroline Savage
Senior Lecturer(Nephrology)
The University of Birmingham Medical School

 

 

 

 

 

 

 
 
 
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