Polyarteritis Nodosa (PAN)

Polyarteritis nodosa is a rare autoimmune disease featuring spontaneous inflammation of the arteries (arteritis, a form of blood vessel inflammation or "vasculitis"). Autoimmune diseases are characterized by an overactive, misdirected immune system that attacks one's own body. Because arteries are involved, the disease can affect any organ of the body. The most common areas of involvement include the muscles, joints, intestines (bowels), nerves, kidneys, and skin. Poor function or pain in any of these organs can be a symptom. Poor blood supply to the bowels can cause abdominal pain, local bowel death, and bleeding. Fatigue, weight loss, and fever are common. Polyarteritis nodosa is often abbreviated PAN.

Polyarteritis nodosa is most common in middle-age people. Its cause is unknown, but it has been reported after hepatitis B infection. Polyarteritis is not felt to be an inherited condition.

Polyarteritis nodosa causes symptoms and signs that are a result of injury to the blood vessels. Therefore, the symptoms and signs depend on which vessels are affected and to what degree. This can lead to organ damage or injury. For example, if blood vessels supplying the nerves or muscles are affected, the nerves or muscles can be damaged. If the blood vessels to the kidneys are affected, kidney damage with blood in the urine can result. Symptoms and signs can include fatigue, weight loss, high blood pressure, muscle pain (myalgia), joint pain (arthralgia), testicular pain, livido reticularis, nerve damage, and abdominal pain.

The diagnosis is supported by tests that indicate inflammation including elevation of blood sedimentation rate and C-reactive protein. The white blood cell count and platelet count can be elevated, while the red blood count is decreased (anemia). Hepatitis B virus (testing for either antigen or antibody) can be found in 10%-20% of patients with polyarteritis nodosa. Urine testing can show protein and red blood cells in the urine. In patients with nerves affected, nerve conduction tests are abnormal.

The diagnosis of polyarteritis nodosa is confirmed by a biopsy of involved tissue that reveals the inflamed blood vessels (vasculitis). Examples of tissues that are sometimes biopsied include nerves, muscle, kidneys, and bowel. Vasculitis of the bowel and kidneys can often be detected with an angiogram (X-ray testing while contrast "dye" is infused into the blood vessels).

The American College of Rheumatology established criteria for the classification of polyarteritis nodosa in 1990. For classification purposes (to group patients together for medical studies), a patient is said to have polyarteritis nodosa if at least three of the following 10 criteria are present:

1. Weight loss greater than/equal to 4 kg
2. Livedo reticularis (a mottled purplish skin discoloration over the extremities or torso)
3. Testicular pain or tenderness (occasionally, a site biopsied for diagnosis)
4. Muscle pain, weakness, or leg tenderness
5. Nerve disease (either single or multiple)
6. Diastolic blood pressure greater than 90 mm Hg (high blood pressure)
7. Elevated kidney blood tests (BUN greater than 40 mg/dl or creatinine greater than 1.5 mg/dl)
8. Hepatitis B virus tests positive (for surface antigen or antibody)
9. Arteriogram (angiogram) showing the arteries that are dilated (aneurysms) or constricted by the blood vessel inflammation
10. Biopsy of tissue showing the arteritis (typically inflamed arteries)

Polyarteritis is a serious illness that can be fatal. Treatment is directed toward decreasing the inflammation of the arteries by suppressing the immune system. Medications used to treat polyarteritis nodosa include high-dose intravenous and oral cortisone medications such as prednisone, as well as immunosuppressive drugs such as cyclophosphamide (Cytoxan) or azathioprine (Imuran).

When hepatitis B is present in patients with polyarteritis, antiviral medications (such as vidarabine and interferon-alpha) are used as primary treatments. Treatments have included various combinations of antiviral medications, plasma exchange, and immunosuppressive drugs.

The outlook for patients with polyarteritis nodosa depends on the degree of damage to affected organs and the response to treatments. For those patients with underlying hepatitis B infection, eradication of the virus is essential for optimal outcome.

The only prevention for polyarteritis nodosa is to avoid the risk of hepatitis B.