At a Glance

Vasculitis is an inflammation of the blood vessel wall. The various systemic vasculitides are often categorized based on the size of the involved blood vessels, namely small-, medium-, and large-sized vessels. Polyarteritis nodosa (PAN) is referred to as medium-sized vessel vasculitis and is associated with necrotic inflammation medium-sized arteries. In addition, inflammation of the arterioles, venules, and capillaries is absent. Patients with PAN often present with a spectrum of systemic features, including fatigue, fever, myalgia, and arthralgia.

The most commonly affected specific organ system is the skin. A variety of dermatologic manifestations may be observed, including livedo reticularis, subcutaneous nodules, ulcers, palpable purpura, and possibly digital gangrene. The peripheral nerves are also often affected, and the presentation of mononeuritis multiplex is considered strongly indicative of PAN. In PAN, monomeuritis multiplex most often affects the tibial, ulnar, median, and radial nerves and is almost always associated with sensory abnormalities.

Patients may also complain of gastrointestinal (GI) issues, often as a discomfort that becomes most evident after eating. Development of PAN is associated with hepatitis B infection, although this is now seen in a much smaller percentage of PAN cases because of the widespread availability of hepatitis B vaccination.

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What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Unfortunately, there is no specific laboratory test that is diagnostic for polyarteritis nodosa. Because PAN is associated with systemic inflammation, assessment of inflammatory markers is useful in the initial evaluation. Patients will often have elevations in the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). Other general laboratory findings may include anemia and thrombocytosis. Testing for anti-neutrophil cytoplasmic antibodies (ANCAs) may be useful for ruling out the ANCA-associated vasculitides, particularly microscopic polyangiitis. Hepatitis B testing is also useful, not necessarily to diagnose PAN, but to help guide therapy (Table 1).

Table 1
Elevated erythrocyte sedimentation rate, C-reactive protein
generally >50 mm/hr Normal or elevated
Although not specific for PAN, an abnormal result indicates an acute phase response and a proinflammatory state. Although not specific for PAN, an abnormal result indicates an acute phase response and a proinflammatory state.

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications – OTC drugs or Herbals – that might affect the lab results?

The treatment for PAN is immunosuppression, generally with corticosteroids. For patients with more severe disease, cyclophosphamide may be added to the steroid therapy. In addition, for patients who are hepatitis B positive, anti-viral therapy may be initiated.

Unfortunately, patients who present with evidence of systemic inflammation may be started on an immunosuppressive regimen before a specific diagnosis is established. For these patients, laboratory testing for acute phase reactants may be noninformative, as the steroid or other immunosuppressive agent may result in decreased or possibly even normalized ESR and CRP. Extreme caution must be used when interpreting a normal ESR or CRP in a patient being treated with corticosteroids (prednisone) or cyclophosphamide.

What Lab Results Are Absolutely Confirmatory?

A biopsy can, generally, be used to confirm the diagnosis of PAN. A biopsy of the affected skin or nerve is most informative. The biopsy may show a visible aneurysm or a rupture. In addition, histology may show the presence of inflammatory cells within the vessel wall, along with fibrinoid necrosis and narrowing of the vessel lumen. There are no blood-based laboratory tests that can be used to confirm the diagnosis.