A 48-year-old man presented with a 2-week history of left-foot drop and diffuse muscle pain. He also reported 3 months of progressive, postprandial abdominal pain, fever, and 15-lb weight loss. His past medical history was notable only for mild hypertension, and his only medication was amlodipine. Physical examination was remarkable for hypertension (175/85 mm Hg), fever (39.8°C), livedo reticularis on his thighs, tenderness with palpation of quadricep muscles, and tenderness with palpation of abdomen without audible bruits, guarding, rebound, or palpable masses. Neurologic examination confirmed a left-foot drop.

Complete blood count (CBC) displayed leukocytosis (white blood cell count 15,500/mm³), normocytic anemia (hematocrit 30%), and thrombocytosis (platelet count 670,000/mm³). Blood urea nitrogen (BUN) (44 mg/dL), serum creatinine (2.1 mg/dL), and urinalysis showed only trace proteinuria. Creatine kinase was elevated at 650 U/L. Erythrocyte sedimentation rate (ESR) (87 mm/h) and C-reactive protein (CRP) (46 mg/L) were also elevated.

A mesenteric arteriogram revealed several areas of aneurysmal dilation in the mesenteric arteries. A biopsy of the left sural nerve identified transmural arterial inflammation with infiltration of polymorphonuclear lymphocytes. Subsequently, a diagnosis of polyarteritis nodosa was made. Testing for hepatitis B infection was negative. He was treated with high-dose oral glucocorticoids and oral cyclophosphamide and gradually improved.

Polyarteritis nodosa (PAN) is a rare disease that can present at any age and has no racial or ethnic predilection. PAN affects males slightly more frequently than females (1:1.17 male-to-female ratio). The incidence of PAN is higher in populations with a high burden of hepatitis B virus infection, and the frequency of hepatitis B–related PAN has decreased with the increasing availability of the hepatitis B vaccination.^1,2

PAN is a vasculitis primarily of medium-sized arteries, particularly in the kidney, gastrointestinal tract, peripheral nervous system, skin, and central nervous system. Other potential targets of the disease include joints, muscles, liver, spleen, heart, gonads, and eyes. PAN may involve nearly any medium-sized artery, although the pulmonary arteries are usually spared.^1,3,4

In PAN, biopsies of affected arteries show patchy, transmural inflammation sparing capillaries, larger arteries, and the venous system. Fibrinoid necrosis and pleomorphic cellular infiltrate without granulomatous inflammation are characteristically seen in the affected vessel walls. Aneurysmal dilation and stenosis occur as a result of disruption of the vessel walls’ elastic laminae.^1,2,4

PAN is challenging to diagnose as patients often present with nonspecific symptoms including fever, malaise, arthralgias, and weight loss. Postprandial abdominal pain is often present when the mesenteric arteries are involved. Gonadal involvement may mimic testicular or ovarian torsion. Physical examination may reveal hypertension, livedo reticularis (Figure 81-1), purpuric skin lesions (Figures 81-2 and 81-3), digital ulcerations, skin ulcers (Figure 81-3), arthritis, myositis, or signs of neuropathy (typically mononeuritis multiplex). The pulmonary vasculature is typically spared.^{1,2,4,5, and 6}

The laboratory findings in PAN are nonspecific, nondiagnostic, and may include leukocytosis, anemia, and elevated inflammatory markers (ESR or CRP). Urinalysis is typically bland as the pathology is arterial insufficiency rather than glomerulonephritis. Autoantibody tests are not useful except to exclude other disorders. Testing for hepatitis B infection should always be performed when PAN is suspected.^1,4

The diagnosis of PAN hinges on demonstration of characteristic histologic changes on biopsy (discussed earlier) or radiographic findings in affected arteries. Angiography reveals dilation and stenosis of affected arteries as a result of fibrinoid necrosis, leading to the classic “beads on a string” appearance often seen on mesenteric or renal angiography (Figure 81-4). While computed tomography (CT) and magnetic resonance imaging (MRI) angiography are less invasive and can be diagnostic, these modalities lack sensitivity in detecting smaller vessel involvement. As a result, conventional angiography remains the imaging gold standard in suspected PAN.¹ The PAN classification criteria developed by the American College of Rheumatology (ACR) are highlighted in Table 81-1.⁷