Polyarteritis Nodosa

Polyarteritis nodosa (PAN) is a rare form of systemic vasculitis that results in systemic necrotizing inflammation of the blood vessels. Vasculitides are a heterogeneous group of autoimmune diseases of the blood vessels and occur due to molecular mimicry, an autoimmune response in which the body’s immune system misidentifies normal antigens on the endothelial cells with the antigens of foreign invaders. Vasculitides can be grouped by vessel size (i.e., small, medium, large). PAN is a disease that primarily affects medium-sized blood vessels and multiple organ systems. It results in widespread systemic inflammation and long-term damage to the peripheral nerves.     

PAN is most commonly seen in middle-aged or older adults, with a peak incidence in the sixth decade of life, although children can also be affected. It is slightly more common in those assigned male at birth and is associated with hepatitis B infection. Arterial networks are widely distributed throughout the body, therefore, all organs may potentially be involved. Nonetheless, PAN classically affects the kidneys, gastrointestinal tract, central nervous system, and skin, while sparing the pulmonary system.     

Diagnosis of PAN begins with a thorough review of symptoms and medical history. A focused physical examination can help determine the extent of vascular lesions and determine if there is neurologic involvement. A positive fecal occult blood test may be indicative of gastrointestinal involvement. While there are no diagnostic blood tests for PAN, a basic laboratory panel may help characterize the extent of organ involvement. For example, serum creatinine and urinalysis can be useful in the assessment of renal function. Hepatitis B and C serologies should be obtained since chronic hepatitis infection is a risk factor for PAN. Due to the rarity of the disease and severe treatment-related adverse effects, confirmation with a biopsy of an arterial lesion is recommended whenever possible. In the absence of an available biopsy site, imaging with an angiogram or arteriogram (i.e., an imaging procedure that involves injection of a dye into the arteries to help visualize blood flow to organs) may reveal the classic “string of beads” appearance of blood vessels in the renal, hepatic, or mesenteric vasculature.  
 
Moreover, the American College of Rheumatology (ACR) has established ten criteria for the classification of PAN in an individual diagnosed with vasculitis. There is a high likelihood that an individual meets the criteria for PAN if they meet at least three of the following: 

(a) Unexplained weight loss greater than four kilograms 
(b) Presence of livedo reticularis  
(c) Testicular pain and/or tenderness 
(d) Muscle pain excluding the shoulder and hips, muscle weakness, tenderness of leg muscles 

(e) Presence of mononeuropathy or polyneuropathy 
(f) New onset diastolic blood pressure greater than 90 mmHg 
(g) Elevated BUN (>40 mg/dl) or SCr (>1.5 mg/dl) 
(h) Serologic evidence of hepatitis B virus infection 
(i) Presence of “string of beads” appearance on angiography 
(j) Confirmation via biopsy of blood vessel demonstrating polymorphonuclear cells 

Differential diagnoses that can present similarly (i.e., systemic sclerosis, systemic lupus erythematosus, drug-induced vasculitis) should be excluded via a thorough rheumatologic work-up and laboratory testing (e.g., antinuclear antibodies, anti-dsDNA, anti-RNP, scleroderma antibodies).