Description

• Polyarteritis nodosa (PAN) is an antineutrophil cytoplasmic antibody (ANCA)-negative necrotizing arteritis of medium-sized muscular arteries and (occasionally) small arteries. Arterioles, capillaries, and venules are spared (1).
• Involved systems include gastrointestinal (GI) tract, peripheral nervous system (sensory and motor), CNS, genitourinary, skin, and cardiovascular. Glomerulonephritis and pulmonary capillaritis are rare (1),(2).
• Features depend on location of vasculitis: for example, mesenteric ischemia–related symptoms, new onset or worsening hypertension (HTN), mononeuritis multiplex, purpuric or nodular skin lesions, or livedo reticularis (2).
• Renal disease in PAN usually manifests as HTN and mild proteinuria with/without azotemia (2).
• PAN formerly encompassed several distinct entities (classic PAN, microscopic PAN, and cutaneous PAN). With ANCA testing, microscopic PAN appears pathophysiologically unrelated to the other two.
  • Idiopathic generalized PAN (classic PAN) is clinically variable, ranging from single organ involvement to polyvisceral failure (1).
  • HBV-associated PAN patients are positive for active hepatitis B infection and can present in similar fashion to idiopathic generalized PAN (1).
  • Microscopic PAN has ANCAs directed against myeloperoxidase (MPO) and involvement of small arterioles (microscopic polyangiitis [MPA]). This is now classified as ANCA-associated vasculitis.
  • Cutaneous (or limited) PAN is generally limited to the deep dermal and subcutaneous (SC) levels of the skin with characteristic histopathologic features of PAN. There are few systemic manifestations, although myalgias and peripheral motor neuropathy (mononeuritis multiplex) or sensory neuropathy may be present (2).

Epidemiology

Incidence
Incidence of 0 to 1.6 cases per million; predominant age: peaks in 5th to 6th decade; incidence rises with age. Mean age at diagnosis is 50 years; male predominance

Prevalence
Rare: up to 31 cases per 1 million adults (1)

Etiology and Pathophysiology

• Segmental, transmural, necrotizing inflammation of medium and small muscular arteries, with intimal proliferation, thrombosis, and ischemia of the end-organ/tissue supplied by the affected vessels; aneurysm formation at vessel bifurcations (2)
• Hepatitis B–related PAN results in direct vessel injury due to viral replication or deposition of immune complexes, with complement activation and subsequent inflammatory response (2).
• Most cases are idiopathic; 20% are related to hepatitis B or C infection.
• In patients with PAN and hepatitis B, HBsAg has been recovered from involved vessel walls.

Genetics
Mutations of adenosine deaminase 2 (ADA 2) have been identified in families with PAN (1).

Risk Factors

Hepatitis B > hepatitis C infection (cutaneous PAN)

Commonly Associated Conditions

• Hepatitis B (strong association with classic PAN); hepatitis C (less strongly linked to cutaneous PAN)
• Hairy cell leukemia; rare following hepatitis B vaccination
• Minocycline (symptoms resolve on stopping drug, reoccur if rechallenged); case-based associations with CMV infection, amphetamines, and interferon