Polyarteritis nodosa is one of the earliest forms of systemic vasculitis described. It is characterized by segmental necrotizing arterial lesions affecting medium-sized and small-sized arteries. Active necrotizing lesions are frequently associated with chronic reparative lesions. Current convention would exclude patients with necrotizing glomerular lesions from this category. An aneurysm may form when the arterial wall is sufficiently weakened by the necrotizing process. Any organ may be affected; however, pulmonary involvement is very uncommon. Significant potential exists for end organ injury resulting from ischemia, infarcts, and hemorrhage. A variety of other primary systemic vasculitidies, secondary forms, such as connective tissue disease associated, and organ limited forms, have been identified that may exhibit similar arterial lesions including aneurysm formation. Establishing a definitive diagnosis of polyarteritis nodosa is therefore challenging, and mandates dialogue between the pathologist and the clinician primed with pertinent clinical and laboratory data. Fortunately, with early diagnosis and aggressive treatment with cytotoxic agents, the prognosis of polyarteritis nodosa has substantially improved.
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