Polyarteritis nodosa (PAN) is a systemic vasculitis of small-or medium-sized muscular arteries; it typically involves the renal and visceral vessels and spares the pulmonary circulation. There is no association with ANCAs, but one third of patients have chronic hepatitis B infection, which leads to the formation of immune complexes containing hepatitis B antigens that deposit in affected vessels. The cause is unknown in the remaining cases.
MORPHOLOGYClassicPANisasegmental transmural necrotizing inflammation ofsmall-tomedium-sizedarteries,oftenwithsuperimposedthrombosis.Kidney,heart,liver,andgastrointestinaltractvesselsareaffectedindescendingorderoffrequency.Lesionsusuallyinvolveonlypartofthevesselcircumferenceandhaveapredilectionforbranchpoints.Impaired perfusion mayleadtoulcerations,infarcts,ischemicatrophy,orhemorrhagesinthedistributionofaffectedvessels.Theinflammatoryprocessalsoweakens the arterial wall, leadingtoaneurysmsandrupture.
Intheacutephase,thereistransmuralmixedinflammatoryinfiltratecomposedofneutrophilsandmononuclearcells,frequentlyaccompaniedbyfibrinoid necrosis andluminalthrombosis(
Fig.10.25 ).Olderlesionsshowfibrousthickeningofthevesselwallextendingintotheadventitia.Characteristically,allstagesofactivity(fromearlytolate)coexistindifferentvesselsorevenwithinthesamevessel,suggestingongoingandrecurrentpathogenicinsults.
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Fig. 10.25 Polyarteritisnodosa,associatedwithsegmentalfibrinoidnecrosisandthromboticocclusionofasmallartery.Notethatpartofthevessel(upper-right, arrow) isuninvolved.(Courtesy of Sidney Murphree, MD, Department of Pathology,University of Texas Southwestern Medical School,Dallas,Texas.)
PAN is primarily a disease of young adults but can occur in all age groups. The clinical course typically is episodic, with long symptom-free intervals. The systemic findings—malaise, fever, and weight loss—are nonspecific, and the vascular involvement is widely scattered, so that the clinical manifestations can be varied and puzzling. A “classic” presentation involves involve some combination of rapidly accelerating hypertension due to renal artery involvement; abdominal pain and bloody stools caused by gastrointestinal lesions; diffuse muscular aches and pains; and peripheral neuritis, predominantly affecting motor nerves. Renal involvement often is prominent and is a major cause of death. Untreated, PAN typically is fatal; however, with immunosuppression, 5-year survival is close to 80%. Relapse occurs in up to 25% of the cases, more often in non–HBV-associated cases than those that follow HBV infection. The latter have a better long-term prognosis.
Kawasaki disease is an acute, febrile, usually self-limited illness of infancy and childhood associated with an arteritis of mainly largeto medium-sized vessels. Approximately 80% of patients are younger than 4 years of age. Its clinical significance stems from the involvement of coronary arteries. Coronary arteritis can result in aneurysms that rupture or thrombose, causing myocardial infarction. Originally described in Japan, the disease is now recognized in the United States and elsewhere.
In genetically susceptible individuals, a variety of infectious agents (mostly viral) have been posited to trigger the disease. The vasculitis may result from a delayed-type hypersensitivity response directed against cross-reactive or newly uncovered vascular antigen(s). Subsequent cytokine production and polyclonal B cell activation result in auto-antibodies to ECs and SMCs that precipitate the vasculitis.