MORPHOLOGYThevasculitisresemblesthatseeninpolyarteritisnodosa.Thereisadensetransmuralinflammatoryinfiltrate,althoughfibrinoidnecrosisusuallyislessprominentthaninpolyarteritisnodosa.Thevasculitistypicallysubsidesspontaneouslyorinresponsetotreatment,butaneurysmformationduetowalldamagemaysupervene.Aswithotherarteritides,healingmaybeaccompaniedbythedevelopmentofobstructiveintimalthickening.Pathologicchangesoutsidethecardiovascularsystemarerarelysignificant.
Kawasaki disease typically manifests with conjunctival and oral erythema and blistering, edema of the hands and feet, erythema of the palms and soles, a desquamative rash, and cervical lymph node enlargement (hence its other name, mucocutaneous lymph node syndrome). Approximately 20% of untreated patients develop cardiovascular sequelae, ranging from asymptomatic coronary arteritis, to coronary artery ectasia, to large coronary artery aneurysms (7 to 8 mm in diameter); the latter may be associated with rupture, thrombosis, myocardial infarction, and/or sudden death. Treatment consists of intravenous immunoglobulin infusions (which suppress inflammation through unclear mechanisms) and aspirin, which when given together markedly decrease the incidence of symptomatic coronary artery disease.
Microscopic polyangiitis is a necrotizing vasculitis that generally affects capillaries, as well as small arterioles and venules. It also is called hypersensitivity vasculitis or leukocytoclastic vasculitis. Unlike in PAN, all lesions of microscopic polyangiitis tend to be of the same age in any given patient. The skin, mucous membranes, lungs, brain, heart, gastrointestinal tract, kidneys, and muscle all can be involved; necrotizing glomerulonephritis (seen in 90% of patients) and pulmonary capillaritis are particularly common. Microscopic angiitis can be a feature of a number of immune disorders, such as Henoch-Schönlein purpura, essential mixed cryoglobulinemia, or the vasculitis associated with connective tissue disorders.
In some cases, antibody responses to antigens such as drugs (e.g., penicillin), microorganisms (e.g., streptococci), heterologous proteins, or tumor proteins have been implicated. These reactions can either lead to immune complex deposition or trigger secondary immune responses (e.g., the development of ANCAs) that are pathogenic. Indeed, most cases of microscopic polyangiitis are associated with MPO-ANCA. Recruitment and activation of neutrophils within affected vascular beds is probably responsible for the disease manifestations.
Depending on the vascular bed involved, major features include hemoptysis, hematuria, proteinuria, abdominal pain or bleeding, muscle pain or weakness, and palpable cutaneous purpura. With the exception of patients with widespread renal or CNS involvement, immunosuppression and removal of the offending agent induce durable remissions.
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Fig. 10.26 ANCA-associatedsmallvesselvasculitis.(A)Microscopicpolyangiitis(leukocytoclasticvasculitis)withfragmentedneutrophilsinthethickenedvesselwall.(BandC)Granulomatosiswithpolyangiitis.(B)Vasculitisofasmallarterywithadjacentgranulomatousinflammationincludinggiantcells(arrows). (C)Lungfromapatientwithgranulomatosiswithpolyangiitis,demonstratinglargenodularcavitatinglesions.(A, Courtesy of Scott Granter, MD, Brigham and Women’s Hospital, Boston, Massachusetts. C, Courtesy of Sidney Murphree, MD, Department of Pathology, University of Texas Southwestern Medical School, Dallas,Texas.)