involving smaller vessels often can be visualized only by use of conventional angiography The reference standard for diagnosing vasculitis remains histopathologic demonstration of vascular inflammation, although tissue specimens may not be available in many cases because of the inaccessibility of lesions or patchiness of the vascular involvement Management See sections below for PAN and KD POLYARTERITIS NODOSA Current Evidence The annual incidence of PAN in adults is approximately 0.3 per 100,000; no comparable data are available for children Corticosteroid therapy has reduced mortality from nearly 100% to approximately 20% PAN is characterized by focal, pan-mural, necrotizing inflammation of small- and medium-sized muscular arteries As the name implies, vessels affected by PAN typically develop nodules in the walls of muscular arteries Sites of bifurcation are particularly prone to involvement, presumably because of hemodynamic turbulence at these points Biopsies reveal a cellular infiltrate initially predominated by polymorphonuclear leukocytes and fibrinoid necrosis As lesions mature, mononuclear cells, thrombosis, and recanalization mark the healing process The etiology of PAN is unknown, although it is considered to be an archetype of immune complex–mediated vascular damage Most children with PAN have serologic evidence of an antecedent streptococcal infection; up to one-third of adults have chronic hepatitis B or C, with viral proteins demonstrable in the circulating and fixed immune complexes The incidence of hepatitis-associated PAN in children is significantly lower, particularly in Western countries Clinical Considerations Clinical Recognition Childhood PAN occurs in both cutaneous and generalized forms, and distinguishing between them may be difficult Both types display systemic manifestations, including fever, malaise, and myalgias However, generalized PAN is significantly more likely to also involve the renal, GI, and central nervous systems Common to both are rashes, although these are more likely to be nodular or lacy (so called livedo reticularis) in the cutaneous form, and urticarial, petechial, or ischemic in the systemic form Renal involvement (including proteinuria, abnormal urinary sediment, and hypertension), abdominal pain (often a manifestation of gut vasculitis), arthritis, mononeuritis multiplex, and CNS involvement (seizures, hemiparesis) typify generalized PAN Less commonly, children may have cardiac disease (pericarditis, cardiomegaly, EKG changes, myocardial infarction) or pulmonary involvement (diffuse infiltrates, pulmonary hemorrhage, or hemothorax) Clinical Assessment The patient should be examined carefully for signs of end-organ involvement, including blood pressure elevation, abdominal tenderness, arthritis, CNS disease (e.g., hemiparesis), cardiac disease (e.g., pericarditis, myocardial infarction), and pulmonary involvement Urinalysis is a useful marker for renal involvement Laboratory findings in polyarteritis are nonspecific but suggest both acute and chronic inflammation Most children have white blood cell counts higher than 15,000/mm3, hemoglobin