Objectives To validate the previously proposed classifi cation criteria for Henoch-Schönlein purpura (HSP), childhood polyarteritis nodosa (c-PAN), c-Wegener granulomatosis (c-WG) and c-Takayasu arteritis (c-TA). MethodsStep 1: retrospective/prospective webdata collection for children with HSP, c-PAN, c-WG and c-TA with age at diagnosis ≤18 years.Step 2: blinded classifi cation by consensus panel of a representative sample of 280 cases.Step 3: statistical (sensitivity, specifi city, area under the curve and κ-agreement) and nominal group technique consensus evaluations. Results 827 patients with HSP, 150 with c-PAN, 60 with c-WG, 87 with c-TA and 52 with c-other were compared with each other. A patient was classifi ed as HSP in the presence of purpura or petechiae (mandatory) with lower limb predominance plus one of four criteria: (1) abdominal pain; (2) histopathology (IgA); (3) arthritis or arthralgia; (4) renal involvement. Classifi cation of c-PAN required a systemic infl ammatory disease with evidence of necrotising vasculitis OR angiographic abnormalities of medium-/small-sized arteries (mandatory criterion) plus one of fi ve criteria: (1) skin involvement; (2) myalgia/ muscle tenderness; (3) hypertension; (4) peripheral neuropathy; (5) renal involvement. Classifi cation of c-WG required three of six criteria: (1) histopathological evidence of granulomatous infl ammation; (2) upper airway involvement; (3) laryngo-tracheo-bronchial involvement; (4) pulmonary involvement (x-ray/CT); (5) antineutrophilic cytoplasmic antibody positivity; (6) renal involvement. Classifi cation of c-TA required typical angiographic abnormalities of the aorta or its main branches and pulmonary arteries (mandatory criterion) plus one of fi ve criteria: (1) pulse defi cit or claudication; (2) blood pressure discrepancy in any limb; (3) bruits; (4) hypertension; (5) Paediatric Rheumatology European Society propose validated classifi cation criteria for HSP, c-PAN, c-WG and c-TA with high sensitivity/specifi city. INTRODUCTIONIn 1990 the American College of Rheumatology (ACR) proposed classifi cation criteria for patients with vasculitides 1-5 by analysing 807 adults patients with different form of vasculitis: 85 with Henoch-Schönlein purpura (HSP), 118 with polyarteritis nodosa (PAN), 85 with Wegener granulomatosis (WG), 63 with Takayasu arteritis (TA) and 456 with other vasculitides (Churg-Strauss, hypersensitivity, giant cell arteritis and other unspecifi ed forms). 6 Patients with each specifi c vasculitis were compared with all the remaining diseases grouped into a single control category.The ACR criteria for HSP (sensitivity 87.1%, specifi city 87.7%) require the presence of at least two of the following: (1) age ≤20 years at disease onset; (2) palpable purpura; (3) acute abdominal pain; (4) biopsy showing granulocytes in the walls of small arterioles/venules. 1 The ACR criteria for PAN (sensitivity 82.2%, specifi city 86.6%) require at least three of the 10 following criteria: (1) granulocyte or mixed leucocyte infi ...

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