Page 170 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

146 Ezgi Deniz Batu and Seza Ozen

children from their adult counterparts with the most frequent ones being Henoch-Schönlein
purpura/IgA vasculitis (HSP/IgAV) and Kawasaki disease (KD) [3].

Their prevalence is quite high reaching 13.5 cases of HSP/IgAV per 100,000 [4], with
135 to 200 cases of KD per 100,000 in the Japanese population versus 9 to 17 cases of KD
per 100,000 in the Caucasian population [5]. With an estimated annual incidence of adult
HSP/IgAV of 0.8 to 1.8 cases per 100,000 [6] and 10 cases of adult granulomatosis with
polyangiitis (GPA) and MPA per million total population [7, 8] the estimated incidence of
childhood vasculitis of 50 cases per 100,000 children per year [3] represents a formidable
pediatric public health concern.

Many vasculitides affect both children and adults, however some like KD, occur
exclusively in childhood whereas pediatric giant cell arteritis (GCA) is rarely if ever
encountered. Children and adults also differ in the etiology, relative frequency of certain
stereotypical clinical manifestations, and prognostic characteristics of primary systemic
vasculitis [9, 10]. This may be due to immune system differences between adults and children
attributable in part to the aging process. The latter includes thymic involution which is
associated with a variety of immune features including, a decrease in the number of naive and
regulatory T-cells, continuous reshaping of the immune repertoire by persistent antigenic
challenges, reduced production of naive B-cells, and the dysregulation of toll-like receptors
which function in innate immunity [11]. These changes may also have direct linkage to
differing autoimmune disease susceptibilities. Adult classification criteria based on arbitrary
combinations of different disease characteristics with the purpose of differentiating closely
related syndromes [12] is not necessarily applicable to childhood vasculitides [12]. Whereas
the primary objective of classification criteria is to define homogenous patient populations for
clinical investigation [13], its use in complex diseases may be limited [14], and surely so in
clinical practice due to their low sensitivity [15].

In 1990, the American College of Rheumatology (ACR) proposed classification criteria
for adult vasculitides [16-21], however, there were a number of shortcomings, for example,
the exclusion of MPA and KD, and no reference to antineutrophil cytoplasmic antibodies
(ANCA)-associated vasculitides (AAV) [16-21]. Furthermore, these criteria were not
validated in children. In 2005, the Vasculitis Working Group of the Pediatric Rheumatology
European Society (PRES) proposed preliminary classification criteria for the commonest
childhood vasculitides including, HSP/IgAV, childhood polyarteritis nodosa (cPAN), cGPA,
childhood Takayasu arteritis (cTAK) and KD [22]. These criteria were validated and
approved in final form at the 2008 Ankara Consensus Conference [23, 24] with support from
the European League Against Rheumatism (EULAR) and the Pediatric Rheumatology
International Trials Organization (PRINTO).

Small Vessel Vasculitis

Immune Complex-Mediated

Henoch-Schönlein Purpura/IgA Vasculitis (HSP/IgAV)
HSP/IgAV is the commonest childhood vasculitis with an incidence of at least 135 per 1

million children [4]. It is estimated that 90% of HSP/IgAV patients are younger than 10 years

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