Page 288 - The Vasculitides, Volume 1: General Considerations and Systemic Vasculitis

262 Elizabeth J. Brant, Julie G. McGregor, J. Charles Jennette et al.

chronic with potential for long-term and symptom-free remission, many challenges
remain to decrease diagnostic delays, increase our understanding of molecular
mechanisms of genetic and environmental risk factors for disease, and further refine and
personalize treatment strategies that maintain remission and minimize treatment-related
morbidity.

Keywords: ANCA, Vasculitis, Kidney

Introduction

Many forms of systemic vasculitis directly affect the kidneys, and resultant injury can
lead to chronic kidney disease and even end-stage kidney disease. Vasculitides affecting
small- and medium-sized vessels are particularly likely to involve the kidneys. They include
polyarteritis nodosa (PAN), IgA vasculitis (IgAV, formerly Henoch-Schönlein purpura),
microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA, formerly Wegener
granulomatosis), eosinophilic granulomatosis with polyangiitis (EGPA, formerly Churg-
Strauss syndrome), and cryoglobulinemic vasculitis. The most common culprits of kidney
injury among this group are IgAV in children; and MPA, GPA, and EGPA in adults. MPA,
GPA, and EGPA affect predominantly small vessels, and are often, although not always,
associated with the presence of antineutrophil cytoplasmic autoantibodies (ANCA). Given
their predilection for kidney involvement, further discussion in this chapter will focus
primarily on these ANCA-associated vasculitides (AAV).

Epidemiology

Most data on the incidence and prevalence of AAV derive from studies in Caucasian
populations of European descent, although there are also emerging data from Asia and parts
of the Middle East. Disproportionate reporting in Caucasians may reflect case ascertainment
bias, availability of diagnostic resources, or high prevalence of competing diagnoses, for
example, tuberculosis in the case of granulomatous disease, rather than true difference.
However, data from multi-ethnic populations suggest that there are true differences in disease
incidence based on geographical location, ethnicity, or race, or a combination thereof. As an
example, a study of a multi-ethnic population in a Paris suburb, 28% of who were of non-
European ancestry, found that the overall prevalence of AAV, as well as PAN, in Europeans
was twice that observed in non-Europeans [1]. Similar ethnic differences are seen in New
Zealand, where Europeans appear to have a much higher annual incidence of AAV of 60.2
cases per million individuals than the indigenous Maori population with 34.2 cases per
million individuals [2]. The annual incidence in Pacific Peoples in New Zealand of 17.26
cases per million individuals was also lower than that of Europeans.

The average incidence of AAV in Japan appears to be similar to that in the United
Kingdom (UK), with 22.6 and 21.8 cases per million individuals annually, respectively, [3]
however, with notable differences. In Japan, the vast majority (83%) of patients has MPA and
is MPO-ANCA positive. Conversely, 66% of patients in the UK have GPA, and a similar
number are proteinase 3 (PR3)-ANCA positive. Interestingly, kidney involvement was noted

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