Pathophysiology of vasculitis

Vasculitis represents a spectrum of disorders that are often divided on the basis of the predominant vessel size affected into large-, medium- and small-vessel vasculitides. This chapter will focus on the pathogenesis of the anti-neutrophil cytoplasmic antibody (ANCA)-associated medium- and small-vessel vasculitides (AAV), and large-vessel vasculitis, Takayasu arteritis, and giant cell arteritis. Underlying pathogenic mechanisms in vasculitis remain to be fully understood. In particular, the initiating event(s) are not known. A combination of infectious or other environmental triggers on a susceptible genetic background is currently favoured. In addition to the vessel size affected, the mechanisms of vascular injury vary. Moreover, extravascular granulomatosis may play an important role in disease manifestations. The innate and adaptive immune systems contribute to its pathogenesis. Although pathogenic antibodies have not been identified in large-vessel vasculitis, ANCA are directly implicated in small- and medium-vessel AAV. Disease manifestations are varied and diverse and may include arterial stenosis or aneurysms, glomerulonephritis and renal failure, gastro-intestinal, pulmonary, cutaneous, and neurological complications, visual disturbance, deafness, and nasal bridge collapse. Life-threatening cardiovascular disease is also seen, with myocarditis, pericarditis, valvular heart disease, thrombosis, systemic and pulmonary arterial hypertension, and accelerated coronary heart disease all reported. Despite this, the prognosis for patients with vasculitis has improved significantly in recent decades. Further understanding of the pathogenesis of vasculitis will lead to the discovery of further therapeutic targets and novel, safer biologic therapies.