Vasculitis—inflammation of the vessel wall with vascular damage or attendant tissue injury— may be a manifestation of diverse diseases. Recent studies of classification, epidemiology, and pathogenic mechanisms of individual vasculitides provide a foundation for better understanding the broad array of clinical features encountered in patients. Intense scrutiny of the cellular components and mediators of vascular inflammation in several diseases has yielded details of spatial and temporal distribution of inflammatory molecules, some of which are the subject of new therapies. Many clinical questions remain unresolved. How we define and diagnose vasculitis continues to be debated among clinicians and pathologists. Given the pleomorphic expression of disease, what clinical features are central to a diagnosis? How do genetically determined responses of the host, duration of disease, and type of involved tissue influence the histological features? How do we target therapies at inflammation without interfering with healing?

Neuropathies are a prominent feature of the systemic and secondary vasculitides. The reasons for this frequency are not immediately clear. The microvasculature of the peripheral nerve is comprised of two functionally distinct systems, an extrinsic and an intrinsic system linked by a complex anastomotic network. The rich blood supply and the capacity of nerves to function reasonably well with anaerobic metabolism normally render the nerve relatively resistant to ischaemia. However, other anatomical and physiological characteristics such as watershed areas between the distribution of major nutrient arteries and lack of autoregulation of peripheral nerve blood flow provide an explanation of the vulnerability of nerve fibres to ischaemia with certain types of vascular injury.1 2 The immediate cause of the vasculitic neuropathies is inflammation and occlusion of the vasa nervorum resulting in ischaemia of the peripheral nerve. This widespread occlusion of epineurial, or rarely perineurial and endoneurial, arterioles causes multifocal central fascicular or sector degeneration of nerve fibres. …