Peripheral nerve vasculitis: Classification and disease associations

The vasculitides are diverse disorders defined by inflammation of vessel walls with reactive damage to the mural structures and ischemic injury. Necrotizing vasculitic lesions of peripheral nerve microvessels measuring 75 to 300 microns in diameter impacts involves small arteries, large arterioles, and variably smaller vessels in the majority of primary and secondary systemic vasculitis. Microvasculitis, characterized by transmural non-necrotizing inflammatory lesions affecting the smallest arterioles typically less than 40 microns, impacting smaller arterioles, endoneurial capillaries, and venules, is a related histopathological feature typifying several other primary and secondary disorders, including nonsystemic vasculitis neuropathy, and the interrelated disorders of diabetic and non-diabetic lumbosacral radiculoplexus neuropathy, diabetic cervical radiculoplexus neuropathy, and painless diabetic motor neuropathy. The resultant clinical features in each of the vasculitic entities depend on the size of the vessels involved, severity of the inflammatory process, location and cumulative extent of the lesions along the peripheral nerve. In light of these observations, we favor a simplified binary clinicopathological classification of vasculitic neuropathy based upon the size of the affected vessels, and the separation into the broad categories of nerve large arteriole vasculitis and microvasculitis, which is meaningful in prognosis and the approach to treatment. This chapter reviews the essential aspects of the nosology and classification, clinicopathologic aspects, prognosis and selected management of the representative vasculitides.