Vasculitic neuropathy can be classified as nerve large arteriole and microvasculitis on nerve biopsy. We investigated different histopathological findings between 2 groups.

Nerve vasculitis is a rare but devastating condition that can be systemic or nonsystemic (localized). It predominantly involves smaller vessels compared with other vasculitic processes in the body. The microvessels supplying nerves can be categorized as large arterioles (75–300 µm) or microvessels (<40 µm). Other features of nerve vasculitis beyond direct vascular inflammation include axonal (Wallerian) degeneration, asymmetric or multifocal fiber loss, injury neuroma, hemosiderin-laden macrophages, neovascularization, and perineurial thickening. Histopathologic differences between large-arteriole and microvasculitic patterns have not been previously described. We investigated these findings between the groups.

This is a retrospective, observational cohort study of patients evaluated and biopsied at a single center between 2001 to 2020.  We collected clinical and histopathological data from patients whose nerve biopsies were either diagnostic or highly suggestive of nerve vasculitis.

278 cases were identified; 125 cases of large arteriole vasculitis and 153 cases of microvasculitis. Nerve large arteriole vasculitis had higher rate of axonal degeneration (56.1%) than microvasculitis (29.6%)(p <0.0001) and lower empty nerve strands (36.5 vs 44.8, p = 0.01). Nerve large arteriole vasculitis also demonstrated higher neovascularization (56.8% vs 39.3%, p=0.005), higher luminal occlusion (36.0% vs 9.2%, p<0.0001), higher recanalization (32.0% vs 3.9%, p<0.0001), higher fibrinoid necrosis (60.8% vs 0.7%, p<0.0001), and higher hemosiderin-laden macrophages (84.0% vs 60.1%, p<0.0001). Nerve microvasculitis displayed more perineurial thickening (46.4% vs 22.4%), more injury neuroma (22.2% vs 4.8%, p=0.0002) than nerve large arteriole vasculitis.

On histopathological ground, nerve microvasculitis has higher empty nerve strands, perineural thickening, and injury neuroma signaling chronicity while nerve large arteriole vasculitis expresses more active axonal degeneration with higher rate of fibrinoid necrosis, and vessel wall changes.