Are there features of a nerve biopsy that help distinguish late nerve damage from vasculitis versus from a demyelinating disease?  

Chronic demyelinating processes can have features of demyelination on nerve biopsy including thinly myelinated fibers, remyelinating fibers, onion bulb formation, myelinated fiber loss, and axonal regeneration, as well as variable degree of inflammation. Late vasculitic neuropathy would show axonal ...