When the clinical picture or EMG suggest a chronic polyneuropathy is due to inflammatory, immune-mediated, or vasculitic causes, a sural (sensory nerve) biopsy helps comfirm the diagnosis. Typically the sural nerve in the foot is biopsied which leaves permanent numbness along the lateral foot. Motor nerves are not biopsied since that would create a permanent motor deficit, but biopsy of an adjacent muscle may reveal pathological changes indicative of motor nerve denervation.