Which tests the electrical activity and function of nerves and muscles. EMG may help clarify any subtle neuropathic clinical signs with regards to a more precise localization of the and helps distinguish a neuropathy from a radiculopathy or from a myopathy in confusing cases. 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.