Examples are Mononeuropathies (involve a single nerve [eg, carpal tunnel syndrome, radiculopathy due to a herniated intervertebral disk]) Plexopathies (involve multiple nerves within a particular neural plexus; typically caused by trauma, inflammation, or nerve compression, as by a tumor) Polyneuropathies (involve multiple nerves, often throughout the body; typically caused by various metabolic disorders, paraproteinemias, toxic exposures [eg, alcohol, chemotherapy]), hereditary predisposition, or, rarely, immune mediated mechanisms—see tables Causes of Peripheral Nervous System Disorders) Mechanisms of neuropathic pain are complex and involve changes At the peripheral nociceptor and nerve level At the dorsal root ganglion In central nervous system (CNS) nociceptive pathways and terminal structures At the peripheral nerve and nociceptor level, injury results in inflammation and in activation and over-representation of cation channels, particularly sodium channels.