Ir is pain that has its origin in malfunction ot nerve system, either peropheric o central. That cause might be an inflammation of peripheral nerves o spinal roots as well as failure of pain regulation in teh CNS - e.g. fibromyalgia. Other common cause are metabolic diseases like DM causing diabetic neuropathy and angiopathy. Generaly said, the nerve pain is that one where there is no o minimal damage in the tissue except the nerve system.