Pain caused by the nervous system itself is called neuropathic pain. It may be due to damage to the nerves, or other changes in the nervous system. Damage does not always cause pain - it may just cause numbness. The nerves could be damaged by injury, disease or surgery. Also chronic pain can cause sensitization of the nervous system, so that pressure may be felt as pain. This is the most difficult type of pain to treat.
Neuropathic pain is normally diagnosed on the basis of the patient's history of possible nerve damage, and the nature of the symptoms. If the pain feels abnormal - for instance, touching the skin causes pain - then the pain may be neuropathic.
Conventional painkillers, from aspirin to morphine, are not very effective at reducing neuropathic pain. Two drugs that have been found to help with neuropathic pain are ones that are normally used to treat depression (tri-cyclic anti-depressants) or epilepsy (anti-convulsants). For more details, see the drugs page.
TENS and spinal stimulation are also used to treat neuropathic pain.