The Nervous system’s sensory nerves transmit signals from throughout the periphery to the brain, where the signal is processed. Injury or disruption of the nerve fiber may result in inappropriate activation of the nerves.
Neuropathic pain can be a chronic and debilitating condition. Symptoms include changes in sensation, including burning pain and tingling or numbness. Some people describe their pain as “pins and needles.” These sensations are known as dysesthesia. Pain produced by stimuli that would not normally cause pain is known as allodynia.
Common causes of nerve damage and subsequent neuropathic pain include diabetic neuropathy, trigeminal neuralgia (facial nerve pain), effects of cancer treatment including chemotherapy and radiation. Furthermore, shingles, a nerve condition in which the herpes zoster virus lives dormant in the nerve endings can cause severe pain that persists to post-herpetic neuralgia. Pain from nerve impingement or entrapment can include disc herniation, carpal tunnel syndrome, and spinal stenosis.
The central nerves system includes the brain and spinal cord. Central neuropathic pain is caused by injuries to these nerve centers. An example is multiple sclerosis. The nerves that send sensory signals from the rest of the body to the spinal cord and then to the brain make up the peripheral nervous system. Diabetic neuropathy is probably the most common cause of peripheral neuropathic pain, but other causes include the effects of vitamin deficiencies, toxins (chemotherapies) or impingement syndromes.
Treatment of neuropathic pain is very difficult in many cases. In case of toxins, vitamin deficiency, or diabetes, management of the precipitating condition will sometimes ameliorate the symptoms somewhat. Taking into consideration the medications that are generally used as anti-depressants and anti-epileptics which are used to treat neuropathic pain, they primarily work because of their interaction with specific ion channels in neurons that regulate transmission of neural impulses.
Topical preparations include anesthetics like lidocaine, or topical anti-inflammatory agents. Capsaicin induces pain and depletes substance P, and has modest effects when used for neuropathic pain. Botox injections are helpful in the treatment of small areas of focal neuropathic pain. NMDA antagonists include ketamine and dextromethorphan, and have some utility, with weak activity or unacceptable side effects.
Finally, for refractory neuropathic pain, neuromodulation has been effective treatment.