There are two primary types of pain - nociceptive (somatic) pain and neuropathic pain. Both of these pain categories involve the firing of nerve fibers that trigger the experience of pain, but the true source of the pain signals are very different. With nociceptive, or somatic pain, there is a true physical source/reason for the pain signal, such as an injury to the bones, muscles, muscle fascia, tendons or ligaments. With somatic pain, the impairment or injury to one of these physical structures causes changes in the surrounding tissues in the form of heat, swelling, and chemicals that trigger an inflammatory response. The sensory receptors in the form of nerve endings - nociceptors - recognize the changes and initiate a pain response. In a typical case of an injury that causes somatic pain, these nociceptors will continue firing these pain signals until the injury has healed itself.
While the firing rate of somatic pain signals tapers off and ceases as the original site of injury begins to heal itself, neuropathic pain signals may continue indefinitely - even after a healed injury or the absence of injury. Neuropathic pain is nerve pain. With this type of pain, the initiation of the firing of nerves that trigger the experience of pain may have originates with a specific location of injury, but continues even after that area of the body has fully healed. This misfiring of the nerves may continue due to the fact that the nerves themselves become damage, because of neurologic or metabolic disease, or due to some other pathology affecting nerves throughout the body. The misfiring nerves that continue to fire, in the absence of tissue injury, may begin to affect the nearby nerves, causing them to also begin misfiring. Eventually, your brain becomes triggered to feel pain, in spite of an array diagnostic tests that fail to find the cause of your pain.
These nerves may begin to malfunction, sending inappropriate pain responses to the brain, for a number of reasons. Neuropathic pain may be caused by a previous injury, shingles, multiple sclerosis, HIV infection, diabetes, chemotherapy, amputation, or surgery, particularly spinal surgery. The symptoms of this type of pain include numbness, burning, or tingling. This type of pain is typically the cause of phantom limb, a condition where patients with amputated limbs continue to experience the sensation of pain in limbs that are not longer there. Though analgesics such as nonsteroidal anti-inflammatory medications may provide some relief for patients with neuropathic pain, they do not treat the source of the pain, which are the nerves themselves.
Medications that inhibit the pain response, which is our perception of pain, may provide some relief from neuropathic pain. Some of these types of medications include Opiods (hydrocodone, Oxycodone, Methadone), topical agents (Lidocaine), and Cannabinoids (Marajuana). Other medications target nerves in the peripheral nervous system from allowing their signals from reaching the spinal cord and traveling up to the brain. These nerve-inhibiting medications include antidepressants such as nortriptyline, venlafaxine, and duloxetine and anticonvulsants such as oxcarbazepine (Trileptal) and carbamazepine (Tegretol). Benfotiamine and alpha lipoic acid are two dietary supplements that have shown some success in treating in treating neuropathic pain associated with Diabetes.