What Causes Neuropathic Pain?
Neuropathic pain occurs when either the central or peripheral somatosensory nervous system becomes damaged or diseased. The central nervous system consists of the brain and spinal cord, which can become damaged by spinal cord injuries, degenerative medical conditions such as multiple sclerosis, or, in some cases, strokes. The peripheral nervous system, which refers to any somatosensory nerves outside of the brain and spinal cord, is most commonly damaged by metabolic conditions like diabetes, but it can also be affected by certain infections, nutritional deficiencies, autoimmune conditions, or physical trauma. Neuropathic pain is also commonly associated with cancer, either because a tumor is compressing a nerve stem or because of nerve damage caused by aggressive chemotherapies.
What is Neuropathic Pain?
There are several mechanisms by which neuropathic pain can develop. In the peripheral nervous system, it usually takes the form of a nerve lesion that doesn’t heal correctly, leading to overly sensitive neurons. The aberrant increase in sensitivity causes the nerves to become much more easily activated in a phenomenon known as peripheral sensitization. Damage to the central nervous system works slightly differently. When triggered by damage or disease, neurons in the dorsal horn of the spinal cord cause a response in the anterolateral system, a sensory pathway between the skin and the thalamus. This feedback loop results in an ascending nociceptive (pain in response to harm) pathway. The increased nervous activity conditions the neurons in the anterolateral system to develop heightened background activity and increased sensitivity, ultimately leading to neuropathic pain. It is also possible for neuropathic pain within the peripheral system to stimulate secondary pain in the central nervous system in a similar way.
Neuropathic Pain Treatment
Neuropathic pain can be very difficult to treat, and for many patients, no one treatment will be able to fully eradicate the pain. However, a range of different therapies is available for neuropathic pain treatment, the most common of which are antidepressants, anticonvulsants, and topical numbing agents such as lidocaine. Antidepressants are generally considered to be the first-line medication for neuropathic pain, particularly serotonin-norepinephrine reuptake inhibitors. Anticonvulsants such as pregabalin have been found to be successful for patients with neuropathy linked to diabetes, while gabapentin is more commonly used for a specific form of neuropathy called fibromyalgia. Typically, anticonvulsants are tested for a short period with each patient, as they are known to have side effects and may not be an effective treatment for neuropathic pain. Other, more recent treatments have also started to become available. For example, the use of cannabis or other cannabinoid receptor agonists has been shown to be effective at treating neuropathic pain in some patients. Similarly, deep brain stimulation has shown promise in early studies for achieving long-term pain relief. These treatments are less heavily studied than older techniques as a result of their novelty and so are less commonly used, but they may become more front-line treatments in the future.