Neuropathic pain is a malfunction in the somatosensory system that arises from a number of disease and idiopathic origins. It is not relieved by traditional painkillers as it is nociceptive pain produced by damage to tissues. There are several kinds of neuropathic pain, including dysethesia, allodynia, primary and secondary hyperalgesia and chronic paresthesia.
Neuropathic Pain Prevalence
Datamonitor states "The prevalence of neuropathic pain is estimated at approximately 10% in the adult population of the US, and is likely to be the same in other developed countries. Peripheral neuropathic pain is a common co-morbidity in HIV, diabetes and herpes zoster; it affects approximately 22% of HIV-positive individuals, 6% of type 1 diabetics, 18% of type 2 diabetics, and 6-18% of herpes zoster cases."(1)
Abnormal Pain Responses
Conditions such as multiple sclerosis, diabetes, Lyme disease and spinal cord injury cause lesions in the nervous system can lead to dysethesia. Allodynia is a pain response from a stimulus that normally would not induce pain such as light physical touch or stroking, heat or cold, or the normal movement of muscles and joints. Produced by damage to the peripheral nerves, both primary and secondary hyperalgesia present as pain sensitivity in and surrounding injured tissues. Chronic paresthesia is the least painful of these neurological disorders and is experienced as a tingling, burning or "pins and needles" sensation because of underlying traumatic nerve damage or neurological disease.
Treatment
Traditional painkillers lack efficacy in treating neuropathic pain. While treatment of underlying causes such as better management of diabetes can limit further nerve damage, it does not relieve the condition itself. Using tricyclic antidepressants has produced good outcomes; however, most tricyclic antidepressants have unpleasant and potentially debilitating side effects such as drowsiness, dry mouth, constipation, tremor, irregular heartbeat, and disorientation or confusion.(2) Other medications often prescribed to alleviate neuropathic pain include anticonvulsant medications such as gabapentin and pregabalin which are thought to interfere with the body's pain channels and thus reduce pain signals reaching the brain.(3)
Duloxetine as Treatment for Neuropathic Pain
Duloxetine is a serotonin and norepinephrine reuptake inhibitor and works to modify the neurotransmitters that pass the pain signal through nerves to the brain. Serotonin works to suppress pain and norepinephrine is the chemical released by the body as a response to stress that constricts blood vessels and raises blood pressure. It is believed that medications such as Duloxetine block the action of these neurotransmitters and thus interfere with the pain channels' ability to send signals to the brain. Studies have shown a high efficacy of Duloxetine in the treatment of chronic pain with few risks. Indeed, a review of research conducted by the Chronic Pain and Fatigue Research Center at the University of Michigan found that "the benefit/risk balance for duloxetine remains favorable in the chronic pain population."(4)
Neuropathic pain can be a debilitating condition that severely impacts quality of life. There are few treatments that completely resolve this neurological condition, although SNRIs such as Duloxetine have shown clinical efficacy in managing neuropathic pain from a variety of causes.
Sources
(1)http://www.reuters.com/article/2012/01/24/idUS188423+24-Jan-2012+BW20120124, retrieved 4/30/2014.
(2)http://www.mayoclinic.org/diseases-conditions/depression/in-depth/antidepressants/art-20046983, retrieved 4/30/2014.
(3)http://www.webmd.com/sleep-disorders/anticonvulsants-for-chronic-pain, retrieved 4/30/2014.
(4)http://www.fda.gov/downloads/AdvisoryCommittees/CommitteesMeetingMaterials/Drugs/AnestheticAndLifeSupportDrugsAdvisoryCommittee/UCM225311.pdf, retrieved 4/30/2014.
