Types of Neuropathic Pain
Neuropathic pain has been defined as pain initiated or caused by a primary lesion or dysfunction in the nervous system. Neuropathic pain can occur following viral infection, trauma, certain medications, or metabolic insults and serves no protective purpose. Nerves that remain intact following disease or injury are often hyperactive, signaling pain in the absence of painful stimuli. Neuropathic pain may last for years and in some patients never resolve. It is often described as a burning pain and is generally insensitive to nonsteroidal anti-inflammatory drugs (NSAIDs).
Postherpetic Neuralgia (PHN)
Postherpetic neuralgia (PHN) is a chronic pain disorder that results from the reactivation of the varicella zoster virus (shingles). Definitions of PHN vary, ranging from persistent pain for one month after shingle rash crusting to as long as six months after shingle rash crusting. Of the estimated one million shingles patients per year in the United States, up to 20% are estimated to go on to develop PHN. PHN may last for months to many years, and occurs more frequently in elderly and immunosuppressed populations. Consequently, as the population ages and the number of patients with immune suppression increases (e.g. cancer, HIV), the incidence of PHN is expected to rise.
Painful HIV-Distal Sensory Polyneuropathy (HIV-DSP)
HIV-associated distal sensory polyneuropathy (HIV-DSP) is the most common neurological complication of HIV infection; approximately one third of patients with HIV/AIDS experience symptoms due to HIV-DSP. HIV-DSP is characterized by significant chronic pain in the hands and feet, can lead to loss of sensation in the arms and legs. Symptoms range from mild tingling to severe and excruciating pain in response to normal daily stimuli, such as putting on socks.
HIV-DSP is primarily caused by three factors: 1) direct activation of sensory neurons by the HIV virus, 2) the immune system's fight against HIV, and 3) antiretroviral drugs. Because of painful HIV-DSP side effects, physicians and patients may find it difficult to comply with or tolerate a full dose regimen of HIV drugs.
Painful Diabetic Neuropathy (PDN)
Painful Diabetic Neuropathy (PDN) is chronic pain that results from damage to sensory nerves due to multiple factors including the metabolic insult from high glucose levels and glucose metabolites as well as inadequate oxygenation related to diabetic microvascular damage. Distal symmetrical sensory polyneuropathy is the most common form of diabetic neuropathy. The symptoms include paraesthesias, hyperaesthesia, and sharp, stabbing, shooting and burning pains that commonly present in the feet and are often worse at night. According to the National Institute of Diabetes and Digestive Kidney Diseases (NIDDKD), NIH, 23.6 million people (7.8 percent of the population) in the U.S. have diabetes. Painful diabetic neuropathy has been reported in 10-20% of all people with diabetes and it is estimated that up to 45% of patients who have had diabetes for 25 years or more will at some time experience painful neuropathy.
Other Types of Neuropathic Pain
Many medical conditions are associated with neuropathic pain, including traumatic nerve injury, stroke, multiple sclerosis, syringomyelia, epilepsy, spinal cord injury and cancer.