Types of Neuropathic Pain
Neuropathic pain serves no protective purpose and persists following viral infection, trauma, certain medications, or metabolic insults. Nerves that remain intact following disease or injury are often hyperactive, signaling pain in the absence of painful stimuli. Neuropathic pain may never resolve and is often described as burning and generally insensitive to nonsteroidal anti-inflammatory drugs (NSAIDs).
Postherpetic Neuralgia (PHN)
Postherpetic neuralgia (PHN) is a chronic, burning, painful condition that affects the nerve fibers. It develops in about 20% of patients after healing of a herpes zoster rash (shingles). The rash and blisters associated with shingles usually heal within a month, but pain may persist. PHN may occur in almost any area, but is especially common on the torso. The estimated number of patients living with PHN varies widely and range form under 200,000 to 500,000. As the aging population increases, the incidence of PHN is expected to rise, since older people are more susceptible to shingles. In addition, people infected with HIV develop shingles up to 15 times more frequently than the general population.
Painful HIV-Distal Sensory Polyneuropathy (HIV-DSP)
Painful HIV-distal sensory polyneuropathy (HIV-DSP), 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 may also affect the autonomic nervous system, which controls heart rate, digestion, and breathing. The incidence of HIV-DSP is estimated to be less than one in 200,000 patients in the U.S.
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 caused by widely fluctuating and often excessive plasma glucose levels, which injure the sensory nervous system. PDN causes pain or loss of feeling in the toes, feet, legs, hands and arms. Pain is attributed both to the toxic effects of some glucose metabolites and damage to small (microvascular) blood vessels that supply the nerves. Like HIV-DSP, pain is typically felt in the feet and hands. 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. 60 to 70 percent of people with diabetes have mild to severe forms of nervous system damage, which may include PDN.
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. Cancer-related painful neuropathies may develop from neural invasion of the tumor or nerve damage following surgery, radiation, or chemotherapy. In addition, complex regional pain syndrome II (CRPS II) is a form of neuropathic pain which may involve painful swelling of the extremities and abnormal sweating.