Types of Neuropathic Pain
Neuropathic pain is pain that serves no protective purpose but 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. The pain is often described as burning and may never resolve. Neuropathic pain is generally insensitive to nonsteroidal anti-inflammatory drugs (NSAIDs).
Postherpetic Neuralgia (PHN)
Postherpetic neuralgia, or PHN, is a chronic, burning painful condition that affects the nerve fibers. PHN may occur in almost any area, but is especially common on the torso. It develops in about 20% of patients after healing of herpes zoster rash (shingles). Following an initial infection, some of the virus can remain dormant in nerve cells. Years later, age, illness, stress, medications or other factors still not well understood can reactivate the virus. The rash and blisters associated with shingles usually heal within a month, but some people continue to experience pain for years thereafter. As the population ages, 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-Associated Neuropathy (HIV-DSP)
Painful HIV-DSP is characterized by significant pain in the hands and feet and 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. The autonomic nervous system, which controls heart rate, digestion, and breathing, may also be affected.
HIV-DSP is caused primarily by three factors: 1) direct activation of sensory neurons by the HIV virus, 2) the immune system’s fight against the infection, and 3) the drugs administered to treat HIV. Because of the painful HIV-DSP side effects, physicians and patients often find it difficult to maintain a full dose regimen of the drugs used to treat the virus.
Painful Diabetic Neuropathy (PDN)
PDN is caused by widely fluctuating and often excessive plasma glucose levels, which injure the sensory nervous system. The condition 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, PDN pain is typically first felt in the feet and hands.
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 due to 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 in which there may be painful swelling of the extremities and abnormal sweating.