--refers to a particular type of stubborn neural pain that results from damage to the spinothalamic tracts in the brain, which run from the thalamus, a central relay for sensory information, down the spine and upwards into the cortices. Damage there tends to compromise the ability of the body to switch pain signals on or off so that one has severe allodynia (pain perceptin wothout noxious stimulus causing it) along with pain perception way out of proportion to central stimulus.

It is common among post stroke patients if that stroke involves the spinothalamic tracts, and is also the source of a lot of pain in people with sensory multiple sclerosis who have lesions in the area (Montel Williiams is a well-known sufferer) and can also result from meningitis, B12 deficiency, and a host of other conditions.

See:

www.centralpain.org

It's certainly not easy to treat--many of the strategies are the same as others used for neuropathic pain. I've known central pain people who are on much higher doses of anti-epileptics than most doctors would feel comfortable with (such as 900mg Lyrica, or 4800mg Neurontin) in order to get some decent relief.