Characteristics of phantom pain include:

• Onset within the first week after amputation, though it can be delayed by months or longer
• Pain that comes and goes or is continuous
• Symptoms affecting the part of the limb farthest from the body, such as the foot of an amputated leg
• Pain that may be described as shooting, stabbing, cramping, pins and needles, crushing, throbbing, or burning

The exact cause of phantom pain is unclear, but it appears to come from the spinal cord and brain. During imaging scans — such as magnetic resonance imaging (MRI) or positron emission tomography (PET) — portions of the brain that had been neurologically connected to the nerves of the amputated limb show activity when the person feels phantom pain.

Many experts believe phantom pain may be at least partially explained as a response to mixed signals from the brain. After an amputation, areas of the spinal cord and brain lose input from the missing limb and adjust to this detachment in unpredictable ways. The result can trigger the body's most basic message that something is not right: pain.

Studies also show that after an amputation the brain may remap that part of the body's sensory circuitry to another part of the body. In other words, because the amputated area is no longer able to receive sensory information, the information is referred elsewhere — from a missing hand to a still-present cheek, for example.

So when the cheek is touched, it's as though the missing hand is also being touched. Because this is yet another version of tangled sensory wires, the result can be pain.

A number of other factors are believed to contribute to phantom pain, including damaged nerve endings, scar tissue at the site of the amputation and the physical memory of pre-amputation pain in the affected area.

Not everyone who has an amputation develops phantom pain. Some factors that may increase your risk of phantom pain include:

• Pain before amputation. Some researchers have found that people who had pain in a limb before amputation are likely to have it afterward. This may be because the brain holds on to the memory of the pain and keeps sending pain signals, even after the limb is removed.
• Residual limb pain. People who have persistent pain in the remaining part of the limb usually have phantom pain, too. Residual limb pain can be caused by an abnormal growth on damaged nerve endings (neuroma) that often results in painful nerve activity.