Although doctors know something about the situations in which phantom pain occurs, they don't know exactly the cause of the pain. Researchers have suggested several theories.

Many doctors once thought that phantom pain was a psychological rather than a physical problem. They believed that pain resulted from a person's unwillingness or inability to accept the loss of a limb, or from a person's being overly concerned about the loss. Later research found that psychological distress is not the sole cause of phantom pain and may not be involved at all.

Causes of phantom pain may include:

• Pre-amputation pain. Some researchers have found that people who had pain in a limb before amputation are likely to experience phantom pain afterward. This connection may be strongest in the period of time immediately after amputation.

• Blood clot in the amputated limb. People who had surgery because of a blood clot in the amputated limb report phantom pain and discomfort both before and after rehabilitation more often than do people who had amputations for other reasons. Researchers think this may occur because the clot reduces the amount of oxygen available to the limb, damaging it. Remaining tissue that was damaged may take longer to heal than healthy tissue or may never heal, resulting in prolonged pain.

• Other factors. Pain that occurred intermittently but was not present immediately before an amputation may influence whether phantom pain develops. Pain related to gangrene or other infections prior to the amputation also may be more likely to result in phantom pain after surgery. Certain injuries such as nerve roots being torn away from your spinal cord (root avulsion) and damage to your nerve networks (plexus) also increase your risk of phantom pain.

Brain adjustments
As researchers learned more about how the brain can "rewire" itself after trauma such as surgery, some theorized that people experience phantom limb sensation in an upper limb when a different part of the body, such as the face, is stimulated. One research team found that the amount of brain rewiring is directly proportional to the degree of phantom limb pain. They found more rewiring in people with phantom pain symptoms than in people without symptoms.

There's no medical test to diagnose phantom pain. Among the information that doctors use to diagnose phantom pain are the signs and symptoms and the circumstances (such as trauma or surgery) that occurred before the pain started.