HISTORY AND BACKGROUND
Phantom limb pain was described as far back as 1871 - the sensation of a limb that was no longer present was thought back then to be due to a ghost, hallucination, disturbance of body image, etc. As time went on, studies into the origin of this pain led to many theories as to the cause of this problem (see additional discussion below), It is still unclear as to the exact etiology of the problem.

DESCRIPTION
Phantom limb sensation occurs in almost all amputees. In many patients, this sensation will fade with time - and there is no pain experienced. This is distinguished from the syndrome of phantom limb pain - a chronic pain occurring in some smaller subset of patients.

The actual incidence of this problem is unclear - with acute incidence estimated at about 60% and chronic incidence estimated between 10-45%. The problem may be somewhat underreported because of the strange nature of the symptoms - patients know that they have no limb to attribute the symptoms to. Therefore they may be reluctant to raise the issue - fearing that they will be thought of as crazy, etc. However, it is clear that this is a very common problem - and when it involved pain can be a even more difficult issue to deal with and treat.

SYMPTOMS
Interestingly, in patients that report this problem the "phantom limb" is often said to be in a contorted or abnormal position - one which would be painful if the actual limb were in that posture.distorted, grotesque or in an abnormal posture which in an intact limb would be painful. In addition, stretching of the limb or uncontrollable movements of the phantom limb are often reported.

Other symptoms of this syndrome include stabbing, squeezing, cramps, shooting, and burning of the phantom limb.

Many patients report that fatigue, anxiety, cold, and other changes in the weather pattern seem to make the condition worse.

THEORIES OF CAUSE
There are several theories as to the pathophysiology of phantom limb pain. These are not widely agreed upon and all have some supporting data. The theories are divided into peripheral causes (those that happen at the nerves around the injury), spinal causes (changes in the spinal cord causing the sensation) and central causes (those that are due to some mechanism in the brain).

Here are some examples of possible and popular theories:

1. peripheral cause - sensation due to a loss of previously present peripheral nerve activity
2. peripheral cause - regeneration of the nerves that were injured/cut
3. peripheral cause - neuroma formation with resulting painful nerve activity
4. peripheral cause - alteration in ion channel activity at the site of injury
5. spinal cause - due to the loss of previous inputs to the spine. This is known as deafferentation
6. central cause - due to changes in parts of the brain known as the cortex and thalamus
7. psychological cause - not usually regarded as the primary cause but stress, depression, etc. may contribute to the syndrome

It is likely that the cause is multifactorial - that is, similar symptoms may be seen from a variety of causes. This also explains why treatment is so difficult - one technique that works for a given patient may be an utter failure in another patient.

TREATMENT
Treatment of phantom limb pain is difficult - but should be undertaken as quickly as possible to prevent further changes to the nervous system (note that all the prevailing theories are based on some abnormal alteration of normal nervous system activity).

Medications often used include non-steroidal anti-inflammatories, narcotics, anticonvulsant medication, and antidepressants. Each of these have some reports of effectiveness - as well as reports of failures - in the literature. Each of these medications also has its own set of side effects.

There are many reports of the use of different nerve blocks in the literature. Success of nerve blocks seems to be only anecdotal and there is not a single block that is recommended as successful for a large majority of patients.

Regional blocks, intrathecal or epidural opioids, sympathetic blocks, and electrical nerve stimulators have also been tried with limited effectiveness. Again, most of this information is anecdotal via case reports. There is not a single technique that works all the time or even most of the time.

Lastly, it is important to recognize the importance of psychological assistance in many cases.

More radical therapy has been suggested and undertaken which involves ablation of various parts of the nervous system - whether in the brain or spinal cord. Each of these techniques have some support - studies on relatively small populations of patients and lacking long term follow-up. In many cases the results can easily be attributed to placebo effect. All of the techniques have significant potential complications.

NEW RESEARCH
It is clear that existing therapies have limited effectiveness - and what works for one person may not work for another. This makes the fact that research is ongoing and advancing even more important to the many people that have this problem. What is exciting is that research in this area is leading to results that might also help patients with other neurological injuries as well.

Researchers at Vanderbilt University recently reported findings that show that phantom limb pain seems to result from the brain's attempt to reorganize itself after an injury. When an injury such as amputation occurs, this results in a major interruption or loss of sensory input from the peripheral limb to the brain As a result, the brain seems to grow new nerve cells in an attempt to "re-wire" its existing pathways of nerve transmission. This builds on recent discoveries in neuroscience that show adult mammalian brains can grow new brain cells - something that was once thought impossible after early childhood.

The researchers at Vanderbilt traced nerve pathways in monkeys after arm amputation. Injectable tracer material was placed into the monkey's chin. Then the brains of these monkey were scanned to find these tracers. These tracers normally would show up only in the area of the brain responsible for sensation to the face. However, in the brains of the injured monkeys these tracers showed up as well in areas of the brain responsible for sensation to the arm and the hand.

This evidence was interpreted as showing that the brain, lacking normal sensory input for the hand and arm, re-routes the pathways to new areas of the brain. Thus the observation that patients report sensation in their lost arm when touched in other areas of their body (in this example - the face). This seems to be an attempt by the brain to heal itself or to "re-connect" broken pathways in some way.