Phantom limb

Definition

Phantom limb is the term for abnormal sensations perceived from a previously amputated limb. The abnormal sensations may be painful or nonpainful in nature. It is presumed to be due to central and peripheral nervous system reorganization as a response to injury. Phantom limb pain is often considered to be a form of neuropathic pain, a group of pain syndromes associated with damage to nerves.

Description

Phantom limb syndrome was first described by Ambroise Pare in 1552. Pare, a French surgeon, noticed this phenomenon in soldiers who felt pain in their amputated limbs. Mitchell coined the term "phantom limb" in 1871. Phantom limb syndrome can be subdivided into phantom limb sensation and phantom limb pain. Stump or residual limb pain refers to pain that may persist at the residual site of amputation and may be grouped under phantom limb syndrome as well.

The onset of pain after amputation usually occurs within days to weeks, although it may be delayed months or years. Pain may last for years, and tends to be intermittent rather than constant. Pain may last up to 10–14 hours a day and can vary in severity from mild to debilitating The abnormal "phantom" sensations and pain are usually located in the distal parts of the missing limb. Pain and tingling may be felt in the fingers and hand, and in the lower limbs, in the toes and the feet.

Demographics

The incidence of phantom limb pain is estimated in 50–80% of all amputees. Phantom limb sensation is more frequent and occurs in all amputees at some point. There is no known association with age, gender, or which limb is amputated. Studies have shown a decreased incidence of phantom limb syndrome in those born without limbs versus actual amputees.

Causes and symptoms

The exact etiology of phantom limb pain is unknown. Phantom limb is thought to be secondary to the brain plasticity and reorganization. The human brain has an enormous capacity to alter its connections and function in response to everyday learning or to the setting of injury. These processes of reorganization may occur in retained nerves in the amputated limbs, the spinal cord, or various parts of the brain, including the thalamus and the cerebral cortex. Although phantom pain is presumably a result of a response to amputation injury, phantom limb pain may occur in nonamputees with spinal cord damage causing loss of sensation. This suggests that the phantom limb phenomenon may be a result of damage to pathways responsible for painful sensation in general. Research studies in primates and patients with limb amputation have shown that after amputation, the area of the brain that is responsible for processing the sensations from the missing limb are taken over by areas neighboring the missing limb.

Patients may feel a variety of sensations emanating from the absent limb. The limb may feel completely intact despite its absence. Nonpainful sensations may include changes in temperature, itching, tingling, shock-like sensations, or perceived motion of the phantom limb. The limb may feel as if it is retracting into the stump in a phenomenon called telescoping. Painful sensations include burning, throbbing, or stabbing in nature. Touching the remaining stump may elicit sensations from the phantom. The quality of the pain may change over time and may not remain constant. Patients may also feel pain from the retained stump itself. Stump pain is often associated with phantom limb sensations and may be related in etiology.

Diagnosis

The diagnosis of phantom limb is a clinical one. A history of previous limb amputation and the subsequent symptoms of abnormal sensations from the missing limb are key to the diagnosis. Spinal cord damage affecting pathways mediating sensation may also be associated with phantom limb. There are no imaging or clinical tests useful in diagnosing phantom limb.

Treatment team

The treatment team for phantom limb pain may involve the participation of neurologists, pain specialists, physical therapists, neurosurgeons, or rehabilitation specialists. Neurologists and pain specialists may help in prescribing medications to treat the phantom limb pain. Physical therapists may help to facilitate and maintain mobility. Neurosurgeons may perform surgery to place electrical nerve stimulators in the spinal cord or lesion procedures to help treat the pain.

Treatment

There are few controlled clinical studies on phantom limb treatment, and therefore no consensus on the best treatment. Treatment is directed towards the management of painful symptoms. Nonpainful symptoms rarely require treatment. Treatment for phantom limb pain involves the use of medications, nonmedical, electrical, and surgical therapy.

Medical treatment of phantom limb pain involves agents typically used for neuropathic pain. Medications such as anticonvulsants , muscle relaxants, and antidepressants may be tried. Opiate medications have also been used. Ketamine, an anesthetic agent, or calcitonin has been shown to be effective in some clinical studies.

Various electrical and nonmedical treatments may be tried. Trancutaneous electrical nerve stimulation (TENS) and biofeedback may be used. Massage, ultrasound, and acupuncture modalities may be tried as well. Training patients to discriminate sensory signals in the stump appears to be helpful in reducing pain. In research studies, allowing individuals to see a reflection of the normal, intact limb moving in the position of the amputated limb helped alleviate symptoms of phantom limb pain.

Surgical treatments for phantom limb pain are limited in benefit. Lesions of various pain centers in the spinal cord and brain can be performed, and may provide short-term relief on most occasions.

Recovery and rehabilitation

Prospective studies of phantom pain show that in two years, many amputees will experience a reduction of symptoms. Physical and occupational therapists may help in the treatment of phantom limb pain by maintaining range of motion and mobility.

Clinical trials

There are ongoing clinical trials conducted by the National Institutes of Neurological Disorders and Stroke (NINDS) studying touch perception in patients with upper limb amputation.

Prognosis

The prognosis for phantom limb varies from individual to individual. Medical treatment shows the most benefit in treating symptoms. Some studies show that in a two-year period, many amputees will experience a reduction or disappearance of their phantom limb pain. The results of the studies are somewhat limited due to the heterogeneity of the populations studied.

Special concerns

Phantom limb may have a chronic course and may lead to feelings of depression or anxiety. These feelings may require treatment by a psychiatrist. Patients with phantom limb should continue to be active and participate in community and social activities. There are various support groups for amputees.

Resources

BOOKS

Ramachandran, V. S., and Sandra Blakeslee. Phantoms in the Brain: Probing the Mysteries of the Human Mind. New York: William Morrow, 1998.

"Phantom Pain." Chapter 16. In Practical Management of Pain, 3rd edition, edited by P. Prithvi Raj. St. Louis, MO: Mosby 2000.

PERIODICALS

Flor, H. "Phantom-limb Pain: Characteristics, Causes, and Treatment." Lancet Neurology 1 (2002): 190–195.

Hill, A. "Phantom Limb Pain: A Review of the Literature on Attributes and Potential Mechanisms." Journal of Pain and Symptom Management 17 (February 1999): 125–142.

Nikolajsen, L., and T. S. Jensen. "Phantom Limb Pain." British Journal of Anaesthesia 87 (2001): 107–116.

OTHER

National Institutes of Neurological Disorders and Stroke (NINDS). Pain: Hope Through Research. NIH Publication No. 01-2406. Bethesda, MD: NINDS, 2001.

ORGANIZATIONS

American Chronic Pain Association. P.O. Box 850, Rocklin, CA 95677-0850. (916) 632-0922 or (800) 533-3231; Fax: (916) 632-3208. ACPA@pacbell.net. <http://www.theacpa.org>.

American Pain Foundation. 201 North Charles Street, Suite 710, Baltimore, MD 21201. (410) 783-7292 or (888) 615-7246; Fax: (410) 385-1832. info@painfoundation.org. <http://www.painfoundation.org>.

The Pain Relief Foundation. Clinical Sciences Centre, University Hospital Aintree, Lower Lane, Liverpool, L9 7AL, UK. 0151.529.5820; Fax: 0151.529.5821. pri@liv.ac.uk. <http://www.painrelieffoundation.org.uk/index.html>.

Peter T. Lin, MD

phantom limb After loss of a limb more than 90% of patients experience a vivid illusory persistence of the limb in the form of a ‘phantom’. The phantom appears immediately in the majority and after a delay of a few days or weeks in the rest. It can then persist for months, years, or even decades.

The phantom often has a ‘habitual’ position (for example a phantom arm may be partially flexed at the elbow with the forearm pronated) but spontaneous changes in its posture are common. The extent to which voluntary and involuntary movements occur in the phantom varies from patient to patient.

Phantoms can appear not only for a limb, but for almost any body part: breast, penis, face, jaw, or even for internal organs. Patients can experience phantom menstrual cramps after hysterectomy, the spasmodic pain of appendicitis after appendectomy, or ulcer pains after gastrectomy; even phantom erections have been reported after the penis is removed.

The term ‘phantom limb’ was coined in 1872 by Silas Weir-Mitchell, who published the first paper on this subject anonymously for fear of ridicule by his peers. Since then a fascinating clinical lore has built up and there have been hundreds of case studies. But a systematic scientific study began only towards the end of the twentieth century. Animal studies have combined with systematic psychophysical testing and brain imaging in human amputees, to move the study of phantom limbs from vague clinical phenomenology into an era of experimental research.

The phantom is enhanced by the presence of referred sensations: stimuli applied to other parts of the body that are experienced as arising from the phantom. For example, after arm amputation, touching the face will often evoke precisely localized sensations in the phantom fingers, hand, and arm. The points that evoke such sensations are topographically organized (consistently ‘mapped’) and the referral is modality-specific, meaning for instance that heat on the face will elicit heat in the phantom digits and that vibration is felt as vibration. This face-to-phantom-hand referral probably occurs because the face is right next to the hand in the complete map of the whole body's skin surface on the somatosensory region of the cerebral cortex (described as a result of electrical brain stimulation studies by neurosurgeon Wilder Penfield in the 1930s).

The sensory input from the face skin ordinarily activates only the face area of the cortex, but if the adjacent hand cortex is denervated (cut off from any sensory input), then the input from the face starts activating the original hand area as well. This is a striking demonstration of plasticity in the adult human brain: that new neural links can be made. The observation also implies that even though the hand area is now being activated by sensory input from the face skin, higher brain centres still continue to interpret the signals as arising from the hand. Changes in somatosensory cortex topography — occurring over distances of 2–3 cm — have also been shown in the same patients using functional brain imaging techniques — especially magnetoencephalography (MEG); this allows researchers to correlate perceptual phenomena described by the patient (such as referred sensations) with the anatomical sites of activity.

These demonstrations of ‘plasticity’ in the adult brain can also be seen in monkeys in which one arm has been deafferented (all sensory nerve pathways interrupted). Indeed, the human studies were inspired by the animal experiments.

Sensations may also be referred the other way around between the hand and the face, after the trigeminal nerve that supplies the face is cut — an occasional last resort for severe neuralgia. The patient then has a map of the face on the hand. Again, after leg amputation, stimuli applied to the genitals are referred to the phantom foot. This is consistent with the representation of the foot next to the genitals in Penfield's original maps of the somatosensory cortex.

Vivid ‘movements’ in the phantom are reported by some patients. These sensations are very ‘real’ to the patient — so much so that volitional movements of the phantom hand can interfere with a dissimilar movement performed by the normal hand, in a manner identical to the interference between hands that occurs in normal people. The patient cannot for example rub his belly with his real hand while ‘tapping his head’ simultaneously with the phantom. These movement sensations in the phantom probably arise from ‘feed forward’ or corollary discharge: when the motor areas of the patient's cerebral cortex send a command to the missing arm, a copy of the command is sent to the cerebellum and parietal lobes so that intention can be compared with action. These commands may initially be experienced as movements, but the prolonged absence of visual confirmation, and of sensory input from muscles and joints of the missing arm, may lead eventually to a ‘paralysed’ phantom that the patient can no longer move.

Sometimes the phantom will develop a painful clenching spasm and the patient cannot voluntarily ‘unclench’ his imagined fist even with intense effort. If a mirror is propped up vertically on the table, in the plane that separates the right from the left half of the body, and if the patient views the reflection of his normal hand in the mirror, the reflection of the hand is seen superimposed on the felt position of the phantom — giving the visual illusion that the phantom has been resurrected. If he now moves the normal hand the phantom is suddenly ‘animated’ and is vividly felt to move. Sometimes this can lead to the unclenching of a previously clenched, painful phantom, suggesting a promising new therapeutic approach for phantom pain. The usefulness of the procedure requires detailed evaluation, but the illusion suggests that a great deal of interaction can occur between visual sensations and those from the limb.

Phantom limbs are also seen in a small percentage of patients with congenitally missing arms or legs, suggesting that at least the basic scaffolding for one's body image may be innately specified. Indeed, the phenomenon provides a valuable opportunity to investigate how nature and nurture interact in the construction of body image by the brain. A patient with leprosy whose hand gets whittled away gradually with progressive sensory loss does not have a phantom hand. But if the stump is then amputated, what emerges is not a phantom stump but a whole phantom hand. It is as though the original image of the hand had survived but was inhibited by the stump, only to be resurrected when the stump is amputated!

In summary, at least four factors seem to contribute to the vividness of the phantom: stump neuromas (nodules of scar tissue and curled up nerve endings); remapping of somatosensory areas in the brain leading to referred sensations; a genetically-specified ‘body image’ that partially survives limb loss; and monitoring of corollary discharge associated with motor commands sent to the phantom. The combination of systematic psycho-physical testing with brain imaging techniques in human amputees, together with animal studies on somatosensory remapping, has rapidly advanced the study of phantom limbs. Such research will allow investigation not only of how the brain remodels itself continuously in response to bodily injury, but also how the activity in the brain somatosensory ‘map’ leads to conscious experience of body image and somatic sensations.

J. Vaid, and V. S. Ramachandran

Bibliography

Melzack, R. (1992). Phantom limbs. Scientific American, 266, 120–6.
Ramachandran, V. S. (1998). The perception of phantom limbs: the D. O. Hebb lecture. Brain, 121, 1603–30.

phantom limb (fan-tŏm) n. the sensation that an arm or leg, or part of an arm or leg, is still attached to the body after it has been amputated. Pain or other sensations may seem to come from the amputated part.