Clinical Syndrome

Phantom limb pain is the complaint by a patient of a painful sensation in an extremity that has been amputated. Phantom limb pain does not include the pain seen after spinal cord injury, nor does it include the pain seen after injury to peripheral nerves, lumbosacral or brachial plexus injury, or dorsal root avulsion when the body part has not been lost. All these conditions have similarities to phantom limb pain, on the basis of both clinical and physiologic evidence, but the differences are significant, and they should be analyzed and managed independently. Stump pains also must be differentiated from phantom limb pain; although they may be related, their management is different.
Virtually all amputees have phantom sensations; a much smaller percentage have phantom pain. Although phantom sensations and pain have been described after loss of body parts other than an extremity (breast, nose, bladder, etc.). It is probable that the neural substrates for all painful phantoms are similar and management strategies and results will not differ significantly, but there are not enough clinical reports about other types of phantom pain to permit meaningful statements.


The incidence of phantom limb pain has been reported to range from less than 1 to 50 percent in those patients who have lost a limb or a major portion thereof. Part of this variance can be explained by sampling techniques and part by variation in patient labeling of abnormal sensations. Studies based on patients referred to a treatment center or a particular physician are obviously biased by the inability to describe the population at risk. Surveys based on a complete group of amputees at risk suggest that phantom pain significant enough to cause the patient to seek medical care for the pain occurs in approximately 5 to 10 percent of the amputee population. Phantom limb pain appears to be more common in patients who lose their limb at an older age and in patients with affective or environmental factors which are likely to lead to chronic pain behavior independent of the type of injury. The etiology, severity, and location of extremity pain prior to amputation do not appear to influence the location or severity of phantom limb pain.

Neurophysiological Basis

The cause of phantom limb pain remains unknown; a variety of theories have been elaborated, but all lack verification. Any explanation of phantom limb pain must consider the relevant clinical phenomena. Phantom limb pain may be present immediately after injury or may develop weeks, months, or even years later. The phantom is usually described as foreshortened and in a distorted anatomic position. The pain may vary from continuous cramping, aching, and burning to electric shock-like and intermittent, even in the same patient; or it may be unchanging. Stress, anxiety, fear, or fatigue will usually increase the patient's complaints. Careful neurological assessment usually reveals that stimulation of the skin in normal areas remote from the lost part will often trigger phantom pain, as will percussion of stump neuromata. A painful phantom can exist with or without stump pain. A final problem is why only a portion of amputees develop phantom limb pain, even though almost all develop phantom limb sensation at some time after losing a limb.

Amputation of a body part clearly results in deafferentation of dorsal horn neurons and more rostral structures as well. Central reorganization of synaptic inputs has been shown to occur. Some neurons may remain deafferentated and become spontaneously hyperactive and supersensitive to transmitter substances. The behavior of wide-dynamic range neurons is known to change after peripheral nerve injury. Stump neuromata are electrically active

and may generate impulses that reach the spinal cord and cause the patient to describe sensations in the absent part. Altered sensory input may lead to errors in information processing in higher centers; phantom phenomena may be a cognitive error. Finally, a psychiatric theory holds that phantom limb pain is an ego phenomenon; there is no physiologic substrate but only an affective basis.

There can be no question that environmental and affective factors play a role in the patient's pain behavior and influence disability, drug utilization, and demand for health care. These factors certainly influence the patient's symptom manifestation, but there is not a shred of evidence that they suffice to explain why phantom limb pain occurs.

Phantom limb sensations and, rarely, pain have been described during regional or spinal anesthesia. They always disappear when the patient recovers from the block. As axonal silence, but not anatomic disruption, characterizes nerve blocks, this suggests that loss of afferent information has a central effect which can by itself generate phantom limb phenomena, including pain. Plasticity, both through the utilization of anatomically present but functionally silent synapses and through the growth of new connections after loss of afferentation, is the probable substrate of phantom limb pain. Neurons which have suffered major loss of input become spontaneously hyperactive; their output may be interpreted as pain by higher centers. The growth of new synaptic connections results in unusual sensory fields in the deafferented neurons. Downstream modulation can influence the firing of these neurons; hence the role of stress and relaxation in augmenting or diminishing phantom pains in some patients. As hyperactivity, supersensitivity, and new synaptic efficacy involve a wide array of sensory neurons, it should not be surprising that measures to alter the pain of acute tissue damage do not succeed in controlling phantom limb pain. The neural circuits involved in these two types of pain appear to be dissimilar based on the response to ablative surgical procedures and systemic opioids.

Natural History

Phantom limb pain may begin at the time of injury or may start after an interval of weeks, months, or even, rarely, years. Unlike phantom limb sensations, which are uniformly present immediately after loss of a limb and then frequently disappear over weeks or months, once phantom limb pain is present it is likely to persist for a prolonged period. The patient's complaints and utilization of health care frequently diminish over time. but this is often due to environmental and affective factors rather than spontaneous decrease in the phantom limb pain itself. In a few patients. however. phantom limb pain is a transient phenomenon. for reasons which are not understood. Phantom limb pain is usually a long-term management problem which persists in spite of attempts at medical management.

Therapeutic Choices and Long-Term Results

The choice of therapy has been based on the physician's preferences and resources. not the patients unique characteristics. How to select a therapy for a particular patient remains a mystery.                                         

The first step is to collect all the medical, psychological and environmental data available, Multidisciplinary pain clinics can often accomplish this goal more effectively than an individual physician or serial referrals to experts who may try to synthesize a meaningful comprehensive management plan. The second step is to address the psychological and environmental factors which, although not the cause of phantom limb pain, certainly can play a major role in the genesis of pain behavior. Strenuous efforts should be made to decrease and abolish the patient's use of narcotic. sedative-hypnotic and benzodiazepine drugs, which usually add to the patient's depression and fail to relieve this type of pain. Getting the patient back into normal daily activities by any means available is usually helpful. Although there is little hard evidence to support their efficacy. anticonvulsant medications have been widely used and they are reasonably safe. They should however, be discontinued if not clearly helpful. Antidepressants may be helpful in a nonspecific way: some have claimed success with the combination of a tricyclic antidepressant and a phenothiazine. Regional and local nerve blocks offer short-term relief, although occasional reports have described long-term benefits. Neurosurgical therapies have included ablative procedures from the stump neuromata to the forebrain and stimulation of peripheral nerves, spinal cord and brain. Some have been clearly shown to be rarely beneficial. Peripheral neurectomy. dorsal rhizotomy and sympathectomy rarely produce satisfactory results for more than a few weeks. Although cordotomy has often been performed, most patients show a recurrence of their pain within a year or two. Recent information about the presence of afferent fibers in the ventral roots has led to the modification of dorsal rhizotomy by the addition of ganglionectomy. Whether this will improve on the results of dorsal rhizotomy alone is not known at the present time. Thalamotomy rarely produces more than a year of pain relief. Although initial reports were glowing, excision of the parietal sensory cortex has also not produced long-term beneficial results in most patients. Reports on the efficacy of dorsal root entry zone lesions that destroy substantia gelatinosa and dorsal horn neurons have suggested a 50 percent long-term success rate: this operation has not yet stood the test of time.

Stimulation of peripheral nerves, spinal cord and brain all have their proponents: data on long-term efficacy are limited and not encouraging. The target area for brain stimulation should probably be the lateral thalamus-internal capsule and not the periaqueductal gray region.

As  all forms of surgical therapy carry some risk to the patient. They should not be offered to the patient until other therapeutic modalities have been tried. When surgery is elected. Results seem to be superior if all the psychological and behavioral issues are addressed in the same time frame as part of a comprehensive management process. Until the genesis of phantom limb pain is understood, it is unlikely that rational highly successful therapies will be available.

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