Weir Mitchell coined the term phantom-limb pain in 1872. It describes the pain in the body part that is no longer present, which occurs in 50–80% of all amputees. Pain can have several different qualities, such as stabbing, throbbing, burning, or cramping. It seems to be more intense in the distal portions of the phantom limb. This pain may be related to a certain position or movement of the phantom and may be elicited or exacerbated by a range of physical factors (e.g., changes in weather or pressure on the residual limb) and psychological factors (e.g., emotional stress).
It is more likely to occur if the individual had chronic pain before the amputation. Pain in the phantom is often similar to the pain felt in the limb before amputation. Phantom pain is most common after the amputation of an arm or leg, but it may also occur after the surgical removal of other body parts, such as breast, rectum, penis, testicle, eye, tongue, or teeth. About 30% of persons with amputation report the feeling of telescoping, i.e., the retraction of the phantom towards the residual limb and in many cases, the disappearance of the phantom into the limb. This may be accompanied by a shrinking of the limb. Recent evidence suggests that telescoping is associated with more phantom-limb pain.
Phantom-limb pain is commonly confused with pain in the area adjacent to the amputated body part. This pain is referred to as residual-limb or stump pain. Patients may report severe, knife stabbing or sharp pain in at the end of the amputated limb. Formation of neuroma or pressure-lesions of the stump may exacerbate the stump pain. Physical examination may reveal the existence of a neuroma. It is usually very sensitive to touch or pressure. However, stump pain may coexist with phantom limb pain.
Changes along the neuroaxis may contribute to the experience of phantom-limb pain. Spinal mechanisms are characterized by increased excitability of the dorsal-horn neurons, reduction of inhibitory processes, and structural changes at the central nerve endings of the primary sensory neurons, interneurons, and the projection neurons. Supraspinal changes related to phantom-limb pain involve the brainstem, the thalamus, and the cortex.
Reorganization of the somatosensory cortex of the human cerebral cortex in amputees has been supported by findings from several imaging studies. People with arm or hand amputations show a shift of the mouth into the hand representation in the primary somatosensory cortex. Studies in human amputees have shown that reorganizational changes also occur at the thalamic level and are closely related to the perception of phantom limbs and phantom-limb pain. Neuroma in the stump may be more responsible for stump pain than phantom limb pain.
However, abnormal input originated from a neuroma in the residual limb may increase the amount of central reorganization, enhancing the chance of phantom-limb pain. Psychological factors also play a role in the modulation of phantom-limb pain. Phantom-limb pain may also be exacerbated by stress. Patients who lack coping strategies, fear the worst, or receive less social support, tend to report more phantom-limb pain.
Treatment for phantom limb pain has been difficult. Although tricyclic antidepressants and sodium-channel blockers are treatments of choice for neuropathic pain, there have been no controlled studies of these agents for phantom-limb pain. Opioids, calcitonin, and ketamine have been proven to be effective in reducing phantom-limb pain in controlled studies. Transcutaneous nerve stimulation (TENS) may have a minor effect on phantom-limb pain. A maximum benefit of about 30% has been reported from treatments such as local anesthesia, sympathectomy, dorsal-root entry-zone lesions, cordotomy, rhizotomy, neurostimulation methods, or pharmacological interventions such as anticonvulsants, barbiturates, antidepressants, neuroleptics, and muscle relaxants. Use of a myoelectric prosthesis may alleviate cortical reorganization and phantom-limb pain. Deep brain stimulation also has been reported to treat phantom limb pain.