Definition

Phantom pain refers to a painful sensation perceived in a body part that is no longer present subsequent to surgical or traumatic removal. It is most common after the amputation of a limb (i.e., phantom limb pain), but it has also been reported after the surgical removal of other body parts, such as breast, rectum, penis, testicles, eye, tooth, tongue, or lesion of peripheral or central nervous system [1]. Phantom limb pain is distinguished from stump pain, which is pain in the residual limb or stump, and phantom limb sensation, which is a nonpainful sensation of the absent part. Peripheral, spinal segmental, central, and psychological mechanisms are considered factors in the development of phantom limb pain, and an increasing number of studies with functional neuroimaging have suggested a central mechanism for phantom limb pain [2–5].

Although phantom limb pain is generally present within the first few days after an amputation, it can take several months or years to emerge. The reported prevalence of phantom limb pain differs considerably, ranging from about 40% to 90% [1,6]. However, phantom limb pain is less frequent in congenital amputation and loss of a limb early in childhood. The occurrence of phantom limb pain is independent of gender, age (in adults), level or side of amputation, dominance, and etiology of amputation.

In several reports, the intensity of pain remained constant but both the frequency and duration of pain attacks decreased significantly over time [7,8]. A small percentage of patients experienced a reduction in intensity of pain over time. Phantom limb pain leads to permanent disability in more than 40% of amputees, and pain persisting for more than 6 months is exceedingly difficult to treat.

Phantom limb pain has been reported to be significantly related to residual limb pain, physical activity, severity and duration of preamputation pain, noxious intraoperative inputs (such as pain brought about by cutting of tissues), acute postoperative pain, bilateral amputation, and lower limb amputation.

Symptoms

Pain is most prominent immediately after the operation; it is not static in nature and changes in quality over the years. Phantom limb pain is usually intermittent, but some patients report constant pain with superimposed exacerbations. The duration of an attack ranges from seconds or minutes to hours or days. Phantom limb pain is usually localized in distal parts of the absent limb, usually in the foot or hand.

The pain can be described as tingling, throbbing, aching, pins and needles, squeezing, stabbing, shooting, pinching, or cramping. Sometimes, the patients report that the amputated limb is positioned in a painful posture or that they sense spasms in the limb. The intensity as well as the quality of the pain varies greatly among patients from mild to severe. Phantom limb pain is triggered or worsened by physical (e.g., rainy weather, low temperature, prosthetic use, urination, defecation, reduced blood flow, and muscle tension), psychosocial (e.g., attention), and emotional (e.g., anxiety and stress) stimuli. Phantom limb pain is not relieved with position.

Physical Examination

Physical examination is generally unrevealing. However, patients can sometimes identify specific points on the residual limb that trigger phantom limb pain. Therefore the residual limb should be assessed for any sources of pain or trigger areas. The residual limb is examined for neuromas, cysts, bursae, bone spurs, or sites of excessive pressure. Other precipitating factors should be searched for, such as an ill-fitting prosthesis or mechanical stimulation.

Local problems, such as a herniated disc or spinal disease emitting sensations into the phantom limb or neuroma, can cause neuropathic pain. A comprehensive physical evaluation with particular attention to the neurologic examination, including strength, range of motion, muscle stretch reflexes, and muscle tone, should be done to rule out any concomitant central or peripheral neuropathic pain.

Functional Limitations

Functional complications of phantom limb pain include sleep disorders, interference with prosthesis training and use, reduction in walking ability, inability to return to work, change in employment status, and limitation of participation in social activities. Patients with phantom limb pain experience a greater degree of despair, more symptoms of depression, less satisfaction with social relations, poorer psychosocial adjustment, and poorer quality of life than amputees who are unaffected [9].

Diagnostic Studies

The diagnosis of phantom limb pain is generally made clinically on the basis of history and physical examination. Plain radiography and ultrasonography are performed for the diagnosis of underlying conditions, such as neuroma, abscess, bursitis, bone spur or fragment, or nerve entrapment. Magnetic resonance imaging, electrophysiologic tests, or laboratory tests may be indicated if other diagnoses are suspected.

Nerve block may be attempted as a diagnostic tool to identify candidates for specific procedures. Various pain scales and psychometric questionnaires are used to assess severity, treatment effect, and disability.