Exploring Phantom Limb Pain

First described more than 500 years ago, phantom limb pain (PLP) is a common disorder today; as many as 50% to 80% of patients who undergo amputation report experiencing pain in the missing body part._¹ Although it is easy to recognize and diagnose, its cause remains unclear and it can be difficult to manage successfully. Perhaps that's why health care professionals often do not address it. A survey by Hanley and associates,² for example, found that 53% of patients with PLP and 38% with severe PLP had never been treated for the disorder.

Why this problem develops in certain patients remains unclear, although animal studies indicate that there may be a genetic predisposition to PLP.³ PLP most commonly occurs after the amputation of an extremity, but it also has been reported after surgical removal of other parts of the body, most notably after a mastectomy.

At one time, PLP was thought to be primarily a psychological problem that reflected both the patient's grieving over the loss of the limb and his or her desire to believe that the limb was still present; however, psychological factors do not appear to be the primary cause. Ephraim and colleagues⁴ did find the presence of depression to be a predictor of the severity of PLP, although it was similarly associated with residual limb and back pain in amputees.

Current concepts of causation center primarily around the role of the peripheral and central nervous systems.⁵ Amputation results in a disruption of normal peripheral nerve activity. The traumatic injury to the nerves may cause abnormal ectopic discharges that are perceived as pain at the level below which the nerves were severed. Formations of neuromas in the remaining portion of the limb may also play a role, although it has been noted that PLP frequently occurs before there has been sufficient time for neuromas to appear. Activation of the sympathetic nervous system is also a possible cause. Centrally, changes may occur in both the spinal cord and brain following amputation. Injuries to the peripheral nerves can result in changes in synaptic responsiveness in the dorsal horn that can lead to increased excitability of the neurons in the dorsal horn and decreased inhibitory processes.⁶ It appears that following amputations, there may be changes in the brainstem, thalamus, and cortex caused by abnormal peripheral input. However, it is unclear whether these changes are involved in the causation of PLP or are secondary to it.

Since there are no physical changes in PLP, the diagnosis is made solely on the basis of the patient's self-report. Because of fears that the presence of pain in a missing body part is irrational and may indicate that one is “losing one's mind,” it is important to assure patients that it is a very real phenomenon. It is also always important to differentiate PLP from stump pain, which commonly occurs after amputation and is often much easier to manage.

When describing PLP, patients report a variety of sensations, including burning, shooting, and aching pains as well as tingling and pins-and-needles sensations. The pain is usually intermittent and most often felt in the distal parts of the missing limbs.¹

There is no single best treatment for PLP. Multiple therapies have been used with mixed success, and there are a limited number of good controlled studies. Unfortunately, there are no factors for predicting which therapy is likely to benefit a particular patient.