Meredith Wright Phantom limb pain (PLP) is reported in nearly 80% of patients with missing limbs, yet the causes are still not fully understood. Recent research on the topic has helped to increase our knowledge of PLP, but the varying nature of the condition makes it difficult to define and treat. Patients often experience different sensations described as tingling, throbbing, piercing, or pins and needles. Some patients have reported experiencing these sensations immediately following an amputation, while others do not experience any phantom pain until years after the surgery. In addition to varying times of onset, the periods of pain onset may differ from patient to patient, ranging from a few weeks to any number of years (Subedi et. al. 1-2).
Risk Factors for Phantom Limb Pain
Female Sex
Upper extremity amputation
Presence of pre-amputation pain
Residual pain in remaining limb
Time after amputation
While the mechanisms of PLP are still debated, increased focus on the condition has led to the revelation of some interesting trends. Phantom limb pain occurs more often and with greater intensity in females than in males; upper extremity amputations have a greater tendency for PLP than lower extremity amputations; and patients who experience pain in their limb prior to its amputation are more likely to experience PLP after amputation. In the past, PLP was characterized as a psychiatric illness, but the mentality among physicians and researchers is changing. Research is now aimed at discovering the physiological mechanisms of PLP instead of dismissing the condition as purely psychological (Subedi et. al. 2).
Theories
Numerous theories exist in regards to the causes of PLP, and most experts believe that a combination of the proposed mechanisms may actually be responsible for the pain that patients experience. The most cited cause of PLP in recent years is associated with changes that occur in the brain when there is a lack activity in a certain region, such as the portion of the brain that controls a missing limb. When a portion of the brain is not being used, neighboring sensory or motor areas can take over. This process is termed cortical reorganization, and can partly explain why patients may still feel sensations in a missing limb (Subedi et. al. 2).
Another theory, the peripheral mechanism, explains PLP as the result of spontaneous discharges from neuromas that form in peripheral nerves following an amputation. A neuroma is a proliferation of cells that develop after injury to a nerve. This ball of nerve cells acts abnormally, and could result in stump or phantom pain (Subedi et. al. 2).
One last interesting theory attributes painful sensations to the incongruence between motor intention and sensory feedback in the brain. While a patient may feel as if his or her phantom arm is extending to reach for a cup, vision and other sensory feedback tells the brain that the limb is not present. Some experts propose that the brain interprets this conflict by sensing pain in the phantom limb (Jerrell). In reality, PLP is likely due to a combination of the proposed mechanisms and differs among the various types of patients.
Treatments
When treating PLP, each case must be addressed using trial and error as no single treatment has proven to be the best for all types of patients (Jerrell). While numerous patients have found success using some of the available therapy options, it is up to the patient and his or her provider to find what works best on a case-by-case basis.
Many different types of pain medications and anti-depressants have been used in the past, but studies have shown mixed results. NSAIDs such as Motrin or Advil were found to be the most common medications used to treat PLP, likely because they are over-the-counter and have few side effects (Subedi et. al. 3).
Transcutaneous Electrical Nerve Stimulation (TENS) is another noninvasive treatment that is becoming more common, even though only a few studies have shown its effectiveness. TENS therapy uses electrodes placed on the skin to apply current to the affected nerves. Stimulation may reduce pain by blocking pain signals from reaching the brain, or by prompting the body to produce neurotransmitters that act as natural painkillers (Desantana et. al. 492-494).
Another treatment – mirror therapy – has shown significant benefit in some patients, particularly lower 
leg amputees. During mirror therapy, the patient watches the intact limb move in a mirror (placed between their legs or arms), such that it appears that the missing limb is present. By “seeing” and feeling the phantom limb moving, this therapy attempts to resolve conflicting visual and proprioceptive sensations in the brain (Jerrell).
In summary, phantom limb pain is still elusive and requires more research to develop better definitions and treatments for the condition. It is a disability suffered by a large percentage of amputees, yet there are still no definitive answers to some fundamental questions in regards to its causes and treatments. In recent years, our understanding of PLP has grown and evolved, leading to numerous theories attempting to provide an explanation for the phenomenon. At the moment, however, no treatment has proven effective for every type of patient. PLP must be dealt with using a trial and error approach to find the treatment that is best for each individual patient.
(Image – US Defense Department photo, Donna Miles)
Guest blogger – A. Allen
Works Cited
Subedi, Bishnu, and George T. Grossberg. “Phantom Limb Pain: Mechanisms and Treatment Approaches.” Pain Research and Treatment (2011): 1-8. Web. 24 June 2015. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3198614/>.
Jerrell, Mary L. “Cause of Phantom Limb Pain Still Elusive.” Healio O&P News. O&P News, 1 Feb. 2012. Web. 24 June 2015. <http://www.healio.com/orthotics-prosthetics/prosthetics/news/print/o-and-p-news/{3bb02d3c-6b4a-4b5d-bfbc-f0027e7191c9}/cause-of-phantom-limb-pain-still-elusive?sc_trk=internalsearch>.
Desantana, Josimari M., Deirdre M. Walsh, Carol Vance, Barbara A. Rakel, and Kathleen A. Sluka. “Effectiveness of Transcutaneous Electrical Nerve Stimulation for Treatment of Hyperalgesia and Pain.” Curr Rheumatol Rep Current Rheumatology Reports 10.6 (2008): 492-99. Web. 24 June 2015. <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2746624/>.
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