In the US, surgeons perform about 185,000 limb amputations each year, and the majority of these individuals are left with some sort of post-amputation pain. Unfortunately, post-amputation pain syndromes have proven very difficult to treat. A variety of treatments are available, but most of these have not had high quality clinical trials, and only appear beneficial in some cases.

Post-amputation pain falls into two distinct categories: phantom limb pain and residual limb pain. Phantom limb pain refers to unpleasant and painful sensations that seem to the patient to originate from the lost limb, even though the individual consciously understands that the limb is no longer there. One study found that the incidence of phantom limb pain might be as high as 85%. The pain can vary from sharp and shooting sensations to dull, squeezing, or cramping sensations.

An amputee may also perceive residual limb pain (sometimes called “stump” pain) in the part of the body that remains after amputation. It is typically a sharp, burning pain, with a reported incidence of up to 74%. Often, an individual experiences both types of pain syndromes. These pain syndromes are separate from other types of pain an amputee might experience, such as those arising from an incorrectly fitted prosthetic device.

Multiple mechanisms appear to play a role in the development of post-amputation pain, though not all mechanisms may be present in every individual patient. For example, in the brain itself, reorganization in the somatosensory cortex is thought to play a role (this brain area is partly responsible for “mapping” sensations onto the relevant body part). Evidence also points to a role for the spinal cord in post-amputation pain, specifically in a region known as the dorsal horn, which normally receives the incoming sensory information. In some cases, the nerves which were severed in the amputation also appear to contribute to the condition.

Local injection therapy is one of the current mainstays of treatment for individuals with post-amputation pain; for example, injection of the local pain blocker lidocaine at the amputation site. This is more effectual for residual limb pain than for phantom limb pain, and even then the effect is usually temporary. 

Drug treatment is another option. NMDA antagonists like ketamine, opioid drugs like morphine, calcitonin, and anticonvulsant drugs have all shown mixed results in studies. Various types of surgical treatment are sometimes attempted, such as peripheral nerve stimulation, motor cortex stimulation, and deep brain stimulation. These treatments are still experimental, but motor cortex stimulation in particular looks like it may prove beneficial. One study found 53% of phantom limb patients were successfully treated with this method.

Mirror therapy provides another intriguing and cost-effective mode of treatment. In this approach, a mirror is placed adjacent to an intact limb, providing the illusion that the amputated limb is present. Some subjects report immediate lessening or elimination of pain, and multiple studies have demonstrated at least short-term pain reduction using this simple technique. It is believed that this feedback can help somatosensory pathways reorganize, thus reducing pain.

Future developments may involve better classifying patients into subgroups, which may show different response levels to different treatments. Many patients will continue to need multimodal, individualized treatment. Researchers hope to develop better and more proven treatments, partially through a more complete understanding of the multiple potential causes of the condition. New drugs, such as anti-nerve growth factor antibodies, are currently under early development, and may one day provide a new class of medications for the physician’s toolkit.

References

Chan BL, Witt R, Charrow AP, Magee A, Howard R, Pasquina PF, Heilman KM, & Tsao JW (2007). Mirror therapy for phantom limb pain. The New England journal of medicine, 357 (21), 2206-7 PMID: 18032777

Hsu E, & Cohen SP (2013). Postamputation pain: epidemiology, mechanisms, and treatment. Journal of pain research, 6, 121-36 PMID: 23426608

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