An innovative new treatment for Phantom Limb Pain.

By Nikki Steele

Did you know that the majority of people who have had a limb amputated still report feeling some sensation in the removed limb, such as itching or tingling? As many as 80% of amputees experience a type of this phantom limb pain. This can manifest as almost any sort of pain, such as stabbing, throbbing, or burning. Pain can last anywhere from minutes to hours to days, with some amputees in constant pain for decades.

While no one is quite sure what causes phantom limb pain, many experts suspect damaged nerves or scar tissue. Some also blame the mixed signals sent to the brain when an entire limb suddenly stops sending information. When the brain stops receiving input from a limb, it emits the most basic message it can to convey that something’s wrong: pain.

Because no one is certain of the cause of phantom limb pain, no single treatment has been proven to work without fail.

Medications and noninvasive therapies are often a doctor’s first suggestion. Oral drugs, like antidepressants, anticonvulsants or narcotics, are sometimes effective. Injected pain medications or steroids have also shown some success.

Spinal cord stimulation, during which the doctor inserts small electrodes into the spinal column, might also reduce pain. An electrical current is transmitted through the electrodes, hopefully blocking pain signals. Similar to spinal cord stimulation, deep brain stimulation employs electrical currents to block pain signals, but the currents are instead delivered directly into the patient’s brain. If all else fails, surgery might be suggested to remove scar tissue or damaged nerves. However, this risks worsening the pain if the surgery is unsuccessful or other complications arise.

Other therapies used for phantom limb pain are meant to trick the brain into thinking that the amputated limb still exists. For example, if a patient only has one remaining leg, a mirror box is used to make it appear that the missing leg is still there. Patients perform symmetrical exercises with the remaining limb while imagining that the phantom limb is performing the exercises simultaneously.

Recently, virtual reality (VR) programs have taken the place of traditional mirror therapy. Patients wear VR goggles while performing tasks with their remaining limb, but the goggles show the same tasks being performed by the missing limb instead. Alternatively, a patient can perform tasks in front of a screen equipped with motion tracking equipment and the screen shows the tasks being performed by the phantom limb.

These methods have had mixed results. Some patients report no difference in their phantom limb pain at all. Additionally, these therapies are useless for patients who have lost both arms or both legs, because there’s nothing for the mirrors to reflect or for the VR programs to mimic.

A new treatment for phantom limb pain takes this idea to new heights, while also providing a novel option for double amputee patients.

Max Ortiz-Catalan, a researcher at Chalmers University of Technology, recently carried out a case study with a patient who suffered from constant phantom limb pain for 48 years. The patient, who lost his arm below the elbow after a traumatic accident, had attempted drug therapy, acupuncture, traditional mirror therapy and even hypnosis, but his pain remained. Researchers attempted a new treatment method with the patient that was detailed in a recent article in Frontiers in Neuroscience.

For the study, electrodes were attached to the patient’s arm stump. The patient was instructed to attempt eight different movements with his phantom arm and hand, such as opening and closing his hand or flexing his wrist. These attempted movements “trained” the researchers’ computer program to translate myoelectric muscle signals in the stump and allowed the patient to control a superimposed arm on a screen. The superimposed arm responded in real time, fooling the brain into thinking it was controlling a real arm.

Not only does this method allow a patient to visualize the amputated limb, as in existing mirror and VR therapy, but it also engages the areas of the brain that control the limb’s movement. This, suggests Max Ortiz-Catalan, is the reason that this method is more effective at treating phantom limb pain. Even when the superimposed arm wasn’t visible, such as while playing a racing video game, the patient was able to achieve the same control over the arm and experienced the same benefits. Additionally, this therapy method’s function is based on muscle signals in the stump, rather than the reflection of a remaining limb, so it will work just as well for double amputees.

So far, the results are promising.

After 48 years of continuous phantom limb pain, the patient in Ortiz-Catalan’s case study reported being pain-free for 15-60 minutes after each therapy session. He experienced lessened pain at home between therapy sessions, and eventually reported experiencing periods of time at home with no pain at all for the first time since losing his arm. When asked about the perceived position of his missing hand, the patient stated that it was relaxed and semi-open, as opposed to the strongly clenched fist he’s experienced until now.

This therapy is similar in function to myoelectric prosthetics. Indeed, a myoelectric prosthetic utilizes electrodes on a patient’s skin to control movement of the prosthetic arm, just as electrodes allow patients control of the superimposed arm in Ortiz-Catalan’s study. While data is somewhat unclear, there is some suggestion that use of a myoelectric prosthesis could relieve phantom limb pain to some degree. However, these sorts of prosthetics are not very common. A great deal of training is involved, both for the doctor and for the patient. Also, a myoelectric prosthesis is extremely expensive, with prices ranging up to $100,000.

Ortiz-Catalan’s therapy method could provide a much more cost-effective means of treating phantom limb pain, especially if patients are able to do it at home. An at-home system has already been developed and is awaiting approval. The patient in the case study is using it regularly.

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