Phantom Movements in Virtual Reality Ease Phantom Limb Pain

Megan Brooks

December 08, 2016

"Exercising" a phantom limb using augmented reality and video gaming led to clinically meaningful and lasting reductions in phantom limb pain in a group of amputees who had experienced the condition for years and had not benefitted from multiple other treatments, researchers from Sweden report.

The treatment, called "phantom motor execution," was invented by Max Ortiz-Catalan, PhD, from the Department of Signals and Systems, Chalmers University of Technology, Gothenburg, Sweden, and further developed with his multidisciplinary team over the past several years.

Patient using phantom motor execution system

It uses neuromuscular signals from the amputated limb to control augmented and virtual environments. Electrical signals in the muscles are picked up by electrodes placed on the patients' arm stump. These signals are then fed into a computer that decodes and uses them to create a virtual arm on a computer screen, representing the missing limb. A webcam allows the patient to see him or herself moving the virtual limb on the screen. This allows the patient to reactivate areas of the brain that were used to move the arm before it was amputated, which might be the reason that the phantom limb pain decreased, the researchers say.

In a study, 14 patients with upper-limb amputations and intractable chronic phantom limb pain were trained to move the virtual limb and drive a virtual race car around a track using their phantom movements in 12 two-hour treatment sessions.

The study was published online December 1 in The Lancet. It includes a video describing how phantom motor execution works.

"We selected the most difficult cases from several clinics," Dr Ortiz-Catalan said in a university statement.

"We wanted to focus on patients with chronic phantom limb pain who had not responded to any treatments. Four of the patients were constantly medicated, and the others were not receiving any treatment at all because nothing they tried had helped them. They had been experiencing phantom limb pain for an average of 10 years," he added.

The research team assessed changes in intensity, frequency, duration, quality, and intrusion of phantom limb pain using the Numeric Rating Scale, the Pain Rating Index, the Weighted Pain Distribution Scale, and a study-specific frequency scale before each treatment session and at follow-up interviews 1, 3, and 6 months after the last session.

After 12 sessions, patients showed "statistically and clinically significant" improvements in all metrics of phantom limb pain, the researchers report.

Phantom limb pain decreased from pretreatment to the last treatment session by 47% (P = .001) on the Weighted Pain Distribution Scale, 32% (P = .007) on the Numeric Rating Scale, and 51% (P = .0001) on the Pain Rating Index.

There was also a significant 43% (P = .004) reduction in the extent to which pain interrupted patients' daily activities and a 61% (P = .001) reduction in how often pain interrupted their sleep.

By the last treatment session, 2 of the 4 patients who were continuously medicated for at least 2 years reduced the dose of medication by 81% (gabapentin, from 1600 mg to 300 mg) and 33% (pregabalin, from 225 mg to 150 mg).

The improvements remained 6 months after the last treatment.

"Phantom limb pain is a difficult condition to treat that can seriously hinder patients' quality of life," Dr Ortiz-Catalan said in a statement. "The results from our study suggest that it may be useful to 'exercise' the phantom limb. Our treatment offers an engaging way to do this while also providing a non-invasive and non-pharmacological treatment which was found to reduce chronic pain with no observed side effects."

"Promising Data"

The researchers acknowledge that the study was small and the findings need to be confirmed in a randomized clinical trial. They also note that phantom motor execution would not be suitable for patients with nerve injuries and those who cannot move their stump.

In addition, the possibility of a placebo effect cannot be disentangled in this study because of the lack of a control group. But Dr Ortiz-Catalan told Medscape Medical News, "We believe it is unlikely that placebo was a strong reason of improvement because placebo effect doesn't last very long, and our patients retained the improvements after 6 months. With that being said, we are about to start a large randomized clinical trial in 5 countries."

He also said he believes this technology can become widely available. "I have made several parts open source already. We have developed a portable system that a few patients are using at home. All that is needed is a computer, a webcam, and our electronics and software for decoding human motor volition," Dr Ortiz-Catalan said.

Writing in a linked Comment, Melita Giummarra, PhD, from Monash University, Melbourne, Australia, says the authors have presented "promising data that support the clinical feasibility and effectiveness of machine learning and augmented reality in the treatment of phantom limb pain."

However, several factors are "likely to affect delivery of this treatment in clinics, particularly the cost and expertise for setting up the equipment and software, and the training required to run and tailor the programme for individual patients," Dr Giummarra writes.

"Moreover, which patients will benefit more from this treatment approach, and whether it is feasible to set it up in the patients' own home, are unclear. The fact that the authors have made the algorithms and software freely available will no doubt facilitate replication of the treatment in independent research groups, which will in turn facilitate the validation of this therapy," she notes.

"Studies are now required to examine the magnitude of effects compared with alternative treatments, or placebo, to determine whether this treatment warrants the investment in resources and training that would be required to deliver this therapy in practice," Dr Giummarra says.

The study was funded by Promobilia Foundation, VINNOVA, Jimmy Dahlstens Fond, PicoSolve, and Innovationskontor Väst. Dr Ortiz-Catalan and three coauthors were partially funded by Integrum AB, a for-profit organization, which might commercialize an improved version of the technology described here. Dr Giummarra has disclosed no relevant financial relationships.

Lancet. Published online December 1, 2016. Abstract, Comment

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