Sensors were placed on the stumps of 14 amputees to detect muscular activity for a missing arm in a recent study, where a specially designed video game incorporating an augmented reality limb was shown to reduce "phantom limb" pain.
On average the intensity, quality and frequency of phantom limb pain halved following the treatment.
Phantom limb pain occurs when amputees experience painful sensations which seem to come from their missing limb. Most amputees experience some pain after losing a limb, but for a third of cases it becomes very severe leading to poor quality of life, worse disability, poorer mental health and greater difficulty in prosthesis use than for amputees without phantom limb pain.
The condition is believed to be caused by the brain not adapting to the loss of a limb so the neurons for that area remain active and trigger pain.
There are few effective treatments for phantom limb pain. Surgery and drug treatments only provide limited pain relief while giving side effects, but studies have shown that mirror therapy can help alleviate pain. The therapy uses reflections of the unaffected limb to make it appear as though the patient is moving their missing limb. This allows them to "move" the limb out of painful positions and relieve pain. However, mirror therapy is not effective in all cases, including for double amputees.
The treatment in this study, called "phantom motor execution", is based on a similar idea to mirror therapy. In the study, researchers placed sensors on the patients' stumps to detect muscular activity for the missing arm. The signals were then fed into a computer that decoded and used them to create an active virtual arm on a computer screen, representing the missing limb.
There were three parts to the therapy, which involved patients training the virtual limb, driving a virtual race car around a track using their phantom movements and copying the movements of an on-screen limb with their phantom movements in 12 two-hour treatment sessions.
Patients rated the intensity, quality, and frequency of pain before each treatment session, as well as the intrusion of pain in sleep and activities of daily living. Once they completed all 12 sessions they had follow-up interviews one, three and six months after their treatment. The study is the first to follow-up patients with phantom limb pain as long as six months after their treatment.
The study revealed a 32 per cent reduction in the intensity of the pain, a 51 per cent reduction in pain quality and intensity and a 47 per cent reduction in its duration, frequency and intensity.
When looking at how this affected patients' day-to-day lives, the researchers found that there was a 43 per cent reduction in the amount that pain interrupted patients' daily activities and a 61 per cent reduction in how often pain interrupted their sleep.
The number of patients feeling constant pain reduced from 12 to 6 patients at six month follow-up and "stabbing" and "tiring/exhausting" pains in the phantom limb were statistically less common after the treatment. One patient on the trial did not report considerable improvement in his pain and another only found that it reduced flare-ups.
While promising, this trial was only small, and the findings need to be confirmed in a randomised clinical trial. There was no control group either, so the effect of treatment – although maintained at six months – could be due to the placebo effect. Also, the treatment would not be suitable for patients with nerve injuries and those who cannot move their stump.
Dr Melita Giummarra of Monash University said "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 Melita Giummarra also points out which patients will benefit more from this treatment approach, and whether it is feasible to set it up in the patients' own home, is unclear.
"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."