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Most amputees experience some “phantom” pain that seems to come from
a lost limb. For about a third of them, it becomes so severe that it
worsens their disabilities, makes it harder for them to use
prosthetic limbs and impacts their mental health and quality of
life, researchers note in The Lancet.
The experiment tested what researchers call “phantom motor
execution,” using virtual reality to give participants the sensation
that they’re moving a missing limb.
“When the patient aims to move their missing limb, muscles at the
stump produce traces of electrical activity that we use to decode
the intended phantom limb movement,” said lead study author Dr. Max
Ortiz Catalan of Chalmers University of Technology in Gothenburg,
Sweden.
“We then show this movement to the patient in real-time with
augmented reality and other virtual environments,” Ortiz Catalan
said by email. “This makes the patient use brain areas dedicated to
motor execution that were previously neglected, and potentially
entangled with pain perception circuitry.”
The study included 14 patients who began experiencing phantom limb
pain soon after they had an arm amputated. They had been amputees
for between two and 36 years and had not benefited from other
treatments.
For the experimental treatment in the study, researchers placed
sensors on the patients' stumps to detect nerve signals that would
control muscular activity for the missing arm. The sensors fed
signals into a computer that decoded and used them to create an
active virtual arm on a computer screen, representing the missing
limb.
Participants received training on how to use their virtual arms to
make so-called phantom movements in the game. Then they drove a
virtual car around a racetrack using phantom movements and played
another game copying movements of an on-screen arm with movements of
their own virtual arms.
Altogether, they completed a series of 12 two-hour treatment
sessions. Patients rated the intensity, quality and frequency of
their phantom limb pain before each treatment session, as well as
how much the pain intruded on sleep and activities of daily living.
Once they completed all 12 sessions they had follow-up interviews
one, three and six months after treatment.
By the end of these sessions, participants reported an average 50
percent reduction in pain intensity, duration, quality and frequency
– and these improvements remained after six months, Ortiz Catalan
said. They also had about a 50 percent decline in the intrusion of
pain on their sleep and day-to-day activities.
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All of the patients said they felt constant pain at the start of the
study, but by six months only half of them did. Stabbing, tiring or
exhausting pains in the phantom limb were also less common after
treatment, the study found.
Beyond its small size, the short duration of the treatment and
follow-up period is a limitation of the study, the authors note. The
trial also didn’t include a control group of patients who didn’t
receive treatment so it’s possible the pain reduction people
reported after the sessions might be a placebo effect, the
researchers point out.
This virtual reality game wouldn’t work for patients with nerve
injuries or people who can’t move their stump.
There are few effective treatments for phantom limb pain. Surgery
and drug treatments only provide limited pain relief while creating
side effects. An intervention known as mirror therapy that uses
reflections of the unaffected limb to make it look like the patient
is moving their missing limb sometimes helps.
“Mirror therapy is beneficial for many people, and is obviously much
more accessible and cheaper than the high tech solution described in
this study, but the therapy needs to be continued over time to
maintain benefits,” said Dr. Melita Giummarra, a researcher at
Monash University in Australia who wrote an accompanying editorial.
“Given this knowledge, I wonder whether the effects of this virtual
reality model would be maintained over time without access to the
system for booster therapy,” Giummarra told Reuters Health by email.
SOURCE: http://bit.ly/2guc1xG and http://bit.ly/2gf6x61 The Lancet,
online December 1, 2016.
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