Ease pain by taking a good look at yourself
13:10 01 November 2005
NewScientist.com news service
Gaia Vince

Some patients suffering chronic pain in their limbs have found an unlikely source of relief – mirrors. Researchers say the drug-free treatment works on people with complex regional pain syndrome (CRPS) and repetitive strain injury (RSI) because it tricks the brain into correcting its distorted image of the body.

CRPS occurs in about one-third of people who fracture their wrists: they suffer unexplained persistent pain in their hand, arm or shoulder once the supportive plaster cast is removed. The pain can be so bad that some patients beg for their arm to be amputated, says Candy McCabe, who developed the novel mirror therapy at the University of Bath in the UK.

In the study, eight CRPS patients sat in front long mirrors. These were placed so that each person could see only the healthy half of their body, along with another reflection of the same half.

The result was that the side of the body with the painful arm was hidden from their view and it appeared to the patients as if they had two healthy arms. They were told to concentrate hard on the image and try to believe that what they saw was a true depiction of themselves.

“Three of them were cured instantly; the others took a little longer,” says McCabe. “But once the mirror was removed, the pain returned.” However, with continued mirror therapy, six people were completely cured. The two exceptions had conditions complicated by limb ulcers and actual physical distortions.

Refined body image

Since the experiment, McCabe says she has successfully treated many other CRPS, and RSI patients, with the technique. She believes the pain results from a mismatch in the way the brain perceives the body and the actual condition of the body.

The brain is constantly sending signals to the body, predicting things like the shape and weight of the limbs, and their location. The sensory nervous system responds by sending information back, allowing the brain to refine its body image.

“When the arm is immovable in a plaster cast a mismatch occurs," McCabe says. "The brain sends out signals to the arm, but gets nothing back, so it triggers its own pain sensation in response." When the cast is removed, most people recover from the confusion spontaneously, but a third continue to feel pain. "The mirror tricks the brain into resetting its body image and stops the pain,” she says.

She thinks a similar mismatch occurs in people who develop RSI. "When a typist stares at a still screen, or a violinist at sheet music, while their hands move rapidly, it causes confusion,” McCabe says.

Mild tingling

In a further study to test their brain mismatch theory, McCabe and colleagues at Bath Royal National Hospital for Rheumatic Diseases conducted an experiment on 41 healthy volunteers. As before, each was sat in front of a mirror which bisected them in two, giving them a symmetrical image of their body, and were asked to believe that the image truly represented them.
They were asked to move their two arms in different directions while watching their reflection – creating a mismatch between the actual motion of the hidden arm and the apparent motion viewed in the mirror.

“Almost instantly they began to feel sensations in the arm they couldn’t see, which ranged from mild tingling through to uncomfortable levels of pain, McCabe said. “Some found it too painful to last the 20-second test duration.”

Peter Buckle, an RSI expert at Robens Centre for Health Ergonomics at Surrey University, says it is well-known that the brain can be confused by creating a difference between actual and apparent motion. But he does not believe this is a factor in RSI. “RSI has been around for hundreds of years and describes very real physical symptoms including inflammation and nerve damage," he says.