People suffering from chronic pain often find their condition distracting and debilitating, but new research reveals that some might in fact be paying less, rather than more, attention to the source of their pain (University of Bath, 2017).

The findings from researchers at the University of Bath and the University of Oxford, published in BRAIN, suggest that complex regional pain syndrome (CRPS), a rare chronic pain condition might involve changes in the way that the brain processes visual information, which in turn could provide new insights into how to treat the condition.

Approximately 16,000 people in the UK are affected by CRPS, which is a poorly understood condition. Individuals with CRPS report debilitating pain in an arm or leg, as well as swelling, temperature changes and movement difficulties. Symptoms include burning, stabbing, stinging or throbbing pain in the affected limb, and everyday sensations such as a breeze blowing across the skin can feel very painful.

Whilst its exact causes are not yet known, it is thought that abnormal brain signals about the limb play an important part. CRPS usually follows limb damage from injury or surgery, but the pain experienced is disproportionate and may last longer than would be expected for the damage itself. For one case in every ten there is no obvious trigger. And whereas most people recover well within a year, some people have some or all of the symptoms for many weeks, months or even years.

For their study, the scientists were keen to understand more about how and why individuals suffering from CRPS report losing track of the position of their painful limb and not being able to move it. The team tested how quickly people with CRPS processed visual information in the side of their environment nearer to their painful limb compared to the other side of the environment. Using laser pointers controlled by a computer, they projected two flashes of light onto the left and right side of a board that was placed in front of the patients, and the patients had to say which light appeared first.

Their results showed that people with CRPS processed the light on the affected side of the board more slowly than the light on the unaffected side, suggesting that information that is nearer to the affected side of the body is not well processed by the brain.

Lead author, Dr Janet Bultitude from the University of Bath’s Department of Psychology and Centre for Pain Research, said “People with CRPS are usually in constant pain that they can’t ignore. Yet paradoxically they often report that they are not sure where their painful limb is unless they look at it directly, and that movements are not automatic – they have to ‘tell’ their limb to move. The odd sensations they experience suggest there could be a change in mechanisms that normally allow us to process information at different locations in the space around us. Our results show that people with CRPS are slower to process visual information that comes from the side of their environment where their painful limb is normally located. Since we used a test of vision, the slower processing can’t be because of changes in the limb itself, but must be due to the way the brain processes information. We’re excited that these results can help propel us forward to developing new treatments for those affected by the condition.”

Current treatments for CRPS include pain medications and rehabilitation therapies which are vital to normalise sensation in the limb and improve function and mobility. Janet Bultitude and her team are now investigating whether symptoms of CRPS could be reduced by therapies that are used to treat attention problems in people with brain injuries such as stroke.

To be eligible to take part in the study participants must live in the UK, be 18-80 years of age, and have CRPS that has predominantly affected one upper limb for at least three months (University of Bath, 2017). People who have had a stroke or other brain injury cannot take part in the study.

The researchers are conducting a double-blind, randomised, sham-controlled trial of sensorimotor training. Both the real and control treatment will take place in the participant’s own home and will involve performing simple movements with their affected arm while wearing glasses that distort vision. Participants will be required to travel to one of the research centres in Bath, Oxford, or Exeter four times over an eleven week period. It might also be possible for the researchers to come and see participants at home. They will examine the participant’s symptoms in person and also through questionnaires that will be sent by post. In addition to testing a new potential treatment for CRPS, this study will help gain insights into the symptoms that people with CRPS experience.

Janet Bultitude said “This is an exciting opportunity to help us test a brand new treatment option for CRPS. Sensorimotor training takes only a few minutes a day, is inexpensive, and can be performed in the home. Preliminary research on the treatment has had promising results, and we want people to come forward to help us test its effectiveness in a larger, more controlled study. We hope that the results will lead to the development of sensorimotor training for use in CRPS treatment.”