Individuals with complex regional pain syndrome experience pain simply by watching other people's movements. Breaking research, carried out by Aalto University in Finland, uncovers the neurological changes behind this phenomenon.
Complex regional pain syndrome (CRPS) is characterized by long periods of excessive pain, changes in skin color, temperature, and swelling.
Although the condition can normally be traced to an injury in the area, the reason why it develops after some injuries but not others is not understood.
The pain associated with CRPS is reported to feel like someone is crushing or squeezing the affected limb.
In some cases, the pain can even transfer to the opposite limb, and only the lightest touch can trigger intense pain.
The appearance of the skin can change, too; skin color can fluctuate between blue, purple, red, and pale, and it can also appear shiny and thin. Sweating patterns in the region may be altered and nail and hair growth patterns can change.
Alterations in the control of microcirculation are thought to cause the changes in skin color and intermittent swelling.
Differentiating characteristics of CRPS
There are other characteristics of CRPS that set it apart from other pain conditions. For instance, if a patient's view of their limb is magnified, the pain and swelling intensify, and, conversely, if their view of the limb is minified, the pain and swelling subsides.
Also, if the patient cannot see their limb, performance of simple motor tasks is significantly impaired. The condition is clearly complex and involves both central and peripheral nervous systems.
CRPS can occur in anyone at any age, although it is more common in women; it rarely occurs in children under 10 and the average age of onset is 40.
Many individuals will recover over time, but some do not recover at all and the condition can be debilitating.
Although 90 percent of CRPS cases are preceded by an injury, it is not clear why only certain people develop the condition. The most common triggers are fractures, limb immobilization (for instance, being in a cast), sprains and strains, soft tissue injury (such as cuts, bruises, or burns), or surgical procedures.
CRPS and motor function
In addition to the physical symptoms, CRPS often comes with abnormalities in central motor function and perception; pain is intensified when an individual moves. Strangely, the pain also worsens as they watch others carry out motor activities. In other words, the simple act of watching someone making a movement can increase their pain levels.
The investigators from Aalto University set out to explore the neurological signals that underpin this interesting phenomenon. Their results were published this week in Journal of Pain.
The study involved 13 individuals with upper-limb CRPS (all females, aged 31-58) and 13 healthy control subjects, matched by sex and age. They analyzed functional magnetic resonance images (fMRI) taken as the participants watched videos of movements - for instance, a hand squeezing a ball with maximum force.
As these actions were observed, brain scans from individuals with CRPS showed abnormal patterns in certain brain areas compared with the controls.
In particular, the following brain regions reacted significantly differently between the two groups:
- Hand representation area in the sensorimotor cortex - the part of the brain that deals with motor and sensory information for that particular part of the body
- Inferior frontal gyrus - used when observing actions
- Secondary somatosensory cortex - normally activates in response to pain, light touch, visceral sensation, and when focusing on a particular tactile sensation
- Inferior parietal lobule - involved in interpreting sensory information
- Orbitofrontal cortex - thought to be involved in sensory integration and pain modulation
- Thalamus - processes and relays most sensory information as it enters the body.
The authors conclude: "Our findings indicate that CRPS impairs action observation by affecting brain areas related to pain processing and motor control."
Although this discovery is just a small step along the way to understanding CRPS, because so little is known about the condition, all information we can gleam is vital.
"Our discovery may help to develop diagnostics and therapeutic strategies for CRPS patients."
Study co-author Jaakko Hotta
The researchers are quick to mention that their sample size was small and that more than two thirds of the group were taking opioid painkillers; they are eager for further work to be carried out. However, shortfalls aside, the findings add an interesting insight into the mysterious condition.
Currently, treatment options for CRPS are limited. Research in this vein may eventually help to design useful drugs of the future.