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.
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.