Something New About Complex Regional Pain Syndrome


Patients with complex regional pain syndrome (CRPS) are faced with some very unpleasant symptoms. The first is unrelenting burning or aching pain followed by skin sensitivity, swelling, discoloration, sweating, and temperature changes.

The most commonly affected area of the body is the hand or foot, but the symptoms can spread further up the affected limb and even into the opposite limb. If the condition becomes chronic, dystrophy or deterioration of the bones and muscles in the affected body part may occur.

CRPS doesn’t just come on without a reason. Usually there’s been an injury as minor as having blood drawn or a sprained ankle. Other times, it may be the result of a more significant injury such as surgery, a fracture, immobilization with casting or splinting, or the result of a stroke.

Many patients have such a distorted sense of where the affected arm is that they wish the arm could be cut off and be done with it. Imagine not knowing where your arm is even when you are touching something with that hand. Now imagine trying to use your keys to open a door, using your fingers to pick up a pen, or even using your hand to wipe yourself after going to the bathroom but you don’t know where that arm is.

That’s the sensation many people with complex regional pain syndrome (CRPS) experience everyday. Therapists working with these patients refer to this phenomenon as a distortion of body image or distortion of body schema. The failure to recognize limb position is a problem with position accuracy.

In this study, efforts are made to measure upper limb (arm) position accuracy in patients with CRPS of one arm. Movements of the arm were videotaped and compared against movement in the healthy arm and arm movement in volunteers who did not have CRPS. Patients were matched by age and sex (males and females) with the normal, healthy volunteers (control group).

Everyone moved the arm through a set pattern of motions based on the position of numbers on a horizontal clock. Twelve o’clock was straight out in front of the person seated in a quiet room. Three o’clock was out to the right side. Nine o’clock was out to the left side and so on.

The individuals moved the arm (or attempted to move the arm) to various times randomly selected by a computer. Each person completed six sets of arm positions based on clock hour positions. Half the trials were done using vision, while the other half was done wearing glasses that prevented the person from seeing the arm. The idea was to measure how much vision affects movement in patients with complex regional pain syndrome (CRPS).

The movements were captured on film by a camera stationed above the person being tested. Video analysis software was used to make judgments about the arm movements and provide data on how far off each actual arm movement was from the intended target.

In other words, if the patient/subject was supposed to point to three o’clock, how far away from that point did the arm go? The difference in degrees between the correct arm position and the actual arm position was the main measure of arm position accuracy. Arm pain and perceived level of difficulty in awareness were also measured using rating scales. There were several important findings from this study:

  • Limb position accuracy was distorted in both arms (affected and unaffected) of the patients
    with complex regional pain syndrome (CRPS). This suggests a problem with general awareness of limb position.

  • All but one patient in the CRPS group had a mental picture of the affected arm that
    included some distortion. For example, part of the arm was missing altogether or a finger was oddly shaped. Some patients described the arm as much larger than it actually was.

  • Having pain anywhere in the affected arm did not help them find the arm. Being able to see
    the arm did help.

    The authors suggested that since limb position awareness was challenged in both arms when only one arm had CRPS points to the possibility of what is called central processing errors. Central processing refers to the natural function of the nervous system (nerves, spinal cord, brain).

    In the case of CRPS, errors occur in the nervous system’s ability to keep track of all body parts at any given time. Vision helps keep the nervous system up-to-date on just where that arm really is at any point in time. Factors other than vision may come into play but for the moment, this is only a theory. What those other factors may be remains unknown at this time.

    How does this new information help in the treatment of patients with complex regional pain syndrome (CRPS)? First, knowing that vision is an important feedback mechanism may help therapists use visual input and visual cues when working on limb position accuracy. Visual feedback may also help improve the brain’s mental representation of the arm. Improving the accuracy of reaching and grasping function can go a long way in avoiding accidents and injuries.

    Second, experts working in the area of motor control and motor dysfunction may be able to find ways to improve function. Discoveries made with other problems that involve distortion of central processing of sensory and motor input may work with complex regional pain syndrome.

    And third, this first insight into impaired limb position accuracy in patients with complex regional pain syndrome has opened the door to further study of the problem. Scientists can begin to look for the exact neural processing pathways that are affected by CRPS and perhaps find ways to restore normal sensorimotor function.