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New Ideas About Nervous System Function in Complex Regional Pain Syndrome
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Posted on: 11/30/1999
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This group of researchers have been studying patients with complex regional pain syndrome (CRPS) for a long time. They've been trying to figure out what causes the symptoms these patients suffer in order to find better ways to treat CRPS (or even prevent it).
Complex regional pain syndrome (CRPS) is a group of symptoms usually affecting the arm and hand on one side but it can affect the leg and foot (and even other parts of the body). After trauma, injury, or surgery, the person develops pain and changes in skin temperature and circulation to the affected area(s). The involved body part can become very cold and clammy or very hot and sweaty. Patches of dark hair might form on the back of the hand or forearm. The pain that accompanies CRPS can be very excruciating.
Scientists think the changes that occur develop because normal function of the sympathetic nervous system (SNS) has been interrupted or disrupted. The automatic portion of the nervous system that keeps you breathing and your heart beating is broken down into two parts: the parasympathetic and the sympathetic nervous systems.
The sympathetic nervous system is the get up and go guy. This part of the nervous system makes sure you can run fast and jump high when being chased by a tiger (or during any stressful situation). The sympathetic nervous system is balanced by the parasympathetic nervous system (PNS).
The parasympathetic nervous system is the rest and digest part of the automatic nervous system. It's the parasympathetic nervous system that brings calm and order back into balance after any kind of stress (physical, mental, emotional). It helps bring your pulse and blood pressure back down, relaxes your muscles, and turns your bowel and bladder functions back on.
Previous studies have shown that some people with complex regional pain syndrome eventually get better. Their nervous systems seem to recover and return to normal functioning. Others end up with a permanent set of changes that reduce their hand function for the rest of their lives.
In this study, the authors take a look at the status of the sympathetic nervous system over time in patients with a diagnosis of upper extremity complex regional pain syndrome (CRPS). Using the Michigan Hand Outcome Questionnaire (a measure of pain and hand function) and a Doppler study (measure of skin blood-flow), the scientists compared early to late results. Subjects in the study all had CRPS for at least three years before becoming a part of this study. Men and women adults were both included.
As part of the tests of sympathetic nervous system responses, skin blood-flow was measured in both hands under two separate conditions. In the first one, skin blood flow was monitored as the patient took a deep breath in and let it out fully. During the second provocative test (meant to provoke the sympathetic nervous system into responding), an ice pack was applied to the uninjured upper arm. Skin blood-flow was measured continuously as the cold pack was put on and taken off (looking for a normal response to the cold and return to normal).
Results were compared to values measured in normal adults of the same ages. They found pathologic results in response to both tests -- and in both hands! That means the uninjured hand also showed some deterioration of the sympathetic nervous system function, too.
The most interesting result was that hand function was no different between patients who had complex regional pain syndrome (CRPS) plus sympathetic nervous system impairment and those patients who only had CRPS (without sympathetic nervous system dysregulation). Hand function refers to activities of daily living, pain, and work performance. But it also includes the patient's perception of appearance, and overall patient satisfaction.
They also found that some people developed greater impairments of the sympathetic nervous system function over time. Half of the patients who tested with normal nervous system function at first later developed measurable sympathetic nervous system dysfunction.
The reason for the lack of sympathetic nervous system recovery in some CRPS patients and the deterioration in others has not been explained. The fact that function isn't always affected by changes in sympathetic nervous system function may be because there is some other (as yet unknown) factor at work here.
The authors propose the theory that people with CRPS who lose their automatic nervous system reflex responses might have a faulty nervous system to begin with. It's possible that's why they develop complex regional pain syndrome after trauma when others with similar injuries recover normally. One way to find out is to measure the sympathetic nervous system function in many normal, healthy adults and follow them their whole lives to see who develops CRPS. That's a major undertaking but could be done in conjunction with other lifelong studies already underway.
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References:
Tobias Vogel, MD, et al. Sympathetic Dysfunction in Long-Term Complex Regional Pain Syndrome. In The Clinical Journal of Pain. February 2010. Vol. 26. No. 2. Pp. 128-131.
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