Complex Regional Pain Syndrome
By Steven A. King, MD, MS, Psychiatric Times
URL:
http://www.psychiatrictimes.com/article/showArticle.jhtml?articleId=189500108

June 2006, Vol. XXIII, No. 7


Of all the common pain syndromes, perhaps none is so misunderstood by both
physicians and patients as complex regional pain syndrome (CRPS). Types I and
II of CRPS are the current names for what were previously called reflex
sympathetic dystrophy (RSD) and causalgia, respectively. Because of limited
knowledge about these disorders, patients who suffer what is frequently very
severe
pain often have their condition misdiagnosed and do not receive appropriate
treatment.

Although many physicians are still relatively unfamiliar with these
disorders, the first in-depth description was made over 140 years ago by the
physician often considered the father of American neurology, S. Weir Mitchell,
and
his colleagues, based on their observations of soldiers wounded in the Civil
War. They noted that some soldiers who were wounded in the hand or foot
developed a burning pain that was exacerbated by touching the affected body
part.
This syndrome was named causalgia, Greek for “burning pain.”

Multiple similar conditions were described over the years and received a
variety of names, including post-traumatic injuries, algodystrophy, and Sudeck
atrophy. In 1953, John Bonica, one of the pioneers in the study of pain,
suggested that these disorders be subsumed under “reflex sympathetic
dystrophy.”
However, the validity of this term has been questioned frequently. One of the
major problems encountered in its use is the uncertainty of the role of the
sympathetic nervous system (SNS) in this disorder. The fact that there is a
great deal of variability in response to sympathetic blocks suggests that in
many patients, the pain is not due to a disorder of the SNS.

Because of this and the general confusion over RSD and causalgia, the
International Association for the Study of Pain renamed these syndromes in its
classification of chronic pain.1 RSD became CRPS type I and causalgia became
CRPS
type II. The diagnostic criteria for CRPS are shown in the Table (see June
2006 Psychiatric Times, page 9). The difference between types I and II is that
in the latter, there is evidence of a definable nerve lesion.

Two terms used to describe the pain, allodynia and hyperalgesia, are notable
in the criteria for both types of CRPS. Allodynia is pain due to a stimulus
that is not usually painful and is commonly the most dramatic presenting
symptom of these disorders. Patients with this problem may wear loose-fitting
clothing to limit the amount of contact between it and the skin in the affected
area. In more severe cases, patients may complain that even having bedsheets
touching the body part can cause severe pain. In hyperalgesia, a normally
painful stimulus causes more discomfort than expected. Both allodynia and
hyperalgesia are covered by the more general term “hyperesthesia,” an
increased
sensitivity to stimulation.

The frequency of occurrence of CRPS is unclear. A recent study of patients
with fractures of the distal radius reported that CRPS type I developed in
18%.2 Another study of 162 soldiers wounded in the Iraqi war who were seen in
pain clinics reported that 4.3% suffered CRPS type II and 1.9%, CRPS type I.3
Based on reports that patients with CRPS often see a number of physicians
before their condition is diagnosed correctly, it appears that many cases are
never diagnosed. Type I may especially go unrecognized because of the absence
of
an identifiable peripheral nerve injury and the usual relationship of the
disorder to some form of trauma, ranging from an accident-induced injury to
surgery or diseases that can cause pain, including myocardial infarction and
post-herpetic neuralgia. Since pain is an expected sequela of these events, the
possibility of CRPS may not be considered by health care providers for lengthy
periods.

Unfortunately, because many patients with CRPS appear “normal” and because
pain such as allodynia seems so bizarre and so foreign to most laypeople and
even some health care professionals, patients may be mistakenly thought to be
either exaggerating their pain for secondary gain or even malingering. One of
the saddest things is that these patients may find their pain discounted by
so many others and may be stigmatized as falsifying their discomfort.

The cause of CRPS remains a mystery. A variety of physiologic mechanisms
have been proposed. The classic view that the pain is due to hyperactivity of
the SNS has been discounted, although the SNS appears to be involved in some of
the symptoms, most notably the edema, blood flow, and sudomotor changes.
Currently, CRPS is believed to be due to a combination of peripheral and
central
factors.4 Among the peripheral mechanisms that have been proposed are an
inflammatory process, peripheral sensitization, and changes in sodium channels.
These processes may result in central changes, including an exaggerated
response to the peripheral input and a reduction of descending inhibitory
pathways.

Because the severity of the original trauma does not appear to be correlated
with these disorders, the significance of psychological factors and the
possibility that they may play an important role—if not the major role—in
the
development of the pain have often been the focus of attention. Despite this
speculation, there have never been consistent findings of a correlation between
preexisting mental disorders and the development of CRPS. However, it has
been proposed that there may be changes in the brain, most notably in the
primary sensory cortex, secondary to CRPS, and that these can lead to a
distorted
body image.5,6 What role these changes may play in the pain and other symptoms
of CRPS is still the subject of speculation.

In my next column, I will address the diagnostic workup and treatment of
CRPS.

Dr King is clinical professor of psychiatry at the New York University
School of Medicine.

References
1. Merskey H, Bogduk N, eds.Classification of Chronic Pain: Descriptions of
Chronic Pain Syndromes and Definitions of Pain Terms. 2nd ed. Seattle: IASP
Press; 1994.
2. Puchalski P, Zyluk A. Complex regional pain syndrome type 1 after
fractures of the distal radius: a prospective study of the role of
psychological
factors. J Hand Surg (Br). 2005;30:574-580.
3. Cohen SP, Griffith S, Larkin TM, et al. Presentation, diagnoses,
mechanisms of injury, and treatment of soldiers injured in Operation Iraqi
Freedom:
an epidemiological study conducted At two military pain management centers.
Anesth Analg. 2005; 101:1098-1103.
4. McBride A, Atkins R. Complex regional pain syndrome. Curr Orthop.
2005;19:155-165.
5. Moseley GL. Distorted body image in complex regional pain syndrome.
Neurology. 2005;65:773.
6. Birklein F, Rowbotham MC. Does pain change the brain? Neurology.
2005;65:666-667.





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