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.4
