An Overview of CRPS
The name CRPS is not important; it will probably change, not any time soon, but eventually. CRPS is still commonly known as reflex sympathetic dystrophy. People who suffer from the disease often refer to themselves as RSD’ers.1 Clinicians and scientists who study CRPS are persuaded to think that it is a neuro-immune disease whose pathophysiology we will eventually understand. Until such a time, CRPS remains a collection of symptoms and signs that most clinicians will encounter during the course of their practice. Be not deceived, most us will probably have missed, and will miss again, the diagnosis on first encounter with a patient suffering with CRPS.
"CRPS obtains an intensity of pain and disability that is shared by few neuropathic pain disorders. The hallmark symptom of CRPS is pain that is out of proportion to its apparent inciting cause."
The Irony of CRPS
The peculiar nature of CRPS makes it the object of intense study and also, for some, the object of skepticism and derision. CRPS obtains an intensity of pain and disability that is shared by few neuropathic pain disorders. The hallmark symptom of CRPS is pain that is out of proportion to its apparent inciting cause. Colles’ fractures and ankle sprains are common antecedent events. They usually heal within a predictable and reasonably short period of time. Surgical wounds that heal without infection shouldn’t cause prolonged, severe pain. It doesn’t make sense that they should be followed by pain of such severity that the experience of it represents not only a medical crisis, but also an existential and, often, a spiritual crisis. The "reality" of CRPS is counter-intuitive.
It has been said of an unrelated disease, myositis ossificans progressiva—as it has of other conditions—that "more people study the disease than have it." In that particular case it is because the disease illuminates the normal mechanism and the genetic variation of the ossification of skeletal tissues. It therefore attracts great scientific interest even though it is exceedingly rare. Similarly, the study of CRPS has much to say about the normal regulation of nociception and the experience of pain. Tragically, many more people have CRPS than study it. In the Netherlands, the TREND (Trauma RElated Neural Dysfunction) Consortium has registered 8,000 people with the confirmed diagnosis of CRPS 2 and there is an estimated incidence of 26.2 per 100,000 patient years.3 The population of the Netherlands is 16 million, making the incidence of new "cases" of CRPS greater than 4,000 per year. The prevalence of registered patients may underestimate the true prevalence of CRPS by 50%. With a population of 300 million, the United States may have between 150,000 and 250,000 people suffering with CRPS.
Comparison between the United States and the Netherlands is instructive in another sense. With a landmass of 33,900 square kilometers, Holland has a population density of 485 people per square kilometer, one of the highest in the world. The population density of the United states is 31 persons per square kilometer over a land mass of more than 9 ½ million square kilometers. My point is that the Netherlands is able to provide a series of dedicated CRPS treatment centers from Maastricht in the south, through Rotterdam, Leiden and Amsterdam, to Groningen in the north. For most Netherlanders, a CRPS treatment center is within a reasonable distance by a reasonably-priced train ride. That is not to say there are not excellent CRPS centers in the United States. There are many, but they are too few and too far between.
Pain practitioners across North America, at one time or another during their careers, consult with their orthopaedic, neurosurgical, physiatry, neurology, anesthesiology and medical colleagues in the care of people with CRPS. They will assume responsibility for care that might ideally take place in a center that is capable of implementing diagnostic and treatment protocols in a controlled environment and using controlled methodology with well-validated outcome measures. What is ideal is not always practical.
The characterization of CRPS is incomplete. Although there are a number of excellent reports on the natural history and patterns of symptoms and signs in people with CRPS, a taxonomy of the types and sorts of the condition based on the predominant mechanisms of disease is not yet possible. RSD’ers intuitively know that their CRPS has widespread and long-lasting effects on their long term health and wellness. There may be chronic organ system impairments, perceptual impairments and even cognitive impairments that are as yet unstudied. Recently, the not-for-profit Reflex Sympathetic Dystrophy Syndrome Association,4 with the funding support of the Brodsky Family Foundation, has launched a 20-year, Internet-based, longitudinal study of the natural history and collateral health effects of CRPS.5 The first 2-year interim report should be ready for public disclosure in 2012.
Diagnostic Criteria for CRPS
The International Association for the Study of Pain (IASP) developed diagnostic criteria for CRPS in 1994 6,7 and modified them at its Budapest conference in 2004.8 The diagnostic criteria are under continuous review to improve their specificity while maintaining adequate sensitivity.9 The clinician is inclined to make the diagnosis more easily and begin treatment early for some patients who may not have CRPS (using diagnostic criteria that are sensitive but not very specific), rather than miss the diagnosis and permit CRPS to progress in intensity as well as duration (using criteria that are specific but not sensitive enough). Table 1 presents the current IASP diagnostic criteria for CRPS. The "clinical criteria" are more sensitive while the "research criteria" are more specific.