History
The most widely accepted criteria for the diagnosis of complex regional pain syndrome (CRPS) were published by the International Association for the Study of Pain (IASP). It lists the diagnostic criteria for CRPS I as follows: [26, 27]
The presence of an initiating noxious event or a cause of immobilization
Continuing pain, allodynia (perception of pain from a nonpainful stimulus), or hyperalgesia disproportionate to the inciting event
Evidence at some time of edema, changes in skin blood flow, or abnormal sudomotor activity in the area of pain
The diagnosis is excluded by the existence of any condition that would otherwise account for the degree of pain and dysfunction.
According to the IASP, CRPS II (also known as causalgia) is diagnosed as follows:
The presence of continuing pain, allodynia, or hyperalgesia after a nerve injury, not necessarily limited to the distribution of the injured nerve
Evidence at some time of edema, changes in skin blood flow, or abnormal sudomotor activity in the region of pain
The diagnosis is excluded by the existence of any condition that would otherwise account for the degree of pain and dysfunction.
The IASP CRPS Special Interest Group conducted a review in 2019 to evaluate ambiguities and diagnostic pitfalls of the criteria. The group was able to update assessment instructions without text alterations to maintain the validity of the IASP criteria. The outcome was the addition of four additional requirements as follows: [14]
A. The patient has continuing pain which is disproportionate to any inciting event
B. The patient reports at least one symptom in 3 or more of the categories
C. The patient displays at least one sign in 2 or more of the categories
D. No other diagnosis can better explain the signs and symptoms
The major difference between the original IASP criteria and the updates is that the above-listed criteria must be met to diagnose CRPS. Validation of the criteria was proposed by Harden et al in 2010 secondary to high sensitivity and lower specificity, leading to overdiagnosis of false-positive cases for CRPS. [28] The above criteria is summarized into a table below.
Updated IASP diagnostic guidelines for CRPS.
While the IASP has published and updated their guidelines, others have developed a slightly different methodology to include follow-up metrics. Brunner et al performed a Delphi survey among international experts. [29] The survey asked those experts to list and grade diagnostic and follow-up parameters for CRPS I. Although there was some disagreement about weighting, the consensus follows.
The three diagnostic parameters, each with a subcategory, are listed below.
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Pain
Hyperesthesia
Hyperalgesia
Allodynia
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Signs
Edema
Color
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Mobility
Motor change
Range of motion
Strength
The one follow-up parameter is clinical course. The subcategories are as follows:
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Decrease in pain
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Decrease in hyperalgesia
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Decreased edema
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Improvement in motor function
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Improvement in strength
The expert consensus was that the diagnosis can and should be established without additional studies (radiography, scintigraphy). [29] Other authors believe likewise. [30] Much of the older CRPS literature notes a predisposing personality of depression. However, many other studies have demonstrated that, while most patients are depressed, they are depressed because of their pain. (See causes below.)
Many patients with CRPS will exhibit some type of movement disorder ranging from strength reduction (78%) to tremor (25-60%) to myoclonus and dystonia. Although some authors believe these are pain-induced findings, others believe they are primary abnormalities. [31]
Physical
The physical findings for complex regional pain syndrome (CRPS) have been listed as part of the "History" section because the criteria sets include both signs and symptoms. Three stages have been classified. Although a consensus panel recommended that staging be eliminated, it is important that the emergency physician has an awareness of potential disease progress. Disease progress is very variable.
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Stage I or early CRPS: Pain is more severe than would be expected from the injury, and it has a burning or aching quality. It may be increased by dependency of the limb, physical contact, or emotional upset. The affected area becomes edematous, may be hyperthermic or hypothermic, and shows increased nail and hair growth. Radiographs may show early bony changes. Duration is usually 3 months from onset of symptoms. Some patients remain in one stage or another for many months or even years. They may never progress or they may progress quickly to late stage. Remember that physical findings may be minimal, especially in those who remain in stage I or progress slowly.
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Stage II or established CRPS: Edematous tissue becomes indurated. Skin becomes cool and hyperhidrotic with livedo reticularis or cyanosis. Hair may be lost, and nails become ridged, cracked, and brittle. Hand dryness becomes prominent, and atrophy of skin and subcutaneous tissues becomes noticeable. Pain remains the dominant feature. It usually is constant and is increased by any stimulus to the affected area. Stiffness develops at this stage. Radiographs may show diffuse osteoporosis. The 3-phase bone scan is usually positive. Duration is 3-12 months from onset.
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Stage III or late CRPS: Pain spreads proximally. Although it may diminish in intensity, pain remains a prominent feature. Flare-ups may occur spontaneously. Irreversible tissue damage occurs. Skin is thin and shiny. Edema is absent. Contractures may occur. Radiographs indicate marked demineralization.
Extensive changes are present in the muscles of patients with long-standing disease. [32]
Causes
Many hypotheses exist, but a definite cause for complex regional pain syndrome (CRPS) has not been identified. The most frequently associated inciting events that lead to a diagnosis include trauma, extremity fractures, surgery, and carpal tunnel syndrome.
Older literature suggested that development of CRPS required a triad of conditions: an injury, an abnormal sympathetic response, and a predisposing personality. Most current literature disputes the need for an underlying personality disorder. In August 2000, Schwartzman stated, "There is no evidence that affected patients have a personality disorder, but the severity of pain and the disruption of the patient's life can lead to anxiety and depression." [33] Beerthuizen et al reviewed 31 articles that addressed an association between psychiatric illness and CRPS-1. Almost all the studies showed no causal relationship. [34]
Peterlin et al suggested that migraine may be a risk factor for the development of CRPS, but this is the only paper suggesting an association. [35]
ACE inhibitors have been suggested as a possible cause for the development of CRPS. [15, 36]
Evidence now shows that CRPS may have a genetic predisposition. [10, 11]
Complications
Once refractory to neural blockade, pain is probably lifelong and may be severe enough to be debilitating.
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Updated IASP diagnostic guidelines for CRPS.
