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Complex Regional Pain Syndromes

Background

In 1994, a consensus group of pain medicine experts gathered by the International Association for the Study of Pain (IASP) agreed on diagnostic criteria for reflex sympathetic dystrophy (RSD) and causalgia, and renamed them complex regional pain syndrome (CRPS) types I and II, respectively. These designations were determined by the type of inciting event, rather than by any differences in clinical presentation or pathophysiology. Many experts felt that the IASP diagnostic criteria were ambiguous; however, these criteria were developed as just a starting point, and the IASP fully intended to validate them through clinical research studies.

CRPS type I requirements feature causation by an initiating noxious event, such as a crush or soft tissue injury; or by immobilization, such as a tight cast or frozen shoulder. CRPS type II is characterized by the presence of a defined nerve injury. Both types demonstrate continuing pain, allodynia, or hyperalgesia that is usually disproportionate to the inciting event. At some point during the syndrome’s development, both show evidence of edema, changes in skin blood flow revealed by color changes and skin temperature changes greater than 1.1°C from the homologous body part, or abnormal sudomotor activity in the painful region. Both types require the exclusion of any other condition that might account for the degree of pain and dysfunction seen.

The 1994 IASP criteria have proven to be extremely sensitive (ie, they rarely miss a true case of CRPS). However, since their inception, the 1994 taxonomy has been criticized by experts on clinical criteria validation and specialists in pain medicine on the grounds that the criteria are insufficiently specific (ie, use of the criteria results in overdiagnosis of CRPS). A small single center validation study demonstrated empirically that the 1994 CRPS criteria did indeed cause overdiagnosis of the syndrome.

In response to such concerns, investigators used factor analysis to categorize 123 patients with CRPS into 4 statistically distinct subgroups.
This resulted in modified diagnostic criteria felt to be valuable for further validation studies.

In 2003, a closed workshop was held in Budapest, Hungary to study and resolve this matter. Experts in CRPS published the results of this workshop in a 2007 review article
showing that the modified criteria, mentioned above, produced better discrimination between CRPS and non-CRPS neuropathic pain, yielding better diagnostic accuracy than the original unmodified criteria.

The study results indicated that when 2 of 4 sign categories were present and 3 of 4 symptom categories were present, the resultant sensitivity was 0.85 and the specificity was 0.69 for a clinical diagnosis of CRPS. This appeared to be a good compromise between identifying as many patients as possible in the clinical context and substantially reducing the high level of false-positive diagnoses associated with the 1994 IASP criteria. However, a higher specificity is required to meet research criteria, so the committee recommended that 2 of the 4 sign categories and all 4 symptom categories must be positive for the diagnosis to be made in a research setting, resulting in a sensitivity of 0.70 and specificity of 0.94.

Due to the combination of increased specificity and reduced sensitivity, about 15% of patients previously diagnosed with CRPS were considered “without a diagnosis.” Therefore, a third diagnostic subtype, complex regional pain syndrome not otherwise specified (CRPS-NOS), was recommended to categorize those patients.
These new IASP diagnostic criteria have been submitted to the medical committee for Classification of Chronic Pain of the IASP for future revision of formal taxonomy and diagnostic criteria. 

The criteria are given here in hopes that higher specificity for the identification of CRPS will enhance research into the pathoetiology of this disorder without creating a reduced, or even harmful, rate of clinical diagnosis that could deny affected patients access to treatment. In addition, these criteria may result in more cost-effective approaches for the management of this disorder.
 These criteria, as listed below, are given in the most current version of the IASP’s Complex regional pain syndrome: practical diagnostic and treatment guidelines (4th edition)
 where they are described as “state of the art” diagnostic criteria and “practical” guidelines. 

IASP-proposed revised CRPS clinical diagnostic criteria

A clinical diagnosis of CRPS can be made when the following criteria are met:

Continuing pain that is disproportionate to any inciting event

At least 1 symptom reported in at least 3 of the following categories:

Sensory: Hyperesthesia or allodynia

Vasomotor: Temperature asymmetry, skin color changes, skin color asymmetry

Sudomotor/edema: Edema, sweating changes, or sweating asymmetry

Motor/trophic: Decreased range of motion, motor dysfunction (eg, weakness, tremor, dystonia), or trophic changes (eg, hair, nail, skin)

At least 1 sign at time of evaluation in at least 2 of the following categories:

Sensory: Evidence of hyperalgesia (to pinprick), allodynia (to light touch, temperature sensation, deep somatic pressure, or joint movement)

Vasomotor: Evidence of temperature asymmetry (>1°C), skin color changes or asymmetry

Sudomotor/edema: Evidence of edema, sweating changes, or sweating asymmetry

Motor/trophic: Evidence of decreased range of motion, motor dysfunction (eg, weakness, tremor, dystonia), or trophic changes (eg, hair, nail, skin)

No other diagnosis better explaining the signs and symptoms

In addition, a slightly modified version of the above listing is used for CRPS research (as opposed to clinical) criteria. For these rules one must have the CRPS characteristics present in all four of the symptom categories and in at least two out of the four sign categories.

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