Making a Complex Regional Pain Syndrome Diagnosis: Avoid Overdiagnosis

• Complex Regional P​ain Syndrome MAKING A DIAGNOSIS
  Considerable confusion has been generated by a failure
  to understand the recent work from the IASP. In 1994, when the IASP
  produced the new diagnostic entity of CRPS, it was descriptive, and
  general and based on a consensus.119
  Deliberately, it did not imply any etiology or pathology (including any
  direct role for the SNS). The intention was to provide an officially
  endorsed set of standardized diagnostic criteria to improve clinical
  communication and facilitate research.118
  In other words, this was intended as a starting point from which
  individual researchers could move forward. It was not thought of as a
  mature clinical diagnostic device.
  Since their original publication, the diagnostic
  criteria have been validated, refined, and developed. The validation
  studies suggest that the original criteria are adequately sensitive within the context of a pain clinic
  (i.e., they rarely miss a case of actual CRPS); however, the criteria
  cause problems of overdiagnosis because of poor specificity.58,80
  Comparison of CRPS patients to other proved pain states, such as
  chronic diabetic patients with ascending symmetric pain, whose
  neuropathy is confirmed by nerve conduction studies, also show that the
  criteria are very sensitive but have low specificity, so that a
  diagnosis of CRPS may be erroneous in up to 60% of cases.22
  Other problems are evident. For example, the criteria
  assume that any sign or symptom of vasomotor, sudomotor, and
  edemarelated change is sufficient to justify the diagnosis and there is
  no possibility of providing greater diagnostic or prognostic accuracy
  by observing more than one of these features. An additional weakness is
  the failure to include motor or trophic signs and symptoms. Numerous
  studies have described various signs of motor dysfunction (e.g.,
  dystonia, tremor) as important characteristics of this disorder, and
  trophic changes have frequently been mentioned in historical clinical
  descriptions.26,28 These differentiate CRPS from other pain syndromes.58,138
  Finally, the wording of the criteria permits diagnosis based solely on
  patientreported historical symptoms. This may be inappropriate in the
  context of litigation.
  Factor analysis of 123 CRPS patients has indicated that the features cluster into four statistically distinct subgroups.80
• A set of signs and symptoms indicating abnormalities in pain processing (e.g., allodynia, hyperalgesia, hyperpathia)
• Skin color and temperature changes, indicating vasomotor dysfunction
• Edema and abnormalities of sweating
• Motor and trophic signs and symptoms
  The statistical separation of edema and sudomotor
  dysfunction from vasomotor instability and the finding of motor and
  trophic abnormalities are at variance with the original IASP criteria,
  which were therefore modified22,58,80 (Table 23-3).
  The important changes are inclusion of clinical signs, their separation
  from symptoms, and the inclusion of features of motor abnormalities and
  trophic changes. Intriguingly, these subgroups are virtually identical
  to those suggested by our group a decade earlier.3
  Statistical analysis has been undertaken to investigate
  sensitivity and specificity of decision rules for diagnosis of CRPS
  compared to neuropathic pain of a proved non-CRPS cause using these
  criteria22 (Table 23-4).
  These propose different diagnostic criteria depending on the clinical
  circumstances. Thus, for purely clinical diagnosis, the criteria
  provide a sensitivity of 0.85 and a specificity of 0.69, whereas for
  research diagnosis, the criteria provide a sensitivity of 0.70 and
  specificity of 0.94, because, in the former circumstance, one wishes to
  avoid failing to offer treatment to a possible candidate while in the
  latter situation one is more concerned to be investigating a
  homogeneous group in whom the diagnosis cannot be in doubt.
  It is critical to understand that the Bruehl modification of the original IASP criteria24 given in Table 23-3 apply to the diagnosis of CRPS within a pain clinic setting
  and are therefore intended to differentiate CRPS from other causes of
  chronic pain within that setting. They do not apply directly to the
  diagnosis of CRPS within the context of an orthopaedic practice. The
  reason for this apparent conundrum is that the precise nature of CRPS
  remains unclear and it is therefore a diagnosis of exclusion.
  Conditions from which CRPS must be distinguished in a pain clinic
  (e.g., neuropathic pain in association with diabetic neuropathy) are
  different from those which apply in an orthopaedic or fracture clinic
  (e.g., soft tissue infection or stress fracture). Therefore, the
  diagnostic criteria must be slightly different, just as slightly
  different criteria are required within a pain clinic for diagnosis of
  CRPS depending on whether the diagnosis is being made for clinical or
  research purposes.
  Atkins et al.2,3,4 proposed a set of diagnostic criteria for CRPS specifically in an orthopaedic context(Table 23-5).
  These were derived empirically from a less formal but similar process
  to the IASP consensus approach. The criteria were designed as far as
  possible to be objective, but the patient’s veracity was assumed, so no
  attempt was made to separate reports of vasomotor or sudomotor
  abnormalities from observation of them. A number of the criteria are
  quantifiable,2,3,51 which allows their powerful use to investigate treatment.53,54,105
  The original criteria were developed in the context of CRPS of the hand
  following Colles’ fracture of the wrist, but they have subsequently
  been generalized for use in the diagnosis of CRPS in other orthopaedic
  scenarios and in the lower limb.13,135
  Diagnosis by these criteria, when used after Colles’ fracture, maps
  virtually exactly with the Bruehl criteria, suggesting their
  reliability.147
  Clinical Diagnosis in an Orthopaedic Setting
  1. Pain
  A history of excessive pain is elicited. Abnormalities
  of pain perception are examined in comparison with the opposite normal
  side. Excessive tenderness is found by squeezing digits in the affected
  part between thumb and fingers. This may be quantitated using
  dolorimetry but this is usually a research tool.4,6
  Allodynia is demonstrated by fine touch and hyperalgesia using a pin.
  Hyperpathia is examined by serial fine touch or pin prick.
  TABLE
  23-3 Modified International Association for the Study of Pain
  Diagnostic Criteria for Complex Regional Pain Syndrome (CRPS)

| General definition of the syndrome
CRPS describes
an array of painful conditions that are characterized by a continuing
(spontaneous and/ or evoked) regional pain that is seemingly
disproportionate in time or degree to the usual course of any known
trauma or other lesion. The pain is regional (not in a specific nerve
territory or dermatome) and usually has a distal predominance of
abnormal sensory, motor, sudomotor, vasomotor, and/or trophic findings.
The syndrome shows variable progression over time.
To make the clinical diagnosis, the following criteria must be met (sensitivity of 0.85 specificity of 0.69)
1. | Continuing pain, which is disproportionate to any inciting event
2. | Must report at least one symptom in three of the four following categories:
| | Sensory
| | | Reports of hyperesthesia and/or allodynia
| | Vasomotor
| | | Reports of temperature asymmetry and/or skin color changes and/or skin color asymmetry
| | Sudomotor/edema
| | | Reports of edema and/or sweating changes and/or sweating asymmetry
| | Motor/trophic
| | | Reports of
decreased range of motion and/or motor dysfunction (weakness, tremor,
dystonia) and/ or trophic changes (hair, nail, skin)
3. | Must display at least one sign at time of evaluation in two or more of the following categories:
| | Sensory
| | | Evidence of
hyperalgesia (to pinprick) and/or allodynia (to light touch and/or
temperature sensation and/or deep somatic pressure and/or joint
movement)
| | Vasomotor
| | | Evidence of temperature asymmetry (>1°C) and/or skin color changes and/or asymmetry
| | Sudomotor/edema
| | | Evidence of oedema and/or sweating changes and/or sweating asymmetry
| | Motor/trophic
| | | Evidence of
decreased range of motion and/or motor dysfunction (weakness, tremor,
dystonia) and/or trophic changes (hair, nail, skin)
4. | There is no other diagnosis that better explains the signs and symptoms.
For research purposes, diagnostic decision rule should be at least one symptom in all four
symptom categories and at least one sign (observed at evaluation) in
two or more sign categories (sensitivity of 0.70, specificity of 0.94).
From Bruehl et al.22 and Harden et al.80
2a. Vasomotor instability
Vasomotor instability is often transitory and so it may
not be present at the time of examination. If the patient is reliable,
then a history confirms its presence. Visual inspection is the usual
means of diagnosis.
Thermography can be used to quantitate temperature
difference between the limbs. This is greater in CRPS than other pain
syndromes,128,162
and this can be used to distinguish CRPS from other causes of
neuropathic pain. However, thermography has not been validated within
an orthopaedic context and must therefore be used with caution. It is
not usually used in an orthopaedic context.
2b. Abnormal sweating
Whether this feature should be considered with vasomotor instability as proposed by Atkins et al.3,6 or should be with edema as suggested recently by Harden et al.80
is not yet clear. As for vasomotor instability, the feature is
inconstant and it may be necessary to rely on history. Excessive
sweating is usually clinically obvious. In a doubtful case, the
resistance to a biro or pencil gently stroked across the limb is
useful. The extent of sweating can be quantified by iontophoresis but
this is rarely undertaken.
3. Edema and swelling
This is usually obvious on inspection. In the hand, it
may be quantified by hand volume measurement. Similarly, skinfold
thickness and digital circumference may be measured.3,6
4. Loss of joint mobility and atrophy
Loss of joint mobility is usually diagnosed by standard
clinical examination. The range of finger joint movement may be
accurately quantified.3,6,51 As outlined here, atrophy will affect every tissue within the limb.
5. Bone changes
Radiographic appearances and bone scans are discussed
earlier. CRPS does not cause arthritis and joint space is preserved.
Sudeck’s technique of assessing bone density by radiographing two
extremities on one plate120,145 remains
useful but densitometry is not usually helpful.156 A normal bone scan without radiographic osteoporosis virtually excludes adult CRPS.
TABLE
23-4 Diagnostic Sensitivity and Specificity for the International
Association for the Study of Pain Modified Criteria (see Table 23-3)
in Distinguishing Patients with Complex Regional Pain Syndrome (CRPS)
from Patients with Neuropathic Pain from a Documented Non-CRPS Cause
| --- | Decision rule | Sensitivity | Specificity |
| --- | --- | --- |
| 2 + sign categories and 2 + symptom categories | 0.94 | 0.36 |
| 2 + sign categories and 3 + symptom categories | 0.85 | 0.69 |
| 2 + sign categories and 4 symptom categories | 0.70 | 0.94 |
3 + sign categories and 2 + symptom categories <td align="right" colspan="1" rowspan="1" style="border-style: solid; border-color: rgb(221, 221, 221); box-si