What Are the Best Diagnostic Tests for Complex Regional Pain Syndrome?

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Chapter 17 What Are the Best Diagnostic Tests for Complex Regional Pain Syndrome?

KEVIN C. CHUNG, MD, MS, AHMER K. GHORI, BA

HISTORY

The French physician Claude Bernard (1813–1878) first described the condition now called complex regional pain syndrome (CRPS).¹ His student, Silas Weir Mitchell, attributed it to autonomic instability and proposed the term causalgia for this diagnosis.² Since then, a variety of other names has also been used to describe this condition, including algodystrophy, sympathalgia, post-traumatic spreading neuralgia, and reflex sympathetic dystrophy. Although reflex sympathetic dystrophy was the widely accepted diagnostic term for a long time, the role of the sympathetic nervous system in the pathophysiology of this syndrome has not been confirmed. Therefore, in a consensus workshop of the International Association for the Study of Pain (IASP) in 1995, it was recommended that the condition known as reflex sympathetic dystrophy be called complex regional pain syndrome (CRPS).

Complex Regional Pain Syndrome: Causative Factors and Natural Progression

CRPS is divided into two subtypes, I and II, on the basis of an association with peripheral nerve pathology.³ CRPS I includes cases in whom no associated nerve pathology exists and in whom CRPS develops after a noxious event.³ For example, the reported incidence of CRPS I after various fractures is 1% to 2% (7–35% after Colles’ fractures).⁴ CRPS II includes cases in which there are known nerve pathology, and it mostly affects large nerves such as the median or sciatic nerves.³ For example, the reported incidence of CRPS II after peripheral nerve injuries is 2% to 5%; 10% to 26% of CRPS cases are idiopathic.⁴

CRPS may progress through three stages.¹ Stage 1 (acute) is a warm phase, and it is characterized by pain, sensory abnormalities, vasomotor dysfunction, edema, and sudomotor disturbances. Stage II (dystrophic) may be warm or cold, and it is characterized by worsening of stage I symptoms. In addition, motor and trophic (hair and nail growth) changes are first noted in stage II. Stage III (atrophic) is a cold phase in which pain and sensory disturbances decrease, but motor and trophic abnormalities worsen. In addition, atrophy of affected muscles may be noted. In some cases, the specific stages of CRPS may be difficult to identify clinically because they may blend into one another in a more continuous spectrum of manifestations. In one study, 13% of patients with acute CRPS had cold affected areas.² In some patients, the warm phase has been noted to persist for as long as 8 to 12 years after the initial diagnosis of CRPS.⁴ Overall, this staging system is widely accepted in literature.¹

COMPLEX REGIONAL PAIN SYNDROME: CLINICAL DIAGNOSIS

The IASP has suggested diagnostic criteria on multiple occasions,⁵ and these have been helpful in organizing the thought process in diagnosing CRPS. However, multiple studies have found that the IASP criteria have satisfactory sensitivity, but have poor specificity leading to a risk for overdiagnosis.⁶^–⁸ Because clinical symptoms can lead to overdiagnosis, in suspicious cases, more advanced tests that have better specificity may be administered to reduce false positives of clinical diagnosis. The clinical diagnosis criteria were revised in 2003, and the new standard that has better specificity¹ is described in Table 17-1. Clinical diagnosis has grade B level evidence (Table 17-2).

TABLE 17-1 Criteria for Clinical Diagnosis of Complex Regional Pain Syndrome

1. Continuing pain, which is disproportionate to any inciting event.

2. Patient must report at least three of the following symptoms:

a. Sensory: reports of hyperesthesia

b. Vasomotor: reports of temperature asymmetry and/or skin color changes and/or skin color asymmetry

c. Sudomotor/Edema: reports of edema and/or sweating changes and/or sweating asymmetry

d. Motor/Trophic: reports of decreased range of motion and/or motor dysfunction (weakness, tremor, dystonia) and/or trophic changes (hair, nail, skin)

3. Physician must verify at least two of the following signs:

a. Sensory: evidence of hyperalgesia (to pinprick) and/or allodynia (to light touch)

b. Vasomotor: evidence of temperature asymmetry and/or skin color changes and/or asymmetry

c. Sudomotor/Edema: evidence of edema and/or sweating changes and/or sweating asymmetry

d. Motor/Trophic: evidence of decreased range of motion and/or motor dysfunction (weakness, tremor, dystonia, neglect) and/or trophic changes (hair, nail, skin)

Adapted from Harden RN, Bruehl SP: Diagnosis of complex regional pain syndrome: Signs, symptoms, and new empirically derived diagnostic criteria. Clin J Pain 22:415–419, 2006.

TABLE 17-2 Grades of Recommendation for Diagnostic Tests

TEST	GRADE OF RECOMMENDATION^*
Clinical diagnostic criteria	B
Radiograph	B
Magnetic resonance imaging	B
Bone scanning	B
Sympathetic skin response	B

* A = good evidence (Level I studies with consistent finding) for or against recommending intervention; B = fair evidence (Level II or III studies with consistent findings) for or against recommending intervention; C = poor-quality evidence (Level IV or V with consistent findings) for or against recommending intervention; I = there is insufficient or conflicting evidence not allowing a recommendation for or against intervention.

CLINICAL DIAGNOSIS: SPECIFIC SYMPTOMS AND DIAGNOSTIC METHODS

The clinical symptoms of CRPS fall into four broad categories: (1) sensory, (2) vasomotor, (3) sudomotor, (4) motor/trophic. The most common findings in each category and common techniques to diagnose these symptoms are presented in the following sections.

Sensory Changes

Pain is the most frequently encountered symptom in CRPS; 81% of CRPS patients suffer severe pain.¹ The nature of pain is often described as burning or stinging, which typically starts at the distal end of an extremity and propagates proximally.⁹

Hyperesthesia and allodynia are reported in 65% of CRPS patients,¹ and they do not follow sensory nerve distribution patterns.⁹ This can be used to distinguish CRPS from nerve pathologies, which are limited to the affected nerve’s distribution. Mechanical allodynia can be tested by light touch or brushing over the affected area. Temperature allodynia may be assessed with warm and cold test tubes of water.

In addition, quantitative sensory testing, which is a computerized measure of temperature and vibrations sense,¹⁰ can be used for objective assessment of allodynia.¹¹^–¹³ Quantitative thermal testing may be done using a Marstock thermostimulator (Thermotest equipment; Somedic AB, Stockholm, Sweden).¹² This equipment has an electrode that is placed on the patient’s skin. Patients have control over cooling or heating the electrode, and they are asked to raise/lower temperature until it induces pain. The thermal thresholds of the affected and unaffected region are measured and compared with each other to look for allodynia. Similarly, quantitative vibration testing can be done using a handheld vibrator (TVR model, HV-13 D; Heiwa Electronic Industrial, Osaka, Japan).¹²