Physical Medicine and Rehabilitation for Complex Regional Pain Syndromes Workup

Updated: Feb 06, 2019
  • Author: Manish K Singh, MD; Chief Editor: Stephen Kishner, MD, MHA  more...
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Workup

Laboratory Studies

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  • No diagnostic criteria have been accepted uniformly for RSD, and no single special investigation has been proven sensitive and specific enough for diagnosing RSD. No criterion standard exists for making this clinical diagnosis, although some tests and findings may contribute to the diagnosis or help to diagnose or exclude other possible medical conditions.

  • As required, routine and specific blood tests, as well as other studies, should be performed to identify precipitating causes. The exact tests vary according to the body region involved, as well as according to the findings related to the history and physical examination.

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Imaging Studies

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  • Radiographic films may show patchy peri-articular demineralization within 3-6 weeks. The extent of osteoporosis is more than expected from disuse alone, and it is a common abnormality revealed on radiographs.

  • Three-phase bone scan:

    • A 3-phase bone scan may be helpful in revealing findings typical for the diagnosis of RSD and in excluding other conditions that could cause the patient's symptoms. A false-negative bone scan is fairly common.

    • The 3-phase bone scan often is considered sensitive and specific, particularly in the early phase (< 20 weeks) of the syndrome, but a study by Werner and colleagues reported that the 3-phase bone scan showed a diagnostic sensitivity of only 44%. [10]

    • According to Kozin and co-authors, scintigraphic abnormalities were reported in up to 60% of RSD patients and may be useful in arriving at the diagnosis of RSD, as well as in predicting which patients are likely to respond to systemic steroid therapy. [11]

    • Abnormally increased activity must be diffuse, not focal.

    • The most suggestive and sensitive findings on bone scan include diffuse increased activity, with juxta-articular accentuation uptake on the delayed images (phase 3).

    • Phases 1 and 2 are less sensitive and specific for RSD.

  • Imaging studies have shown to not be reliable screening tests in the differentiation between normal posttraumatic changes and those changes seen in CRPS due to a low positive predictive value (17-60%) and a moderate negative predictive value (79-86%). [12]

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Other Tests

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  • Skin temperatures - This measurement is simple, but important, to record during examination of the patient with RSD. Skin temperature is measured by (1) tactile perception, (2) surface thermistors, and (3) hand-held infrared thermometers:

    • Vascular changes in RSD

      • Hyperemic phase - Increase in the temperature of the skin early in the course of RSD

      • Cold limb - Decrease in the temperature of the skin later in the course of RSD

    • Thermography - This test demonstrates limb temperature differences quantitatively, but it is nonspecific. Bruehl and colleagues noted that thermography may be useful in situations in which sensitivity and specificity are equally important; an asymmetry cutoff of 0.6 º C appears optimal. [13] If specificity is more important, a cutoff of 0.8 º C or 1.0 º C may be considered.

  • Sudomotor function testing - Through the autonomic testing of 396 patients with pain, Chelminsky and colleagues demonstrated that abnormalities in resting sweat output, in resting skin temperature, and in a quantitative sudomotor axon reflex test predicted the diagnosis of CRPS I with 98% specificity [14] :

    • Sweat test - The sympathetic skin response (SSR) provides useful information on sudomotor dysfunction in patients with RSD; however, it is not possible yet to determine the final value of SSR for the diagnosis of RSD.

    • Quantitative sudomotor axon reflex test (QSART)

    • Chemical sweat test - This uses agents such as ninhydrin, cobalt blue, or starch iodine.

    • Testing sweat output - In QSART, the stimulated sweat output is greater and is prolonged when sympathetic hyperfunction is present.

  • Electrodiagnostic studies:

    • Results of electromyography (EMG) and nerve conduction studies (NCS) typically are within the reference range in RSD. In fact, if the EMG and nerve studies identify a nerve lesion, the condition is not by definition CRPS I but may instead be CRPS II.

    • Single-fiber EMG examination also shows no definite abnormalities.

    • The electrodiagnostic studies may be normal because C-fiber abnormalities cannot be well detected.

    • Patients with allodynia (demonstrating, for example, extreme pain even when clothing touches the involved limb or when a breeze blows across it) may have a difficult time tolerating EMG and NCS.

  • Quantitative sensory testing:

    • The purpose of quantitative sensory testing (QST) is to quantify perception thresholds objectively.

    • QST uses very precise, reproducible stimuli, allowing comparison of symptomatic areas with asymptomatic areas, comparison with age-matched and sex-matched controls, and changes with time or treatment. This provides the physician with information about the severity and progression of the sensory dysfunction.

    • The standard QST involves determination of vibrotactile detection thresholds (an Ab-fiber – mediated sensation), cool detection thresholds (an Ad-fiber – mediated sensation), and warm thermal thresholds (a C-fiber – mediated sensation) in appropriate areas. Heat and cold pain thresholds also are obtained with the patient's permission and with the patient controlling the amount of stimulus applied.

  • Laser Doppler imaging (see images below and Images 5-7):

    • Laser Doppler imaging, with appropriate stressors, provides a simple, fast, noninvasive, and painless method for the study of segmental autonomic function. This type of imaging study provides excellent spatial information, eliminates many sources of artifact, and can be used to rapidly and repeatedly test skin autonomic reflexes bilaterally.

    • Along with baseline images, mild stressors (inspiratory gasp, cold pressor positional dependency) are used to quantify skin vasoconstrictor reflexes (see Image 5). The first author has found these methods to be especially useful in helping to distinguish between sympathetically mediated and sympathetically independent pain conditions

      Normal laser Doppler study of the upper extremitie Normal laser Doppler study of the upper extremities. When the patient performs inspiratory gasp repeatedly during laser Doppler image acquisition, the transient capillary flow decreases are displayed easily and dramatically (as dark bands) in the pseudocolor image.
      Laser Doppler study of the upper extremities in a Laser Doppler study of the upper extremities in a patient with right hand reflex sympathetic dystrophy.
      Laser Doppler study of the lower extremities in a Laser Doppler study of the lower extremities in a 25-year-old woman with reflex sympathetic dystrophy in the right foot.
  • Diagnostic sympathetic ganglion block:

    • The IASP consensus group did not recognize response to sympathetic ganglion block as part of the diagnostic criteria for CRPS, since such responses, while often dramatic and impressive, are not universal.

    • Further, response to such blocks is more indicative of sympathetically maintained pain, which includes other etiologies in addition to CRPS.

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