Assessment of endothelial function in complex regional pain syndrome type I using iontophoresis and laser Doppler imaging

N. G. Shenker, P. I. Mapp, N. D. Harris and D. R. Blake

Royal National Hospital for Rheumatic Diseases, Upper Borough Walls, Bath BA1 1RL and University of Bath, Claverton Down, Bath BA2 7AY, UK

Correspondence to: E-mail: mpxns{at}bath.ac.uk

Sir, We read with interest the paper by Gorodkin and colleagues [1] describing their use of laser Doppler imaging (LDI) to measure the percentage increase in skin blood flow following the iontophoresis of acetylcholine and nitroprusside in patients with complex regional pain syndrome (CRPS). They found no differences in the blood flow responses of the limb affected by CRPS when compared with both the unaffected contralateral limb and the external control group.

Subtle bilateral changes occur more commonly than perhaps realized in patients with CRPS even though they present clinically with overwhelmingly unilateral signs. For example, warm and cold pain thresholds were different in the unaffected contralateral limbs of patients with CRPS when compared with normal control subjects, suggesting widespread changes [2]. Finger misidentification occurs on the contralateral normal hand, albeit at a much lower frequency than on the affected hand [3].

In a recent review of contralateral responses to local stimuli, we noted that responses in the contralateral limb may be affected by the experimental stimulus, thereby reducing comparative differences. Thus the contralateral limb may not be an appropriate control [4].

In order to correct for these confounding factors, Gorodkin and colleagues recruited an appropriate control group. Unfortunately, the results from this group were non-comparable to the experimental group due to calibration difficulties with the LDI. We too have had difficulties calibrating the LDI and now calibrate the machine before every use. We also use the ‘absolute perfusion’ setting to record and analyse repeated data over time.

Despite these difficulties, LDI is still a most useful research tool. This is because laser Doppler devices are more sensitive to small changes in blood flow than other methods, such as visual mapping, quantitative thermography and colorimetry. The LDI technique is also more reproducible (i.e. precise) than laser Doppler fibre-optic probe or single-point measurements because its larger spatial capacity can correct for skin's inherent heterogeneity. For example, we examined a group of 13 subjects repeatedly exposed to topical capsaicin using an analysis based on the percentage increase from baseline. We found that LDI gave 95% confidence of being within ±49% of the first reading compared with being within ±88% of the first reading using a fixed-point analysis.

No conflict of interested has been declared by the authors.

References

  1. Gorodkin R, Moore T, Herrick A. Assessment of endothelial function in complex regional pain syndrome type I using iontophoresis and laser Doppler imaging. Rheumatology 2004;43:727–30.[Abstract/Free Full Text]
  2. Kemler MA, Schouten JA, Gracely RH. Diagnosing sensory abnormalities with either normal values or values from contralateral skin: comparison of two approaches in complex regional pain syndrome I. Anesthesiology 2000;93:718.[CrossRef][ISI][Medline]
  3. Forderreuther S, Sailer U, Straube A. Impaired self-perception of the hand in complex regional pain syndrome (CRPS). Pain 2004;110:756–61.[CrossRef][ISI][Medline]
  4. Shenker N, Haigh R, Roberts E, Mapp P, Harris N, Blake D. A review of contralateral responses to a unilateral inflammatory lesion. Rheumatology 2003;42:1279–86.[Free Full Text]
Accepted 12 November 2004





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