Pain and other symptoms of CRPS can be increased by ambiguous visual stimuli – an exploratory study

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Hall, J. ; Harrison, S. ; Cohen, H. ; McCabe, C. ; Harris, N. ; Blake, D. R. (2010)

Background: Visual disturbance, visuo-spatial difficulties, and exacerbations of pain associated with these, have been reported by some patients with Complex Regional Pain Syndrome (CRPS). \ud \ud Aims: We investigated the hypothesis that some visual stimuli (i.e. those which produce ambiguous perceptions) can induce pain and other somatic sensations in people with CRPS.\ud \ud Methods: Thirty patients with CRPS, 33 with rheumatology conditions and 45 healthy controls viewed 2 images: a bistable spatial image and a control image. For each image participants recorded the frequency of percept change in 1 minute and reported any changes in somatosensation.\ud \ud Results: 73% of patients with CRPS reported increases in pain and /or sensory disturbances including changes in perception of the affected limb, temperature and weight changes and feelings of disorientation after viewing the bistable image. Additionally, 13% of the CRPS group responded with striking worsening of their symptoms which necessitated task cessation. Subjects in the control groups did not report pain increases or somatic sensations.\ud \ud Conclusions: It is possible to worsen the pain suffered in CRPS, and to produce other somatic sensations, by means of a visual stimulus alone. This is a newly described finding. As a clinical and research tool, the experimental method provides a means to generate and exacerbate somaesthetic disturbances, including pain, without moving the affected limb and causing nociceptive interference. This may be particularly useful for brain imaging studies.
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