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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)., 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., Methods: Thirty patients with CRPS, 33 with rheumatology conditions and 45 healthy controls viewed two images: a bistable spatial image and a control image. For each image participants recorded the frequency of percept change in 1 min and reported any changes in somatosensation., 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., 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., (Copyright © 2010 European Federation of International Association for the Study of Pain Chapters. Published by Elsevier Ltd. All rights reserved.)

Nociceptive pain in response to peripheral noxious stimuli, and inflammatory pain resulting from tissue damage, serve as warnings that normal bodily function cannot resume until the stimulus abates or the tissue repairs. Stimuli cause numerous receptors, ion channels and other cellular machinery to respond, and propagate signals to the central nervous system, where this information is processed and perceived as pain. In healthy individuals, tissue damage results in physiologic--generally reparative--changes that lead to heightened sensory perception and, often, pain. In rheumatic diseases, the joint pain bears much in common with chronic inflammatory pain, but the underlying disease state is typically much more intricate and no reparative function is evident. Addressing the complex pains of rheumatic disease remains an ongoing challenge. Pain signaling pathways involve many molecular components that could potentially be targets for pharmacotherapeutic intervention, but the complexity of this system might also mean that multiple sites must be affected simultaneously to disrupt propagation of pain signals. In addition, to be therapeutically viable, pain drugs must be safe and not alter tactile sensory function, alertness or cognitive function. In this article we review the molecular functions in nociceptive, inflammatory and rheumatic pain pathways, and the therapeutic options they might offer.

In spite of pain in the CRPS limb, clinical observations show patients pay little attention to, and fail to care for, their affected limb as if it were not part of their body. Literature describes this phenomenon in terms of neurological neglect-like symptoms. This qualitative study sought to explore the nature of the phenomenon with a view to providing insights into central mechanisms and the relationship with pain. Twenty-seven participants who met the IASP CRPS classification were interviewed using qualitative methods to explore feelings and perceptions about their affected body parts. These semi-structured interviews were analysed utilising principles of grounded theory. Participants revealed bizarre perceptions about a part of their body and expressed a desperate desire to amputate this part despite the prospect of further pain and functional loss. A mismatch was experienced between the sensation of the limb and how it looked. Anatomical parts of the CRPS limb were erased in mental representations of the affected area. Pain generated a raised consciousness of the limb yet there was a lack of awareness as to its position. These feelings were about the CRPS limb only as the remaining unaffected body was felt to be normal. Findings suggest that there is a complex interaction between pain, disturbances in body perception and central remapping. Clinically, findings support the use of treatments that target cortical areas, which may reduce body perception disturbance and pain. We propose that body perception disturbance is a more appropriate term than 'neglect-like' symptoms to describe this phenomenon.

Abstract: Knowledge of the position of one’s limbs is an essential component of daily function and relies on complex interactions of sensorimotor body schema-related information. Those with Complex Regional Pain Syndrome (CRPS) express difficulty in knowing where their affected limb is positioned. The aim of this study was to determine the degree to which experimental data supported the reported difficulty in limb position sense. A controlled experimental design was used to measure upper limb position accuracy amongst those with CRPS of one arm. Position accuracy was individually measured in both arms and compared to a known target position. Video captured each of 36 trials (half with arm in full view and half with vision obscured). The error in degrees between actual and known targets was determined using video analysis software. The Brief Pain Inventory measured pain. A subjective mental image representation of both upper limbs was documented. The CRPS group had moderate pain intensity and were significantly less accurate in positioning both the affected and unaffected limbs compared to controls (p <0.001). Position accuracy of the CRPS affected limb significantly improved with vision (8.3° in view, 10.7° not in view). Subjective mental representations of the affected limb were visualised as distorted. Evidence of bilateral arm positioning impairments in unilateral arm CRPS suggests that central mechanisms are involved. Cortical reorganisation in regions associated with the body schema (i.e. primary somatosensory and parietal cortices) is proposed as an explanation. The exact relationship between pain and limb position deficits requires further exploration. [Copyright &y& Elsevier]