'Pseudo-neglect' in CRPS is closer to 'anti-neglect' than to classical hemi-neglect?

Attention can exert a powerful effect on the perception of pain sensations, so much so that distraction can have an analgesic effect on acute pain equal to that of opiates [21]. Spatial attention can modulate heat pain detection and discrimination, as demonstrated by studies in which a pain stimulus is presented following a cue, which is located either on the same side as the stimulus or on the opposite side. The cue on the opposite side leads to increased error rates and response latencies for heat pain stimuli [2,8]. In turn, a lateralized visual discrimination task is performed more rapidly when it is preceded by a painful stimulus on the same side as the visual stimulus than on the opposite side. Similarly, eye orientation to the side of the painful stimulus leads to higher pain ratings [18]. These results suggest that visual stimuli and painful stimuli can interact by shifting spatial attention to one or the other side of the body. In this issue of PAIN, Reinersmann et al. report that the shift of the visual subjective body midline (vSM) towards the left side was greater in patients with complex regional pain syndrome (CRPS) than in patients with other types of chronic pain, or in healthy controls [20]. This leftward bias is referred to as ‘pseudo-neglect’ and is interpreted to be the result of right hemispheric dominance in spatial perception, including perceptual representation of one’s own body (body schema). This observation may be related to the finding that vSM deviates to the affected side in patients with CRPS and that this effect can be reversed by nerve blockades with local anesthetic or ischemia [23]. Other body schema abnormalities in patients with CRPS include the finding that such patients take longer to recognize the laterality of a hand in a picture when the pictured hand corresponds to the laterality of the affected hand [17]. This study adds interesting detail to the concept of CRPS, which has evolved from a ‘‘sympathetically-maintained pain’’ to a syndrome of sensory-motor-autonomic dysfunctions [1]. Reinersmann et al. demonstrated that the shift in visual subjective midline was specific to CRPS vs. other upper limb pain syndromes. However, the relationship of the term ‘pseudo-neglect’ as used in this paper to the classical hemi-neglect is uncertain. Hemi-neglect is failure of a subject ‘to report, respond, or orient to meaningful stimuli contralateral to the brain lesion’ [10]. Visual spatial hemi-neglect is most commonly observed after lesions of the right parietal cortex, but can also occur after right sided lesions of the prefrontal cortex, the superior temporal gyrus, the frontal operculum, or the thalamus [12,25]. The phenomenon of extinction is considered to be a subtle form of neglect [10,11], which is measured by a dual simultaneous stimulation (DSS) protocol. Extinction is the failure to report stimuli on the affected (left) side of the body when an identical simultaneous stimulus occurs on the