Limb-specific autonomic dysfunction in complex regional pain syndrome modulated by wearing prism glasses.

In unilateral upper-limb complex regional pain syndrome (CRPS), the temperature of the hands is modulated by where the arms are located relative to the body midline. We hypothesized that this effect depends on the perceived location of the hands, not on their actual location, nor on their anatomical alignment. In 2 separate cross-sectional randomized experiments, 10 (6 female) unilateral CRPS patients wore prism glasses that laterally shifted the visual field by 20°. Skin temperature was measured before and after 9-minute periods in which the position of one hand was changed. Placing the affected hand on the healthy side of the body midline increased its temperature (Δ°C=+0.47 ± 0.14°C), but not if prism glasses made the hand appear to be on the body midline (Δ°C=+0.07 ± 0.06°C). Similarly, when prism glasses made the affected hand appear to be on the healthy side of the body midline, even though it was not, the affected hand warmed up (Δ°C=+0.28 ± 0.14°C). When prism glasses made the healthy hand appear to be on the affected side of the body midline, even though it was not, the healthy hand cooled down (Δ°C=-0.30 ± 0.15°C). Friedman's analysis of variance and Wilcoxon pairs tests upheld the results (P<0.01 for all). We conclude that, in CRPS, cortical mechanisms responsible for encoding the perceived location of the limbs in space modulate the temperature of the hands.

Using visual illusion to reduce at-level neuropathic pain in paraplegia.

Neuropathic pain after spinal cord injury is not well understood and is difficult to treat. One possible cause is mismatch between motor commands and sensory feedback. This two-part study in five paraplegic patients investigated whether a visual illusion aimed to correct this mismatch reduces pain. In study 1, patients undertook three conditions: (i) virtual walking: with a mirror placed in front of a screen, patients aligned their own upper body with a film of a lower body walking. Patients imagined walking and 'watched themselves' walk; (ii) guided imagery; (iii) watching a film. One patient withdrew from virtual walking because of distress. For all patients, the mean (95% CI) decrease in pain (100 mm VAS) was 42 mm (approximately 65%) (11-73 mm) for virtual walking, 18 mm (4-31 mm) for guided imagery and 4mm (-3 to 11 mm) for watching the film. Mean (95% CI) time to return to pre-task pain was 34.9 min (20.1-49.8 min) for virtual walking; 13.9 min (-0.9 to 28.8 min) for the guided imagery and 16.3 min (1.5-31.2 min) for the film. To investigate its clinical utility, four patients underwent virtual walking every weekday for 3 weeks. Mean (95% CI) decrease in pain was 53 mm (45-61 mm) at post training and 43 mm (27-58 mm) at 3-month follow-up. Virtual walking may be a viable treatment for pain after spinal cord injury. A clinical trial seems warranted.