Through the Looking Glass -- Mirror Therapy Provides Pain Relief for CRPS Mirror Therapy for Chronic Complex Regional Pain Syndrome

Background: Complex regional pain syndrome (CRPS) is a debilitating condition often refractory to treatment. In the affected limb, the patient may experience burning, allodynia, hyperalgesia, weakness, tremor, muscle spasm, edema, and changes in temperature and vascular tone. Why this happens is unclear. One hypothesis suggests a mismatch between proprioceptive feedback and motor action causes CNS sensory distortion and pain. If true, the misperception of continued pain might correct itself if the offending proprioception could be suppressed. Visual feedback can substitute for impaired proprioception if patients watch their feet when they walk. Similarly, a sensory denervated, pseudoathetotic limb can be controlled with visual guidance. In 2007, Chan reported remarkable improvement in phantom limb pain when the patient experienced the illusion of limb movement through use of a mirror. Objective: To determine if mirror therapy can reduce pain and improve motor function in stroke patients with CRPS type 1 (no identifiable peripheral nerve injury). Participants: 11 men and 13 women (median age, 62 years) who developed CRPS in the paretic arm at 7 to 21 months after stroke. Methods: 8 patients were randomly assigned to mirror therapy and tried to move their painful arm while viewing the reflected image of the normal arm attempting the same movement. Controls either did the same but with the mirror covered (n=8) or imagined the same movements with their eyes closed (n=8). All performed the assigned task for 30 minutes daily. After 4 weeks, pain severity was measured using a visual analogue scale (VAS scores ranged from 0 to 100 mm). The 2 control groups then crossed over to mirror therapy for 4 weeks while the group originally assigned to mirror therapy continued as before. Outcome evaluators were blinded to group assignments. Results: All 3 groups had comparable baseline pain (VAS median score, 63 mm). After 4 weeks, pain intensity increased to 80 for both control groups but dropped to 8 in the mirror therapy group. Seven mirror therapy patients reported reduced pain versus 1 for sham mirror and 2 for mental imagery. Reduced pain was demonstrated in 93% of control patients who crossed over to mirror therapy. Motor function, brush-induced allodynia, and edema also improved with mirror therapy. Conclusions: Mirror therapy reduces pain and enhances motor function in the paretic arm of stroke patients with chronic CRPS type 1. Reviewer's Comments: There must be a fascinating principle at work here regarding the dubious ways in which the brain processes sensory information. One has to wonder how often the brain plays similar tricks on itself in both health and disease. (Reviewer-Michael Jacewicz, MD).