Prism adaptation treatment for upper-limb complex regional pain syndrome: a double-blind randomized controlled trial

Abstract

Initial evidence suggested that people with complex regional pain syndrome (CRPS) have reduced attention to the affected side of their body and the surrounding space, which might be related to pain and other clinical symptoms. Three previous unblinded, uncontrolled studies showed pain relief after treatment with prism adaptation, an intervention that has been used to counter lateralised attention bias in brain-lesioned patients. To provide a robust test of its effectiveness for CRPS, we conducted a double-blind randomized controlled trial of prism adaptation for unilateral upper-limb CRPS-I. Forty-nine eligible adults with CRPS were randomized to undergo 2 weeks of twice-daily home-based prism adaptation treatment (n = 23) or sham treatment (n = 26). Outcomes were assessed in person 4 weeks before and immediately before treatment, and immediately after and 4 weeks after treatment. Long-term postal follow-ups were conducted 3 and 6 months after treatment. We examined the effects of prism adaptation vs sham treatment on current pain intensity and the CRPS symptom severity score (primary outcomes), as well as sensory, motor, and autonomic functions, self-reported psychological functioning, and experimentally tested neuropsychological functions (secondary outcomes). We found no evidence that primary or secondary outcomes differed between the prism adaptation and sham treatment groups when tested at either time point after treatment. Overall, CRPS severity significantly decreased over time for both groups, but we found no benefits of prism adaptation beyond sham treatment. Our findings do not support the efficacy of prism adaptation treatment for relieving upper-limb CRPS-I. This trial was prospectively registered (ISRCTN46828292).

Figure 1.

Schedule of data collection and interventions. LTFU, long-term follow-up; RS, research session.

Figure 2.

CONSORT diagram. Flow of participants through the study. CRPS, complex regional pain syndrome; RS1, research session 1; RS2, research session 2; RS3, research session 3; RS4, research session 4; LTFU1, long-term follow-up 1; LTFU2, long-term follow-up 2; intention-to-treat analysis, participants who received allocated intervention; per-protocol analysis, participants who completed allocated intervention, RS3-4 (CRPS severity), and LTFU1-2 (pain intensity). Note that 3 participants who were allocated to prism adaptation treatment did not attend RS2 or did not meet the eligibility criteria in RS2, and thus, they were not trained and did not receive any treatment and were not included in the intention-to-treat analysis.

Figure 3.

Prism adaptation procedure: In this example, a participant with left-CRPS is using rightward-shifting prisms (A–C), which induce adaptation towards the left (affected) side. For clarity of illustration, only one target (red circle) is represented in the figure. However, the treatment procedure involved 2 targets presented in the left and right side of space, and participants' pointing movements alternated between the left and right targets. (A) Prism goggles shift visual image to the right. The blue triangle represents a shift of visual perspective and perceived target location (pale red circle), relative to the real location of the target (light gray triangle, dark red circle). (B) Pointing movements initially err to the right. (C) Adaptive realignment results in correct pointing movements. (D) Goggles are removed and pointing movements err to the left (after-effect). CRPS, complex regional pain syndrome.

Figure 4.

Primary outcomes (intention-to-treat analysis). Mean (BCa 95% CI) current pain intensity (A) and CRPS severity scores (B) in prism adaptation (PA; orange circles) and sham treatment (blue diamonds) groups in each time point. LTFU1 and LTFU2, long-term follow-ups 1 and 2; RS1, RS2, RS3, and RS4, research sessions 1, 2, 3, and 4. Gray arrows indicate the treatment period. **Significant decrease in CRPS severity between RS2 and RS3, maintained at RS4, regardless of treatment, Ps_adj < 0.01. BCa 95% CI, bootstrapped bias-corrected and accelerated 95% confidence interval, CRPS, complex regional pain syndrome; PA, prism adaptation.