Fair-quality evidence demonstrates the effectiveness of mirror therapy in phantom limb pain in individuals with amputations, according to the authors of a systematic review and meta-analysis published in Clinical Rehabilitation.
Although the number of studies investigating mirror therapy in reducing phantom limb sensation and pain has increased, the overall effectiveness of the treatment is unclear. A 2016 meta-analysis by Barbin et al showed that currently available evidence is “inadequate” and studies are heterogeneous in terms of their methodologies and findings.
Therefore, the authors of this study conducted a systematic review and meta-analysis to evaluate the most updated evidence and the effects of mirror therapy on short- and long-term phantom limb pain. To address high heterogeneity in control therapies, they performed a subgroup analysis to determine whether the type of control therapy had a confounding role in effect size estimation.
Nine electronic databases were searched from inception through May 10, 2021 to identify potential studies for inclusion.
The study authors retrieved a total of 2397 articles and identified 11 comparative studies that met the inclusion criteria. These trials were published between 2003 and 2020 and included 491 participants, of whom 417 had unilateral lower-limb amputations, 54 had unilateral upper-limb amputations, and 20 had bilateral lower-limb amputations. Sample sizes for each study ranged from 15 to 92 patients.
Reasons for amputations included diabetes, tumor, trauma, and a range of other medical conditions.
Nine of the 11 studies used the visual analog scale (VAS) to measure pain intensity; 1 study used the Numeric Rating Scale (NRS).
Qualitative synthesis showed that 1 study reported only on phantom limb sensation, performing no outcome measurements of phantom limb pain. Another study did not report on appropriate phantom limb pain numerical outcomes. As a result, only 9 trials with a total of 372 patients were included in the quantitative synthesis, with study quality ranging from fair to good.
The VAS was used in 8 studies, and the NRS was used in only 1 study. Three studies used a multidimensional assessment of pain, as measured by the McGill Pain Questionnaire, but 1 of these studies did not report enough data. Frequency of phantom limb pain was evaluated in 3 studies with NRS or number of episodes per day. Phantom limb pain duration was evaluated in 1 study using minutes per day; another study evaluated psychological status using Short-Form 36 (SF-36) and depression using the Beck Depression Inventory.
Compared with control group findings, pooled standardized mean differences (SMD) showed that the between-group differences was statistically significant for alleviating pain intensity (-0.81; 95% CI, -1.36 to -0.25; P =.005). However, the funnel plot was asymmetrical, indicating publication bias in terms of pain; the study authors concluded this may have been due to the limited number of included studies and between-study heterogeneity. Two studies were excluded, and the significance of the pooled SMD for pain intensity remained (-0.40; 95% CI, -0.66 to -0.14; P =.003).
In 3 studies, pooled SMD showed that differences between mirror therapy vs covered-mirror therapy were not statistically significant in terms of pain intensity alleviation (-0.25; 95% CI, -0.73 to 0.24; P =.032). Mental visualization findings across 4 studies showed that differences were statistically significant in terms of alleviating pain intensity, favoring mirror therapy (-1.47; 95% CI, -2.42 to -0.52; P =.002).
Four studies reported on treatment effect at midterm follow-up — typically at month 3 — and found that pooled SMD demonstrated statistically significant between-group differences in alleviating pain intensity (-0.59; 95% CI, -1.16 to -0.03; P =.046), favoring mirror therapy.
An additional 4 studies reported on the treatment effect at long-term follow-up — typically a 6-month period — and demonstrated that differences were statistically significant between groups (-1.21; 95% CI, -2.22 to -0.20; P =.02), favoring mirror therapy.
Fair-quality evidence quality, according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system, showed that mirror therapy had a moderate effect on pain reduction after the intervention ended. This quality was downgraded by the high heterogeneity, small sample size, and/or wide CIs.
Of note, 3 studies did not report information about adverse effects, 5 reported no increase in phantom pain or adverse effects, and 1 reported that 2 patients experienced brief reactions of less than 2 minutes of grief upon viewing the reflected lower limb. Further, 1 study reported that a participant experienced a pain increase during mirror therapy; and 1 study reported that, in the mirror therapy group, 4 patients experienced short phantom limb pain events during treatment and 2 patients had minor signs of nausea, emotional reaction, and increased transpiration when treatment began.
Study limitations included the small number of randomized controlled trials that met the inclusion criteria, the relatively small sample sizes of each study, the high heterogeneity, and the inclusion of only 3 studies from which to draw conclusions about long-term follow-up.
“The present study provides the latest evidence to support the implementation of mirror therapy as an alternative treatment to reduce phantom limb pain in [individuals with amputations] compared with the control in the short term,” the researchers concluded. “It is recommended that further research, including larger sample sizes and longer follow-up period studies in consideration of various covariates … should be performed.”
Wang F, Zhang R, Zhang J, et al. Effects of mirror therapy on phantom limb sensation and phantom limb pain in amputees: A systematic review and meta-analysis of randomized controlled trials. Clin Rehabil. Published online July 24, 2021. doi:10.1177/02692155211027332