Measuring the placebo effect in carpal tunnel syndrome

Background: The placebo effect can account for part of the improvement seen in patients undergoing any type of treatment, be it surgical or pharmacological. The objective of this study is to quantify the placebo effect in carpal tunnel syndrome treatment.

Materials and methods: A double-blinded randomized trial was performed with 68 patients suffering from mild to moderate carpal tunnel syndrome, divided into two groups with no statistically significant differences regarding age, weight, or degree of nerve compression. The patients were evaluated clinically and electromyographically before and after 2 months of treatment with either palmitoylethanolamide (PEA) or placebo.

Results: The results, comparing the two groups, showed an improvement in both groups on a visual analogue scale (VAS) and Levine's questionnaire, which have been reported to show statistical differences in only a few items. In the placebo group, the mean age was 53.32 years (±13.43) and the BMI was 28.85 kg/m² (±4.84). Before treatment, the average symptom severity score (SSS) on the Levine questionnaire was 2.57 (±0.74) and the functional status score (FSS) was 2.24 (±0.66). After treatment, these decreased to 2.11 (±0.81) and 1.96 (±0.77), being statistically nonsignificant for SSS (p = 0.0865) but significant for FSS (p = 0.0028). VAS showed a statistically nonsignificant decrease from 4.06 to 3.25 (p = 0.3407). After placebo treatment, SSS, FSS, and VAS improved by 0.46, 0.28, and 0.81 points or 17.89%, 12.5%, and 19.95%, respectively.

Conclusions: These results show an improvement in the studied parameters by up to 20%, but when compared with those published in literature, these show great variability due to the wide variety of factors involved in the placebo effect. Several factors that affect the placebo effect are discussed, and the present work tries to quantify it in carpal tunnel syndrome.

Level of evidence: Level 2 of evidence according to "The Oxford 2011 Level of Evidence."