BACKGROUND: Many randomized controlled trials (RCTs) of acupuncture reveal no significant differences between acupuncture and so-called placebo acupuncture. There is a strong tendency to replace the term "placebo" by the term "sham", because any needling stimulates a certain physiological response. However, neither concept accounts for the great diversity of results in RCTs comparing verum acupuncture and sham (placebo) acupuncture. Some trials have shown little or no difference, while other studies have found statistically significant differences. OBJECTIVE: Verum acupuncture and sham (placebo) acupuncture may achieve similar results to the extent that they share active constituents. We identified these common active constituents as dermatomes: the segmental structure of the human body. In our study, we tested the hypothesis that the more verum and sham (placebo) acupuncture share the same dermatomes, the closer the clinical outcomes will be, and vice versa. METHODS: All major databases were searched for RCTs that tested acupuncture versus sham (placebo) acupuncture. The dermatome charts of Hansen and Schliack were used to verify verum and sham (placebo) needling locations. Reported clinical outcomes were assessed in relation to the percentage of overlap between the dermatomes stimulated by acupuncture and sham (placebo) acupuncture. RESULTS: Our literature search yielded a total of 1738 references. Thirty-four studies met the inclusion criteria. The effects of sham (placebo) acupuncture varied according to the dermatomes stimulated: high overlap with those stimulated by verum acupuncture resulted in almost identical efficacy, while low overlap resulted in significant differences in efficacy. Clinical outcomes were similar when verum acupuncture and sham (placebo) acupuncture shared the same dermatomes (p < 0.01). DISCUSSION: The findings of this review confirm our hypothesis. Acupuncture studies that employed verum and sham locations on overlapping dermatomes helped to create a mediocre to negative picture of acupuncture's efficacy. The segmental structure of the body with its interconnected reflex system offers an additional neurophysiological explanation for the effectiveness of acupuncture applied to structures segmentally innervated by the spinal and visceral nervous system. Further comparative acupuncture studies should be based on knowledge of segmental anatomy. In testing verum acupuncture versus sham acupuncture, the chosen sham acupuncture needling locations should be situated on non-overlapping dermatomes.

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