Abstract
BACKGROUND: Outcome expectancy is an important component of non-specific effect that may play an important role in pain research and clinical care. We sought to evaluate whether pretreatment expectancy predicts pain reduction in cancer survivors receiving electroacupuncture (EA) or battlefield acupuncture (BFA). METHODS: We analyzed data from a randomized clinical trial that compared EA and BFA versus wait list control (WLC) for chronic musculoskeletal pain in cancer survivors. Expectancy was measured by the Acupuncture Expectancy Scale (AES) at baseline. Pain severity was assessed using the Brief Pain Inventory (BPI) at baseline and week 12. For each treatment arm, multivariable regression models were used to evaluate the association between pretreatment expectancy and week 12 pain severity, controlling for baseline pain severity, age, sex, race, and education. RESULTS: Among 360 participants enrolled, the mean age was 62.1 years (SD 12.7), with 251 (69.7 %) women and 88 (24.4 %) non-white survivors. Pretreatment expectancy was similar for all groups at baseline (EA: 13.9 ± 3.6; BFA: 13.2 ± 3.7, WLC:12.8 ± 3.3, p = 0.14). Greater pretreatment expectancy was not significantly associated with greater pain reduction in any group, after adjusting for co-variates (EA: Coef. = -0.05, 95 % CI = -0.14 - 0.04, p = 0.28; BFA: Coef. = -0.07, 95 % CI = -0.16 - 0.02, p = 0.15; WLC: Coef. = -0.09, 95 % CI = -0.25 - 0.06, p = 0.23). CONCLUSIONS: Pretreatment expectancy did not predict pain reduction for either EA or BFA in cancer survivors. Our study contributes to the interpretation of analgesic effects of EA or BFA, beyond the notion of a mere 'placebo effect'.