Objective
Acupuncture has demonstrated efficacy as a treatment for fibromyalgia; however, predictors of short- and long-term analgesic response in this population are not well understood.
Methods
This manuscript describes a secondary analysis of a single-center, blinded, sham-controlled, randomized longitudinal acupuncture clinical trial in fibromyalgia. Baseline characterization included pressure pain threshold and pain interference, while residualized change in pain intensity from baseline to follow-up served as the primary outcome measure. Participants were randomized into groups that received verum (n = 36) or sham (n = 29) acupuncture treatment over a 12-week period (18 treatments) and were followed for 37 weeks from the initiation of treatment.
Results
Lower pressure pain thresholds at baseline were associated with greater analgesia only in the sham treatment group immediately following treatment, while those with higher pressure pain thresholds had greater analgesia with verum treatment (B = –13.43, P = 0.001). Additionally, greater perceived impact of pain at baseline was predictive of greater short-term analgesia irrespective of treatment. Pressure pain threshold was not found to be predictive of long-term differential treatment response (B= –1.71, P = 0.66). There was a significant difference in the relationship between perceived impact of pain at baseline and subsequent long-term analgesia between groups where those with greater perceived impact of pain displayed improved long-term analgesia for verum acupuncture compared to the sham group (B = –11.37, P = 0.004).
Conclusions
Our results support the use of a self-reported pain outcome in predicting long-term analgesia following acupuncture in fibromyalgia.

Key words: Acupuncture, Fibromyalgia, Chronic pain