Pain
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Randomized Controlled Trial
Brain networks predicting placebo analgesia in a clinical trial for chronic back pain.
A fundamental question for placebo research is whether such responses are a predisposition, quantifiable by brain characteristics. We examine this issue in chronic back pain (CBP) patients who participated in a double-blind brain imaging (functional magnetic resonance imaging) clinical trial. We recently reported that when the 30 CBP participants were treated, for 2 weeks, with topical analgesic or no drug patches, pain and brain activity decreased independently of treatment type and thus were attributed to placebo responses. ⋯ Additionally, by means of frequency domain contrasts, we observe that at baseline, left dorsolateral prefrontal cortex high-frequency oscillations also predicted treatment outcomes and identified an additional set of functional connections distinguishing treatment outcomes. Combining medial and lateral prefrontal functional connections, we observe a statistically higher accuracy (0.9) for predicting posttreatment groups. These findings indicate that placebo response can be identified a priori at least in CBP, and that neuronal population interactions between prefrontal cognitive and pain processing regions predetermine the probability of placebo response in the clinical setting.
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Randomized Controlled Trial
The hidden effects of blinded, placebo-controlled randomized trials: an experimental investigation.
The knowledge of having only a 50% chance of receiving an active drug can result in reduced efficacy in blinded randomized clinical trials (RCTs) compared to clinical practice (reduced external validity). Moreover, minor onset sensations associated with the drug (but not with an inert placebo) can further challenge the attribution of group differences to drug-specific efficacy (internal validity). We used a randomized experimental study with inert placebos (inert substance) vs active placebos (inducing minor sensations), and different instructions about group allocation (probability of receiving drug: 0%, 50%, 100%). ⋯ Moreover, minor drug onset sensations can challenge internal validity. Effect sizes for these mechanisms are medium, and can substantially compete with specific drug effects. For clinical trials, new study designs are needed that better control for these effects.
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Randomized Controlled Trial
Associations between daily chronic pain intensity, daily anger expression, and trait anger expressiveness: an ecological momentary assessment study.
Links between elevated trait anger expressiveness (anger-out) and greater chronic pain intensity are well documented, but pain-related effects of expressive behaviors actually used to regulate anger when it is experienced have been little explored. This study used ecological momentary assessment methods to explore prospective associations between daily behavioral anger expression and daily chronic pain intensity. Forty-eight chronic low back pain (LBP) patients and 36 healthy controls completed electronic diary ratings of momentary pain and behavioral anger expression in response to random prompts 4 times daily for 7 days. ⋯ Overlap with trait and state negative affect did not account for study findings. This study for the first time documents lagged within-day influences of behavioral anger expression on subsequent chronic pain intensity. Trait anger regulation style may moderate associations between behavioral anger expression and chronic pain intensity.