Pain expectancy may affect the pain experience in older patients with knee osteoarthritis after genuine (verum) and sham electroacupuncture, according to a study published in the Journal of Pain. Verum and sham acupuncture were associated with distinct brain activity, as assessed by functional magnetic resonance imaging (fMRI).
To examine the mechanisms by which expectancy may modulate analgesia, adults with knee osteoarthritis received verum electroacupuncture (n=21; mean age, 57±7 years) or sham electroacupuncture (n=22; mean age, 59±7 years).
Subjective ratings of pain following thermal stimuli were measured before and after intervention. Pain expectancy was conditioned in 2 ways: by telling participants that acupuncture is only effective on a particular side of the arm (high-expectancy side) and by reducing the heat level after acupuncture to faint or weak on the high-expectancy side, giving participants a profound sense of analgesia. Whole-brain imaging was conducted during the delivery of pain stimuli and during electroacupuncture.
In both sham and verum electroacupuncture groups, statistical analysis revealed an interaction between manipulation of expectancy and subjective ratings of pain (P <.001). Participants in both groups reported improved analgesia on the high-effectiveness side of the arm compared with the other side.
No difference in analgesia effect was reported between verum and sham acupuncture, and participants in both groups reported greater pain relief on the high-expectancy side of the arm and increased pain on the control side of the arm.
For patients who received verum electroacupuncture, fMRI signals indicated that the lateral prefrontal cortex, orbital prefrontal cortex, and insula had increased activity at the time of noxious stimulation of the high-expectancy vs control side of the arm.
In contrast, the sham electroacupuncture group had increased activation in the medial prefrontal cortex and orbital prefrontal cortex during noxious stimulation of the high-expectancy vs control side.
The investigators concluded that “expectancy may work through different pathways based on the treatment modality and pathophysiological state of the person.” They noted that future studies that “include larger cohorts of chronic pain patients and age matched pain-free control subjects that can be directly compared are needed to disentangle the potential confounding effects of aging on these neural responses.”
Gollub RL, Kirsch I, Maleki N, et al. A functional neuroimaging study of expectancy effects on pain response in patients with knee osteoarthritis [published online January 8, 2018]. J Pain. doi: 10.1016/j.jpain.2017.12.260