Research on placebo
analgesia and nocebo
hyperalgesia has primarily included healthy subjects or
acute pain patients, and it is unknown whether these effects can be obtained in ongoing
pain in patients with
chronic pain caused by an identifiable nerve injury. Eighteen patients with postthoracotomy
neuropathic pain were exposed to placebo and nocebo manipulations, in which they received open and hidden administrations of
pain-relieving (
lidocaine) or
pain-inducing (
capsaicin) treatment controlled for the natural history of
pain. Immediately after the open administration, patients rated their expected
pain levels on a mechanical visual analogue scale (M-VAS). They also reported their emotional feelings via a quantitative/qualitative experiential method. Subsequently, patients rated their ongoing
pain levels on the M-VAS and underwent quantitative sensory testing of evoked
pain (brush, pinprick, area of
hyperalgesia, wind-up-like
pain). There was a significant placebo effect on both ongoing (P=.009 to .019) and evoked
neuropathic pain (P=.0005 to .053). Expected
pain levels accounted for significant amounts of the variance in ongoing (53.4%) and evoked
pain (up to 34.5%) after the open
lidocaine administration. Furthermore, patients reported high levels of positive and low levels of negative emotional feelings in the placebo condition compared with the nocebo condition (P⩽.001).
Pain increases during nocebo were nonsignificant (P=.394 to 1.000). To our knowledge, this is the first study to demonstrate placebo effects in ongoing
neuropathic pain. It provides further evidence for placebo-induced reduction in
hyperalgesia and suggests that patients' expectations coexist with emotional feelings about treatments.