Saturday, September 4, 2010

Nasty Nocebo Effects Make Pain Worse

Briefly Noted Cautioning patients in advance about procedural pain — eg, “This may sting a bit” — could do more harm than good. German researchers found such statements can invoke a nocebo effect, an evil twin of the placebo effect, which can last for many days.

It is generally accepted that an acutely painful experience can be influenced by context information, such as the setting or practitioner statements, which shape a patient’s expectations and modulate attention, arousal, stress, and mood. Rather than invoking a placebo effect that diminishes pain, just the opposite may occur; that is, a nocebo effect that exacerbates pain. However, little is known about the nature, duration, and extent of this nocebo effect, particularly regarding negative expectations.

During an experiment lasting 8 consecutive days and using a brief, daily, standardized painful heat stimulus, 38 healthy volunteers were randomly assigned to one of 2 groups: the first group was told that the investigators expected the pain intensity to increase over time (Context Group); the second group was not given any information at all (Control Group) [Rodriguez-Raecke et al. 2010]. All participants rated the intensity of the pain stimulus on a visual analog scale. Pain ratings in the Control Group diminished over time as they got used to the stimulus; whereas, the Context Group reported greater pain at the outset that did not change during the 8 days of the experiment.

COMMENTARY: On the surface, this small-scale experiment seems to merely confirm the powers of negative suggestion on patients’ reactions to pain. Surprisingly, however, the research also suggests that a negative context not only has a nocebo effect on immediate pain response but can affect negative perceptions of pain in the future — in this case, lasting a full week. For those interested, functional neuroimaging data were collected as part of the experiment and showed a difference between the two groups in the right parietal operculum. This is a brain region containing the secondary somatosensory cortex (S2) that influences pain perception, and it also has interconnections with limbic areas affecting attention, arousal, and mood in response to pain. As we noted in a blogpost last April [here], environmental cues such as pain-related images or words can fire-up limbic-brain centers that serve as a repository of painful memories, and the results of this experiment appear to support that. Caveat orator — speaker beware and choose your words carefully may be wise advice for healthcare providers in communicating with patients in pain.

REFERENCE: Rodriguez-Raecke R, Doganci B, Breimhorst M, et al. Insular Cortex Activity Is Associated with Effects of Negative Expectation on Nociceptive Long-Term Habituation. J Neuroscience. 2010;30(34):11363-11368 [abstract here].