In October’s issue of Science a study showed a physiological response to a placebo topical analgesia. This article addresses the study design and findings, and concludes with its relation to chiropractic.

The study contained a population of 13 subjects, who were told that they were part of a trial to test the efficacy of a new pain killer cream. First patients were exposed to a painful heat source on their arm, and then researchers applied the ‘control cream’ (which was the same cream as the supposed pain-reducing cream). The patients’ pain ratings were then recorded. Next, researchers repeated the experiment but this time with the pain reducing cream, however, after administering the cream they lowered the temperature of the heat source without informing the patient. Therefore, the patients felt less pain with the pain-reducing cream.

In the second phase of the study, researchers performed functional MRIs at the C5-C6 junction on the patient while exposing the arm to a painful heat stimulus.  One part of the forearm was covered with the ‘control’ and the other with the ‘pain-reducing’ cream; each spot was exposed 25 times and at the same heat. The placebo effect took hold, and patients reported an average of 26% less pain in the analgesic arm.

Of course, proving the placebo effect is nothing new. What is amazing is that the fMRIs revealed that the ipsilateral dorsal horns lit up when the ‘control’ was exposed to the heat, but did not equally activate during the ‘pain-killer’ trials.

So what may this mean to our profession?

1. This study can be looked at in a reverse placebo manner. When a patient is at their doctor, and they are told to go to a DO, but they haven’t had relief in the past with DO’s (even if it was for a different condition), the patients ability to improve under a DO would be greatly decreased, as compared to a chiropractor administering the exact same treatment. The patient may be actively not allowing the natural placebo effect to apply.

2. This study supports the top-down effect gate-theory, and thus may lend some credence to upper cervical practioners. It is wholly possible that a subluxation, and its effects on the spinal cord, may disrupt the descending pain pathways. If the pathway’s function is altered, the brain may be unable to properly block the ascending pain signals. Of course, an adjustment at any level of the spine should affect this process for pain generated at or below the segment, but I mention upper cervicals because if there is a disrupting dysfunction at C0-C1, the whole system will be affected, all the way to your toes.

Now I know the suggestion above is not new to upper cervical practioners, but for the rest of us, it can help to see why a patient with fibromyalgia, psychosomatic pain, or other chronic pain syndromes may be benefited by a seemingly unrelated subluxation/dysfunction at the C/T junction for example, even in the absence of a mechanical dysfunction.

Of course, under that theory one would have to ask why the descending pathways are affected, and not the ascending pathways. I honestly do not know as the tracts are varying in many factors; although their locations may provide a slight clue as the descending pathway is somewhat more centrally located in the spinal cord. If the stress upon the spine is in rotary fashion, the central tissue would be subjected to a higher degree of stress. This theory would support both the classical ‘bone out of place’ model (bone shift to the left, applying a physical stressor), and the ‘restricted joint’ model (superior or inferior joints applying compensation stresses due to the restricted joint).

3. This shows the placebo effect is not just in the mind, its in the spine…

4. If we are smart, and can find the funding, this study may provide our profession a platform for demonstrating real physiological and neural effects from adjustments. Of course, it can also be used against us if the trials are poorly designed…

Direct Evidence for Spinal Cord Involvement in Placebo Analgesia

Science 16 October 2009:
Vol. 326. no. 5951, p. 404