A new study tested the efficacy of chiropractic spinal manipulative therapy (CSMT) for migraine. It was designed as a three-armed, single-blinded, placebo -controlled RCT of 17 months duration including 104 migraineurs with at least one migraine attack per month. Active treatment consisted of CSMT (group 1) and the placebo was a sham push manoeuvre of the lateral edge of the scapula and/or the gluteal region (group 2). The control group continued their usual pharmacological management (group 3).
The RCT began with a one-month run-in followed by three months intervention. The outcome measures were quantified at the end of the intervention and at 3, 6 and 12 months of follow-up. The primary end-point was the number of migraine days per month. Secondary end-points were migraine duration, migraine intensity and headache index, and medicine consumption.
The results show that migraine days were significantly reduced within all three groups from baseline to post-treatment (P < 0.001). The effect continued in the CSMT and placebo groups at all follow-up time points (groups 1 and 2), whereas the control group (group 3) returned to baseline. The reduction in migraine days was not significantly different between the groups. Migraine duration and headache index were reduced significantly more in the CSMT than in group 3 towards the end of follow-up. Adverse events were few, mild and transient. Blinding was strongly sustained throughout the RCT.
The authors concluded that it is possible to conduct a manual-therapy RCT with concealed placebo. The effect of CSMT observed in our study is probably due to a placebo response.
Chiropractors often cite clinical trials which suggest that CSMT might be effective. The effects sizes are rarely impressive, and it is tempting to suspect that the outcomes are mostly due to bias. Chiropractors, of course, deny such an explanation. Yet, to me, it seems fairly obvious: trials of CSMT are not blind, and therefore the expectation of the patient is likely to have major influence on the outcome.
Because of this phenomenon (and several others, of course), sceptics are usually unconvinced of the value of chiropractic. Chiropractors often respond by claiming that blind studies of physical intervention such as CSMT are not possible. This, however, is clearly not true; there have been several trials that employed sham treatments which adequately mimic CSMT. As these frequently fail to show what chiropractors had hoped, the methodology is intensely disliked by chiropractors.
The above study is yet another trial that adequately controls for patients’ expectation, and it shows that the apparent efficacy of CSMT disappears when this source of bias is properly accounted for. To me, such findings make a lot of sense, and I suspect that most, if not all the ‘positive’ studies of CSMT would turn out to be false positive, once such residual bias is eliminated.