Why Does Migraine Improve During a Clinical Trial? Further Results from a Trial of Cervical Manipulation for Migraine

Abstract

Migraine is sensitive to intervention, whether in a treatment situation or in a clinical trial and a placebo effect is often suggested. The influence of a number of non-specific therapeutic ingredients was examined in a recent 6 mo. trial of cervical manipulation for migraine, and results of a 20 mo. follow-up are reported. During the trial, migraine attacks reduced significantly by 28% and reduced a further 19% up to the follow-up period. The possibility of a trial effect, whereby improvement might stem from circumstances of the trial, was dismissed as an explanation for improvement. There was some evidence to suggest that placebo influences made a slight contribution to improvement, with sex, social class and subjects'' optimism about the therapist at the initial treatment being weakly associated with initial improvement. Improvement levels may reflect spontaneous improvement in migraine symptoms. If this possibility proves valid, clinical trials assessing migraine therapies should be designed so as to consider the natural course of migraine. Degree of improvement at follow-up could be predicted clearly from degree of improvement during the treatment phase and from degree of improvement at the end of the trial. This may be important to manipulative therapists who appear to practice without the benefit of valid predictors of response to therapy.