Sham or real--post hoc estimation of stimulation condition in a randomized transcranial magnetic stimulation trial

Selecting a suitable sham condition within the frame of repetitive transcranial magnetic stimulation (rTMS) treatment trials is a central issue. On the one hand, the ideal sham condition should not have a real stimulation effect; on the other hand, it should not be recognized as sham by patients, particularly when considering that real stimulation conditions come along with rTMS specific side effects. Within the course of a multi-centre trial assessing the antidepressant effects of rTMS, patients were randomized to sham or real stimulation, in both cases using a standard stimulation coil. In one centre, patients (n=33) were asked about their impression whether they received the sham or the real treatment, and if they would recommend the treatment to others. 29 patients returned the questionnaires and were included into the analysis. From 15 subjects with real stimulation, 11 suggested to have obtained real, and 4 to have obtained sham. From 14 sham stimulated subjects, 9 suggested to have obtained the real condition and 5 to have been sham stimulated. This difference was not significant (p=0.60, chi square test). In addition, the major part of patients in both stimulation conditions would recommend rTMS to others. In both conditions, real and sham, the majority of subjects believed to have obtained the real condition. This implies suitability of the sham condition used since subjects appeared not to be able to identify the condition. The results imply the feasibility of a valid sham condition with a "real" coil.