Parameters predicting TMS treatment response go undetected

Researchers have been unable to find factors that predict the efficacy of transcranial magnetic stimulation (TMS) in the treatment of major depression.

"Either study sizes and numbers and designs are insufficient to afford the power necessary to detect such predictors or TMS has a nonspecific effect on depression that is not influenced by study parameters," say Lucie Herrmann (University of Edinburgh, UK) and colleagues.

The researchers carried out a meta-analysis on 33 studies identified through a literature review of published studies.

The results showed that active TMS treatment was more effective than sham treatment in reducing symptoms of depression, with a large effect size of 0.71.

However, variability in study parameters such as age, depression type, and chronicity, presence of psychotic symptoms, duration and severity of illness, number of repetitive (r)TMS trains delivered per session, inter-train interval, and number of stimuli in each stimulation train meant that no single parameter was shown to be a predictor of outcome.

"From the results of the present analysis, it appears that there are no variables that clearly predict rTMS efficacy," the researchers write in the Journal of Clinical Psychiatry.

The team notes, however, that mean effect sizes were reduced, although not significantly, in studies in which stimulation intensity was below 90% of motor threshold and new medication was started within 7 days before or up to 7 days after the start of TMS.

"Until the optimal treatment parameters are found, rTMS remains an experimental approach for the treatment of depression," say Hermmann et al.

"More knowledge regarding the characteristics of patients who benefit from this treatment and the size and persistence of clinical effects is much needed."

The researchers therefore call for large, rigorously controlled studies so that definitive judgments on predictors of TMS treatment outcome can be made.

J Clin Psychiatry 2006; 67: 1870-1876