Repetitive transcranial magnetic stimulation for the treatment of chronic subjective tinnitus: Optimization of treatment effects

Subjective tinnitus is a highly prevalent and for many patients very debilitating condition for which there is still no cure. As tinnitus has been shown to be associated with changes of neural activity in different areas of the cortex, repetitive transcranial magnetic stimulation (rTMS) has been used as a treatment tool in order to interfere with these changes. Up to now, treatment success is limited and strategies to enhance treatment effects are clearly needed. The three studies of this cumulative dissertation address the question how rTMS treatment of patients suffering from chronic subjective tinnitus can be optimized. Study 1 tested whether treatment response was associated with grey matter (GM) changes and whether pre-treatment GM volume might be a potential predictor for treatment success. Although transient GM changes in the insulae and the bilateral inferior frontal cortex were observed, these changes were not correlated to treatment outcome. It was shown, however, that GM volume in the frontal cortex and the lingual gyrus might be possible predictors for treatment response. While traditionally, rTMS targeted the auditory cortex of tinnitus patients, study 2 and study 3 examined a new protocol which stimulated three sites successively in order to better interfere with cortical networks involved in tinnitus pathophysiology: the left dorsolateral prefrontal cortex and the left and right temporoparietal cortices. Study 2 was a pilot study which tested the new protocol in a one-arm open label study and compared the results with a historical control group of patients receiving traditional single-site stimulation. The results suggested that the triple-site protocol might show better long-term effects. As a consequence, the new protocol was explored in more detail in study 3 in order to replicate the result in a randomized controlled parallel group trial. In this study, the superiority of the multisite protocol was only seen on a descriptive but not on a statistical significant level. In a concluding discussion, the methods used in this work and future approaches for the enhancement of rTMS treatment effects are discussed