AUDITORY CORTEX STIMULATION FOR TINNITUS SUPPRESSION (2008)

To the Editor: We read the study "Feasibility of Auditory Cortical Stimulation for the Treatment of Tinnitus" (Otol Neurotol 2007;28:1005-12) of Friedland et al. with interest. Surprisingly, their results seem to correlate better with the 1-Hz repetitive transcranial magnetic stimulation (TMS) literature (1,2) than with our cortical stimulation data using implanted electrodes (3,4). In contrast to our results, the authors find more improvement on tinnitus distress than on tinnitus intensity. The difference between these results, and especially why the authors do not find a tinnitus intensity-suppressing effect, requires an explanation. Although an explanation cannot be given at this very moment, 2 considerations can be further explored. First of all, the authors use a different stimulation device and different electrodes. Although this might seem trivial, the electrical stimulation paradigm and current parameters may be critically important to induce tinnitus suppression. Using an electrode with only 2 contacts limits the way the electrodes can be programmed to an extreme. As already mentioned in our first case report (4), and confirmed later in our somewhat larger study population (3), the tinnitus in cortex stimulation via implanted electrodes always recurs in every patient and requires multiple stimulation programs to run alternatingly to prevent tinnitus recurrence. This fits perfectly with the fact that in the study of Friedland et al. study 6 of 8 patients demonstrated a temporary complete suppression of their tinnitus at some point in time during stimulation. Keeping it suppressed might require an electrode with more contacts so more complex programming is possible. A second potentially important difference between the two studies might be the use of preoperative TMS as an inclusion criterium for surgical implantation. In our multidisciplinary TRI tinnitus clinic, approximately 300 patients per year undergo a TMS session. As previously mentioned (5), and in accordance with the TMS literature (1), 40 to 50% of tinnitus patients describe a modification of their tinnitus on transcranial magnetic stimulation, and these results are similar for 1 Hz and high-frequency TMS. Of these 300 patients, approximately 150 describe an immediate, but very short-lasting (order of seconds), effect on high-frequency (>5 Hz) TMS and with a placebo rate approaching 60% (5). This leaves 60 patients who meet our criteria and 240 who do not. Whether TMS is important as a prognostic criterium is not known yet, but if it is, it can also explain differences in outcome. Therefore, a study comparing TMS responders to TMS nonresponders in relationship to the outcome of implanted electrodes seems mandated. Much more clinical research such as this is needed to determine whether auditory cortex stimulation can become a valuable and accepted treatment for intractable tinnitus in the future, and the authors are to be congratulated for their nice work. Dirk De Ridder, M.D., Ph.D. Tomas Menovsky, M.D., Ph.D. Paul van de Heyning, M.D., Ph.D. Multidiscplinary TRI Tinnitus Clinic Antwerp University Hospital Antwerp Edegem, Belgium