Variable Changes in PET Activity Before and After rTMS Treatment for Tinnitus

Objectives/Hypothesis: The objective was to determine whether low-frequency repetitive transcranial magnetic stimulation (rTMS) improves tinnitus by decreasing neural activity in auditory processing regions of the temporal cortex and the utility of positron emission tomography (PET) for targeting treatment. Study Design: Randomized, sham-controlled crossover. Methods: Patients received a five-day course of active and sham 1-Hz rTMS (1800 pulses at 110% of motor threshold) to the temporal cortex, with a week separating active and sham treatment. Visual analogue ratings of tinnitus loudness (VARL) were assessed at baseline and the end of each treatment week; regional brain blood flow (rBBF) and glucose metabolism (via PET) were measured before and after treatment in regions of interest (ROI) beneath the stimulating coil and control sites. Results: The VARL for both ears significantly decreased after active but not sham treatment. Responders comprised 43% of patients, experiencing at least a 33% drop in tinnitus loudness. The site most consistently associated with a positive response was the secondary auditory cortex (Brodmann Area 22) in either hemisphere. PET asymmetries were variable across patients and not always accessible to rTMS. Whereas PET activity decreased significantly beneath the stimulating coil following active treatment, similar changes occurred at control sites and after sham stimulation. Change in tinnitus perception did not correlate significantly with change in PET activity at the treatment site ROI. Conclusions: Active TMS led to a significant reduction in tinnitus loudness, but PET scans failed to support the hypothesis that low-frequency rTMS improves tinnitus by reducing cortical activation at the stimulation site, questioning the utility of PET for targeting rTMS.