Tinnitus and brain activation: insights from transcranial magnetic stimulation.

Abstract

The mechanisms underlying tinnitus are still not completely elucidated, but advances in neuroimaging and brain stimulation have provided us with new insights. Evidence suggests that tinnitus might actually be generated by central rather than peripheral structures. To illustrate the importance of brain activity changes in the pathology of tinnitus, we report the cases of 2 patients who experienced a recurrence/worsening of their tinnitus after they had undergone treatment for major depression with repetitive transcranial magnetic stimulation. We suggest that the tinnitus in these 2 patients was induced by changes in brain activity resulting from transcranial magnetic stimulation of the prefrontal cortex. We also review the pathophysiology and other aspects of tinnitus, focusing on associated brain reorganization.

Introduction

Tinnitus has been reported to occur in approximately 10 to 15% of adults, including as many as 33% of the elderly population. (l,2) In the United States, tinnitus affects some 30 to 40 million people; approximately 2 to 3 million are severely affected. (l,2) Tinnitus can negatively affect quality of life, sleep, memory, concentration, and mood; these sequelae are debilitating in up to 10% of patients. (3)

Despite the many therapeutic options that are available, a great number of patients continue to experience chronic tinnitus for years. One reason for our inability to cure tinnitus is that its underlying mechanisms have not been completely elucidated. Some authors have proposed that tinnitus is associated with a central rather than peripheral brain dysfunction. (4,5) According to this putative mechanism, peripheral alterations in the cochlear structures still play an important role in triggering tinnitus, but tinnitus does not necessarily represent only end-organ damage; it may also be a consequence of dysfunctional brain activity. For example, Kaltenbach and Afman showed that brain changes in patients with noise-induced tinnitus are still present after the noise is terminated. (6) Therefore, a cortical reorganization in the auditory areas of the brain might sustain chronic tinnitus.

The study of brain alterations in patients with tinnitus might shed light on the pathophysiology of this symptom. Several neuroimaging studies have shown that patterns of brain activation in patients with tinnitus are different from those in healthy controls. (7-10) Although the results of these studies are mixed, they show that patients with tinnitus have increased activity in the temporal cortex. Given that tinnitus might be caused by brain dysfunction, newer techniques of noninvasive brain stimulation--such as transcranial magnetic stimulation (TMS)--might improve our understanding of and perhaps our treatment of this pathology. (11-14)

In this article, we briefly describe 2 cases of tinnitus that were induced by repetitive TMS (rTMS) administered for the treatment of major depression. Thereafter, we discuss the implications of these 2 cases and the possible mechanisms that might explain the development of tinnitus in these patients. We also review the literature on the central mechanisms of tinnitus.

Case reports

Two patients with a history of tinnitus and medication-refractory depression had been participating in a study to evaluate the antidepressant efficacy of rTMS delivered to the dorsolateral prefrontal cortex. Both had been administered rTMS to the left side of the cortex for 10 consecutive days. At each daily session, 1,600 stimuli of 10 Hz rTMS at 90% of motor threshold intensity were delivered in 20 trains of 8 seconds each; there was a 52-second interval between trains.

Patient 1. A 50-year-old left-handed woman had been first evaluated for tinnitus 12 years earlier; she had been symptom-free for 3 years prior to rTMS. Her audiograms and tympanograms had been normal on two previous occasions 15 and 9 years earlier. Her tinnitus began after her second rTMS session, and it …