Electrical Stimulation to Treat Tinnitus

Early data on stimulation of Heschl’s gyrus are promising, but more research is needed

Direct electrical stimulation of the auditory cortex to relieve symptoms of severe tinnitus has been successfully demonstrated in two patients by Michael Seidman, MD, Director, of Otologic/Neurotologic Surgery in the Department of Otolaryngology-Head and Neck Surgery at the Henry Ford Health System in West Bloomfield, Mich.

Currently there is no cure for tinnitus, which affects nearly 50 million Americans. Of these, about 3% to 4% are severely debilitated, with none of the conventional and alternative types of therapy able to relieve the aberrant noise and sounds characteristic of the condition.

For those patients who have failed conventional management, Dr. Seidman believes that electrical stimulation of the auditory cortex could potentially be an option to treat intractable tinnitus.

In his procedure, two patients, a 50-year-old male and a 40-year-old female with debilitating tinnitus refractory to conventional therapies, were evaluated with validated questionnaires, psychoacoustic measures, magnetoencephalography (MEG), and functional magnetic resonance imaging (fMRI). The male’s hyperexcitable area of Heschl’s gyrus was implanted with a pisces quadripolar electrode; the female was implanted with a four contact electrode. Following the procedures, the male experienced near elimination of tinnitus while the female patient noted a 30% to 35% improvement.

Dr. Seidman presented his findings formally at the 2005 Combined Otolaryngological Spring Meeting in Boca Raton, Fla., and informally with updates at the April International Otology-Audiology Spring Conference in Shanghai, China, and the September International Tinnitus Forum Meeting in Los Angeles, Calif.

The auditory cortex may not be the only site for electrical stimulation.

Reaction from the Field

Following the Los Angeles program, well-known tinnitus researcher Abraham Shulman, MD, Professor Emeritus at SUNY-Downstate in Brooklyn, NY, and Director of Otology and Neurotology at the Martha Entenmann Tinnitus Research Center in Forest Hills, NY, noted in an editorial that notwithstanding that the study was limited to two single cases, the report was exciting.

In an interview with ENToday, Dr. Shulman said Dr. Seidman is to be congratulated for his effort and that the procedure was a significant step forward, but it is premature at this time to think of this as a treatment for tinnitus. The procedure is an ongoing research project. Its significance for tinnitus relief will be determined by the long-term clinical course of the tinnitus, as reported by patients following the procedure.

He also indicated that for success of the procedure in achieving tinnitus relief, patient selection will be critical and the reported tinnitus relief will most likely be individual and variable.

James Kaltenbach, PhD, Professor of Otolaryngology at Wayne State University in Detroit, Mich., had similar comments: This is the first study suggesting that direct electrical stimulation of the auditory cortex may be an effective approach to the suppression of tinnitus. Further study needs to be conducted to verify these promising findings in a larger number of patients.

History of Electrical Stimulation for Tinnitus

Although electrical stimulation as a potential treatment for tinnitus has been tried with mixed results since the 1800s, the type of stimulation used and the location of delivery has varied. The earliest experiments involved anodal direct current, which suppressed some cases of tinnitus but did not result in useful clinical application, according to Jay T. Rubinstein, MD, PhD, and Richard S. Tyler, PhD, in their chapter Electrical Suppression of Tinnitus, in the textbook Tinnitus (Decker 2004). The authors added that only specific frequencies and intensities of alternating current, such as those used in cochlear implants, are safe for chronic stimulation.

Regarding sites for electrical stimulation, Drs. Rubinstein and Tyler mentioned the external auditory canal, auricle, zygoma, tragus, mastoid, and Eustachian tube orifice.

I think most people have suspected that there is a cortical representation for some forms of tinnitus. It is fairly clear that the auditory cortex plays a role in audition and the perception of auditory signals, Dr. Seidman said. Also, it is tonotopically mapped, meaning there are areas within the auditory cortex that map to a specific frequency…so it made sense.

He added that the auditory cortex may not play a role in everybody’s tinnitus. But we think it probably does because it affects your perception of that tinnitus.

Assessing the Patient’s Response

In the assessment portion of his study, Dr. Seidman used conventional pure tone audiometry and speech recognition testing. In addition, the patients were asked to complete a battery of self-assessment questionnaires including the Tinnitus Handicap Inventory, the Tinnitus Reaction Questionnaire, the Beck Depression Inventory, and the Modified Somatic Perception Questionnaire.

Psychoacoustic measures were taken in a sound-treated booth as a continuous tone was presented below threshold and increased until the patient indicated that the tone was equivalent in loudness to the tinnitus. To obtain minimum masking levels, white noise was delivered and measured, and residual inhibition was calculated. The fMRI study allowed for a general localization of the anatomical landmarks within the Heschl’s gyrus of the auditory cortex and the MEG showed a precise area of cortical activation arising from the auditory and visual inputs. Auditory evoked responses were also recorded.

The male patient in the study, identified as RP, had a 20-month history of intractable subjective tinnitus, most likely due to bilateral, symmetric, mild, high-frequency sensorineural hearing loss. Following the surgery, RP perceived a rapid reduction in tinnitus. A series of single-blinded extra-operative tests ruled out a placebo effect. Three months after the surgery, RP reported that his tinnitus was essentially gone when the electrode was active, with the residual inhibition lasting for several days after turning the device off.

The second patient, identified as MV, had been left with a left-sided hearing deficit following a motor vehicle accident in 1997. Her tinnitus was associated with short lasting bouts of otalgia and spells of vertigo. Multiple medical and masking treatments had been unsuccessful in alleviating her tinnitus, as was a procedure providing extradural stimulation. Following the new procedure, MV experienced a 30% to 35% reduction in her tinnitus.

Next Step: Refining the Technique

Currently, Dr. Seidman has 32 people on a waiting list for the surgery and he expects to perform five more procedures within the near future. Because a drawback to the surgery is its invasive nature, requiring the removal of an entire bone flap, Dr. Seidman plans to perform his next operation with a minimally invasive procedure utilizing a 9 mm burr hole.

In addition, he noted that the auditory cortex may not be the only site for electrical stimulation.

You may be able to target areas other than the auditory cortex that aren’t even in the auditory system, he commented. The obvious ones are the cochlea, the cochlear nerve, the inferior cochlear nucleus, the superior cochlear nucleus, the dorsal and ventral cochlear nuclei, and the medial geniculate body. There are different areas in the auditory pathway that you can target and have an effect. But beyond that, you can affect the places that mediate a response to a severely annoying symptom. For example, the amygdala and the hippocampus.

You may be able to target areas other than the auditory cortex that aren’t even in the auditory system. – -Michael Seidman, MD

Along this line, Dr. Seidman is collaborating with Dirk de Ridder, MD, PhD, Professor of Neurosurgery at the University of Antwerp in Belgium, who has done electrical stimulation procedures similar to Dr. Seidman’s. The two plan to implant an electrical probe into the hippocampus of patients with severe tinnitus.

The idea is to alter their reaction to the tinnitus, so it won’t bother them anymore, he said. We hope to do this within the next year.

Other Research Fronts

In addition to Drs. Seidman and de Ridder, another physician researcher studying electrical stimulation of the auditory cortex for tinnitus is Brian Kopell, MD, of the Medical College of Wisconsin in Milwaukee, who is enrolling patients in a clinical trial. A group at the Oregon Hearing Research Center at Oregon Health Science University in Portland is investigating the use of deep brain stimulation for tinnitus.

Also, Dr. Rubinstein, who is Professor of Otolaryngology and Bioengineering and the Virginia Merrill Bloedel Professor and Director of the Virginia Merrill Bloedel Research Center at the University of Washington in Seattle, is trying new methods of cochlear implantation to treat tinnitus, with success in a small number of patients. Currently, he is using short cochlear insert electrodes that may suppress tinnitus while causing no damage to the inner ear.

While it is too soon to tell if any of these approaches will offer an effective management tool for tinnitus, the experts agree that electrical stimulation offers exciting possibilities for treating persistent, debilitating cases.

©2006 The Triological Society