Multiple electrostimulation treatments to the promontory for tinnitus.

OBJECTIVES: To assess the safety and efficacy of multiple sessions of electrostimulation by a transtympanic needle electrode on the promontory for tinnitus relief. STUDY DESIGN: Prospective open, unblinded, uncontrolled clinical trial. SETTING: Tertiary academic referral center. PATIENTS: Ten patients (8 male and 2 female subjects), mean age 50.1 ± 12 years (range, 34-67) with severe unilateral tinnitus completed all stages of the study. Patients with tinnitus duration between 6 months to 3 years were included. INTERVENTION: The patients underwent 3 consecutive 30-minute sessions, every other day, of biphasic, charge balanced electrostimulation pulses to the promontory delivered by a transtympanic needle electrode. MAIN OUTCOME MEASURES: 1) Tinnitus loudness reported by visual analog scale (VAS) between 1 and 10, at baseline, before and after each treatment, and 1, 2, 3, and 4 weeks after the last treatment. 2) Tinnitus Handicap Inventory (THI) questionnaire at baseline and 4 weeks after treatment. 3) Basic audiometry and tinnitus specific tests such as minimum masking level, tinnitus loudness, and pitch. RESULTS: No long-term adverse safety outcomes were noted in physical examination or audiologic evaluation. VAS levels decreased by ≥2 levels in 5 patients (50%) and returned to baseline 4 weeks after treatment. The VAS decrease was found significant (p = 0.048) in those patients. A statistically significant decrease in THI score was noted 4 weeks after treatment. Tinnitus specific tests at that time were unchanged from baseline. CONCLUSION: Multiple sessions of electrostimulation to the promontory seem to be safe and may be beneficial for some tinnitus patients. Further clinical trials are warranted.

Cochlear activation at low sound intensities by a fluid pathway.

In order to assess the mechanisms responsible for cochlear activation at low sound intensities, a semi-circular canal was fenestrated in fat sand rats, and in other experiments a hole was made in the bone over the scala vestibuli of the first turn of the guinea-pig cochlea. Such holes, which expose the cochlear fluids to air, provide a sound pathway out of the cochlea which is of lower impedance than that through the round window. This should attenuate the pressure difference across the cochlear partition and thereby reduce the driving force for the base-to-apex traveling wave along the basilar membrane. The thresholds of the auditory nerve brainstem evoked responses (ABR) and of the cochlear microphonic potentials were not affected in the fenestration experiments. In addition, holes in the scala vestibuli of the first turn did not cause ABR threshold elevations. These results contribute further evidence that at low sound intensities the outer hair cells are probably not activated by a base-to-apex traveling wave along the basilar membrane. Instead it is possible that they are excited directly by the alternating condensation/rarefaction fluid pressures induced by the vibrations of the stapes footplate. The activated outer hair cells would then cause the localized basilar membrane movement.

Lateralization during the Weber test: animal experiments.

OBJECTIVES/HYPOTHESIS: The objective of this study were to present an assessment of a new theory to explain lateralization during the Weber test using an animal model. This theory is based on the discovery that a major pathway in bone conduction stimulation to the inner ear is through the skull contents (probably the cerebrospinal fluid [CSF]). The placement of a bone vibrator or tuning fork on the skull excites the inner ear by the classic osseous pathway and by the suggested CSF pathway. We assume that there is a phase difference between the stimulation mediated by the ossicular chain (inertial and occlusion mechanisms) and the one mediated by the CSF. The presence of a conductive pathology will decrease the magnitude of the sound energy mediated by the ossicular chain. Thus, the out-of-phase signal arriving through the bony pathways will be decreased, hence increasing the resultant sound intensity stimulating the cochlea. STUDY DESIGN: Prospective animal study. METHODS: The experiment was performed on 10 fat sand rats, which had undergone unilateral cochleostomy and a small craniotomy. The auditory nerve brainstem response (ABR) thresholds were measured to air-conducted stimulation, to stimulation with the bone vibrator applied to the skull, and to stimulation with the bone vibrator applied directly to the brain through the craniotomy. The ossicular chain of the second ear was then fixed to the middle ear walls with cyanoacrylate glue to induce a conductive hearing loss. The ABR thresholds to the same three stimuli were then measured again. RESULTS: After ossicular chain fixation, the ABR threshold to air-conducted stimulation increased, to bone vibrator stimulation on the bone decreased (hearing improvement), and to bone vibrator stimulation directly on the brain remained unchanged. CONCLUSIONS: This experiment confirms the proposed theory. During clinical bone conduction stimulation, there is a phase difference between sound energy reaching the inner ear through the middle ear ossicles and from the CSF. A middle ear conductive pathology removes one of these components, thus increasing the effective sound intensity in the affected ear. On the other hand, when the bone vibrator is applied on the brain, the inner ear is stimulated only through the CSF, so ossicular chain fixation does not change the ABR threshold. Moreover, this study proves that lateralization during the Weber phenomenon is the result, at least in part, of an intensity difference between sound energy reaching the two cochleae.