The Role of the Brainstem in Generating and Modulating Tinnitus

History of Tinnitus Research at the VA National Center for Rehabilitative Auditory Research (NCRAR), 1997-2021: Studies and Key Findings

The Veterans Affairs (VA) Rehabilitation Research & Development (RR&D) National Center for Rehabilitative Auditory Research (NCRAR) was first funded by the RR&D Service in 1997 and has been funded continuously since that time. The overall purpose of the NCRAR is to "improve the quality of life of Veterans and others with hearing and balance problems through clinical research, technology development, and education that leads to better patient care" ( www.ncrar.research.va.gov ). An important component of the research conducted at the NCRAR has been a focus on clinical and rehabilitative aspects of tinnitus. Multiple investigators have received grants to conduct tinnitus research and the present article provides an overview of this research from the NCRAR's inception through 2021.

Associations Between Physiological Correlates of Cochlear Synaptopathy and Tinnitus in a Veteran Population

PURPOSE

Animal models and human temporal bones indicate that noise exposure is a risk factor for cochlear synaptopathy, a possible etiology of tinnitus. Veterans are exposed to high levels of noise during military service. Therefore, synaptopathy may explain the high rates of noise-induced tinnitus among Veterans. Although synaptopathy cannot be directly evaluated in living humans, animal models indicate that several physiological measures are sensitive to synapse loss, including the auditory brainstem response (ABR), the middle ear muscle reflex (MEMR), and the envelope following response (EFR). The purpose of this study was to determine whether tinnitus is associated with reductions in physiological correlates of synaptopathy that parallel animal studies.

METHOD

Participants with normal audiograms were grouped according to Veteran status and tinnitus report (Veterans with tinnitus, Veterans without tinnitus, and non-Veteran controls). The effects of being a Veteran with tinnitus on ABR, MEMR, and EFR measurements were independently modeled using Bayesian regression analysis.

RESULTS

Modeled point estimates of MEMR and EFR magnitude showed reductions for Veterans with tinnitus compared with non-Veterans, with the most evident reduction observed for the EFR. Two different approaches were used to provide context for the Veteran tinnitus effect on the EFR by comparing to age-related reductions in EFR magnitude and synapse numbers observed in previous studies. These analyses suggested that EFR magnitude/synapse counts were reduced in Veterans with tinnitus by roughly the same amount as over 20 years of aging.

CONCLUSION

These findings suggest that cochlear synaptopathy may contribute to tinnitus perception in noise-exposed Veterans.

SUPPLEMENTAL MATERIAL

https://doi.org/10.23641/asha.24347761.

Pilot study on the role of somatic modulation in hyperacusis

BACKGROUND

Hyperacusis is a reduced tolerance to sounds that often co-occurs with tinnitus. Both symptoms have convergent as well as divergent characteristics. Somatic modulation, changes in pitch or loudness during certain movements, is common in patients with a primary complaint of tinnitus. However, thus far, this is not documented in patients with hyperacusis.

OBJECTIVES

This study aimed to examine the influence of somatic manoeuvres on the perception of external sounds in patients with a primary complaint of hyperacusis.

METHODOLOGY

In this prospective cross-sectional pilot study, 18 patients with a primary complaint of hyperacusis were recruited at the Tinnitus Treatment and Research Center Antwerp (TINTRA). While patients listened to a 1 kHz broadband noise of 30 dB sensation level, six neck manoeuvres (flexion, extension, lateroflexion left/right, traction and compression), three jaw manoeuvres (protrusion, laterotrusion left/right) and one placebo manoeuvre (hand on head) were performed. The primary outcome measure was the change in the perception of the presented sound in terms of loudness and intrusiveness between baseline and each modulation measured by a visual analogue scale (VAS).

RESULTS

No overall significant changes were found; however, individual results indicated that five patients presented a clinically relevant change of more than three points out of ten on VAS in terms of hyperacusis after at least one of the executed somatic manoeuvres.

CONCLUSIONS

This pilot study did not demonstrate an overall significant change in hyperacusis after somatic manoeuvres but does not rule out the possibility of somatic modulation in some hyperacusis patients.

TRIAL REGISTRATION

The protocol of this prospective cross-sectional pilot study was registered on clinicaltrials.gov with registration number NCT04693819.

Brainstem evoked auditory potentials in tinnitus: A best-evidence synthesis and meta-analysis

Introduction

Accumulating evidence suggests a role of the brainstem in tinnitus generation and modulation. Several studies in chronic tinnitus patients have reported latency and amplitude changes of the different peaks of the auditory brainstem response, possibly reflecting neural changes or altered activity. The aim of the systematic review was to assess if alterations within the brainstem of chronic tinnitus patients are reflected in short- and middle-latency auditory evoked potentials (AEPs).

Methods

A systematic review was performed and reported according to the PRISMA guidelines. Studies evaluating short- and middle-latency AEPs in tinnitus patients and controls were included. Two independent reviewers conducted the study selection, data extraction, and risk of bias assessment. Meta-analysis was performed using a multivariate meta-analytic model.

Results

Twenty-seven cross-sectional studies were included. Multivariate meta-analysis revealed that in tinnitus patients with normal hearing, significantly longer latencies of auditory brainstem response (ABR) waves I (SMD = 0.66 ms, p < 0.001), III (SMD = 0.43 ms, p < 0.001), and V (SMD = 0.47 ms, p < 0.01) are present. The results regarding possible changes in middle-latency responses (MLRs) and frequency-following responses (FFRs) were inconclusive.

Discussion

The discovered changes in short-latency AEPs reflect alterations at brainstem level in tinnitus patients. More specifically, the prolonged ABR latencies could possibly be explained by high frequency sensorineural hearing loss, or other modulating factors such as cochlear synaptopathy or somatosensory tinnitus generators. The question whether middle-latency AEP changes, representing subcortical level of the auditory pathway, are present in tinnitus still remains unanswered. Future studies should identify and correctly deal with confounding factors, such as age, gender and the presence of somatosensory tinnitus components.

Systematic review registration

https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021243687, PROSPERO [CRD42021243687].

Effectiveness of Dry Needling in Bothersome Chronic Tinnitus in Patients with Myofascial Trigger Points

Introduction  Therapeutic dry needling (DN) is effective in reducing the discomfort of chronic somatosensory tinnitus in patients with myofascial trigger points (MTP)s.

Objective  To evaluate the efficacy of DN in chronic somatosensory tinnitus discomfort in patients with MTP.

Methods  Placebo-controlled paired trial that included 16 patients with a diagnosis of somatosensory chronic tinnitus and with the presence of at least one active or latent MTP. Treatment was performed in two phases: (1) four sessions (one session per week for four consecutive weeks) of placebo DN and (2) four sessions of therapeutic DN with a gap (washout) of 15 days between these phases.

Results  The Tinnitus Handicap Inventory (THI) variable and its emotional domain had a statistically significant reduction in therapeutic DN when compared with placebo DN ( p  = 0.024 and p = 0.011, respectively).

The tinnitus visual analogic scale (VAS) signaled a reduction in tinnitus discomfort when compared with moments before and after therapeutic DN ( p  < 0.05).

Conclusion  The therapeutic DN technique for MTP in patients with chronic tinnitus of somatosensory origin proved effective in reducing symptom discomfort, as measured by the THI (total score) and its emotional domain when compared with placebo DN.

Outcomes at 6 months are related to brain structural and white matter microstructural reorganization in idiopathic tinnitus patients treated with sound therapy

This study aimed to explore brain structural and white matter microstructural reorganization in the early stage of tinnitus and identify brain alterations that contribute to its relief after 6 months of sound therapy. We studied 64 patients with idiopathic tinnitus, including 29 patients who were categorized into an effective group (EG) and 35 who were categorized into an ineffective group (IG) according to the 6-month follow-up improvement of the Tinnitus Handicap Inventory score, along with 63 healthy controls (HCs). All participants underwent structural and diffusion tensor imaging scanning on a 3-T magnetic resonance system. Differences in brain gray/white matter volume and white matter microstructure were evaluated using voxel-based morphometry analysis and tract-based spatial statistics among the three groups. Associations between brain reorganization and the improvement of tinnitus symptoms were also investigated. Compared with EG patients, IG patients experienced a significant gray matter volume decrease in the right middle frontal gyrus (MFG)/right precentral gyrus (PreCG). Meanwhile, both EG and IG patients showed significant changes (decrease or increase) in brain white matter integrity in the auditory-related or nonauditory-related white matter fiber tracts compared with HCs, while EG patients showed decreased axial diffusivity in the bilateral middle cerebellar peduncle (MCP) compared with IG patients. We combined the gray matter change of the MFG/PreCG and the white matter integrity of the bilateral MCP as an imaging indicator to evaluate the patient's prognosis and screen patients before treatment; this approach reached a sensitivity of 77.1% and a specificity of 82.8%. Our study suggests that there was a close relationship between brain reorganization and tinnitus improvement. The right MFG/PreCG and bilateral MCP may be indicators that can be used to predict prognoses in patients with idiopathic tinnitus and may be used to screen patients before sound therapy. These findings may provide new useful information that can lead to a better understanding of the tinnitus mechanism.

Noise: Acoustic Trauma and Tinnitus, the US Military Experience

Tinnitus is commonly experienced by military Service Members and Veterans, especially by the newest generation who served in Iraq and Afghanistan. When patients seek health care for tinnitus, it is important to determine its type, check for comorbid conditions that might be triggering or exacerbating the condition, and to address its functional and psychosocial effects. Otolaryngologists are usually the first health care professional to evaluate a patient with tinnitus, and it is essential to provide appropriate referrals for this high-burden condition. Noise-induced tinnitus is multifaceted; by performing a thorough assessment, appropriate action can be taken to best meet the needs of patients.