The neuroanatomical hallmarks of chronic tinnitus in comorbidity with pure-tone hearing loss

Prevalence of tinnitus following non-blast related traumatic brain injury: a systematic review of literature

OBJECTIVES

To establish the prevalence of tinnitus in adults who have sustained non-blast related traumatic brain injury (TBI), as well as the prevalence of tinnitus following TBI in the absence of hearing loss.

METHODS

A systematic search was carried out using MEDLINE, EMBASE, PsycINFO, CINAHL from January 1st 1990 to August 14th 2023. TBI, tinnitus and auditory findings were extracted from all eligible studies, and a descriptive synthesis performed. This systematic review was registered with PROSPERO (Registration number: CRD42022377637).

RESULTS

Based on the Oxford Centre of Evidence-Based Medicine (OCEBM) (2011) criteria, the highest quality evidence identified was at Level 2b, with the bulk of the included studies predominantly populating the lower evidence tiers. While there was a substantial variability in the methods used to establish and report the presence of tinnitus, its occurrence following TBI was evident in adults with and without hearing loss.

CONCLUSION

The need for prospective, longitudinal research into tinnitus following non-blast related TBI is evident. Such comprehensive studies hold the potential to inform and enhance the clinical diagnosis and management of this patient population.

What is the role of the hippocampus and parahippocampal gyrus in the persistence of tinnitus?

The hippocampus and parahippocampal gyrus have been implicated as part of a tinnitus network by a number of studies. These structures are usually considered in the context of a "limbic system," a concept typically invoked to explain the emotional response to tinnitus. Despite this common framing, it is not apparent from current literature that this is necessarily the main functional role of these structures in persistent tinnitus. Here, we highlight a different role that encompasses their most commonly implicated functional position within the brain-that is, as a memory system. We consider tinnitus as an auditory object that is held in memory, which may be made persistent by associated activity from the hippocampus and parahippocampal gyrus. Evidence from animal and human studies implicating these structures in tinnitus is reviewed and used as an anchor for this hypothesis. We highlight the potential for the hippocampus/parahippocampal gyrus to facilitate maintenance of the memory of the tinnitus percept via communication with auditory cortex, rather than (or in addition to) mediating emotional responses to this percept.

A Systematic Review on the Genetic Contribution to Tinnitus

PURPOSE

To assess the available evidence to support a genetic contribution and define the role of common and rare variants in tinnitus.

METHODS

After a systematic search and quality assessment, 31 records including 383,063 patients were selected (14 epidemiological studies and 17 genetic association studies). General information on the sample size, age, sex, tinnitus prevalence, severe tinnitus distribution, and sensorineural hearing loss was retrieved. Studies that did not include data on hearing assessment were excluded. Relative frequencies were used for qualitative variables to compare different studies and to obtain average values. Genetic variants and genes were listed and clustered according to their potential role in tinnitus development.

RESULTS

The average prevalence of tinnitus estimated from population-based studies was 26.3% for any tinnitus, and 20% of patients with tinnitus reported it as an annoying symptom. One study has reported population-specific differences in the prevalence of tinnitus, the white ancestry being the population with a higher prevalence. Genome-wide association studies have identified and replicated two common variants in the Chinese population (rs2846071; rs4149577) in the intron of TNFRSF1A, associated with noise-induced tinnitus. Moreover, gene burden analyses in sequencing data from Spanish and Swede patients with severe tinnitus have identified and replicated ANK2, AKAP9, and TSC2 genes.

CONCLUSIONS

The genetic contribution to tinnitus is starting to be revealed and it shows population-specific effects in European and Asian populations. The common allelic variants associated with tinnitus that showed replication are associated with noise-induced tinnitus. Although severe tinnitus has been associated with rare variants with large effect, their role on hearing or hyperacusis has not been established.