====== Tinnitus ====== {{rss>https://pubmed.ncbi.nlm.nih.gov/rss/search/1lwnZtAkZRl8M68L5kqn8sz9Vle7WuAyfQnsQYQDufoMRx8YN-/?limit=15&utm_campaign=pubmed-2&fc=20240823024519}} ===== General information ===== May be either subjective (heard only by patient) or objective (e.g. cranial bruit, can be heard by the examiner as well, usually with a stethoscope placed over the cranium, orbit, or carotid arteries in the neck). Objective tinnitus is almost always due to vascular turbulence (from increased flow or partial obstruction). ---- Tinnitus is the conscious, usually unwanted perception of sound that arises or seems to arise involuntarily in the ear of the affected individual. In most cases there is no genuine physical source of sound. This nonpulsatile tinnitus is caused by a hearing malfunction. ===== Classification ===== see [[Pulsatile tinnitus]]. see [[Non-pulsatile tinnitus]]. ===== Etiology ===== [[Tinnitus Etiology]]. ===== Clinical features ===== Tinnitus may be an accompaniment of sensorineural hearing loss or congenital hearing loss, or it may be observed as a side effect of certain medications (ototoxic tinnitus). Tinnitus is usually a subjective phenomenon, such that it cannot be objectively measured. The condition is often rated clinically on a simple scale from "slight" to "catastrophic" according to the difficulties it imposes, such as interference with sleep, quiet activities, and normal daily activities. ===== Diagnosis ===== Tinnitus and hearing loss in the adult can have profound effects on the quality of life. The imaging workup for tinnitus and hearing loss in adults follows otoscopic exam and audiometry testing. CT and MR imaging have different and often complementary roles in the evaluation of tinnitus and hearing loss depending on the clinical scenario and the suspected underlying cause. Imaging can often identify the cause and evaluate the extent of disease for surgical planning ((Hoang JK, Loevner LA. Evaluation of Tinnitus and Hearing Loss in the Adult. 2020 Feb 15. In: Hodler J, Kubik-Huch RA, von Schulthess GK, editors. Diseases of the Brain, Head and Neck, Spine 2020–2023: Diagnostic Imaging [Internet]. Cham (CH): Springer; 2020. Chapter 15. Available from http://www.ncbi.nlm.nih.gov/books/NBK554328/ PubMed PMID: 32119238. )). ===== Scale ===== [[Tinnitus Handicap Inventory]]. ===== Treatment ===== see [[Tinnitus treatment]]. ===== Case series ===== [[Bayesian model]]s of [[brain function]] such as [[active inference]] and [[predictive coding]] offer a general theoretical framework with which to explain several aspects of normal and disordered brain function. Of particular interest to a study is the potential for such models to explain the pathology of auditory [[phantom perception]], i.e. tinnitus. To test this framework empirically, Hullfish et al., performed an [[fMRI]] experiment on a large clinical sample (n = 75) of the human chronic tinnitus population. The experiment features a within-subject design based on two experimental conditions: subjects were presented with sound stimuli matched to their tinnitus frequency (TF) as well as similar stimuli presented at a control frequency (CF). The responses elicited by these stimuli, as measured using both activity and functional connectivity, were then analyzed both within and between conditions. Given the [[Bayesian]]-brain framework, they hypothesized that TF stimuli will elicit greater activity and/or functional connectivity in areas related to the cognitive and emotional aspects of tinnitus, i.e. tinnitus-related distress. They conversely hypothesize that CF stimuli will elicit greater activity/connectivity in areas related to auditory perception and attention. They discuss this results in the context of this framework and suggest future directions for empirical testing ((Hullfish J, Abenes I, Kovacs S, Sunaert S, De Ridder D, Vanneste S. Functional brain changes in auditory phantom perception evoked by different stimulus frequencies. Neurosci Lett. 2018 Jul 31. pii: S0304-3940(18)30522-6. doi: 10.1016/j.neulet.2018.07.043. [Epub ahead of print] PubMed PMID: 30075284. )). ===== Experimental studies ===== [[Rodent model]]s of [[tinnitus]] are commonly used to study its mechanisms and potential [[treatment]]s. Tinnitus can be identified by changes in the gap-induced prepulse inhibition of the [[acoustic startle reflex]] (GPIAS), most commonly by using [[pressure]] [[detector]]s to measure the [[whole-body startle reflex]] (WBS). Unfortunately, the WBS habituates quickly, the measuring system can introduce mechanical oscillations and the response shows considerable variability. Wallace et al. have instead used a motion tracking system to measure the localized motion of small reflective markers in response to an acoustic startle reflex in [[guinea pigs]] and [[mice]]. For guinea pigs, the pinna had the largest responses both in terms of displacement between pairs of markers and in terms of the speed of the reflex movement. Smaller, but still reliable responses were observed with markers on the thorax, abdomen and back. The peak speed of the pinna reflex was the most sensitive measure for calculating GPIAS in the guinea pig. Recording the pinna reflex in mice proved impractical due to removal of the markers during grooming. However, recordings from their back and tail allowed us to measure the peak speed and the twitch amplitude (area under curve) of reflex responses and both analysis methods showed robust GPIAS. When mice were administered high doses of sodium salicylate, which induces tinnitus in humans, there was a significant reduction in GPIAS, consistent with the presence of tinnitus. Thus, measurement of the peak speed or twitch amplitude of pinna, back and tail markers provides a reliable assessment of tinnitus in rodents ((Wallace MN, Berger JI, Hockley A, Sumner CJ, Akeroyd MA, Palmer AR, McNaughton PA. Identifying tinnitus in mice by tracking the motion of body markers in response to an acoustic startle. Front Neurosci. 2024 Aug 7;18:1452450. doi: 10.3389/fnins.2024.1452450. PMID: 39170684; PMCID: PMC11335616.))