Review Article Hearing Disorders and Sensorineural · PDF fileReview Article Hearing Disorders...
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Review ArticleHearing Disorders and Sensorineural Aging
Alessandra Fioretti,1 Otello Poli,2 Theodoros Varakliotis,3 and Alberto Eibenstein1,3
1 Tinnitus Center European Hospital, Via Portuense 700, 00149 Rome, Italy2 Neurology and Neurophysiopathology Unit European Hospital, Via Portuense 700, 00149 Rome, Italy3 Department of Biotechnological and Applied Clinical Sciences, University of LAquila, 67100 LAquila, Italy
Correspondence should be addressed to Alessandra Fioretti; email@example.com
Received 22 July 2013; Revised 29 September 2013; Accepted 31 October 2013; Published 22 January 2014
Academic Editor: Martin J. Sadowski
Copyright 2014 Alessandra Fioretti et al. This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.
The physiological age-related hearing loss is defined as presbycusis and it is characterized by reduced hearing sensitivity andproblems in understanding spoken language especially in a noisy environment. In elderly the reduced speech recognition isgenerally caused by a reduction of the cochlear cells in the organ of Corti and degeneration of the central auditory pathways. In orderto have a completemanagement strategy of central and peripheral presbycusis the diagnostic evaluation should include clinical ENTexamination, standard audiological tests, and tests of central auditory function. Treatment should include not only the appropriateinstruments for peripheral compensation but also auditory rehabilitative training and counseling to prevent social isolation andloss of autonomy. Other common hearing disorders in elderly are tinnitus and hyperacusis which are often undervalued. Tinnitusis characterized by the perception of a phantom sound due to abnormal auditory perception. Hyperacusis is defined as a reducedtolerance to ordinary environmental sounds. Furthermore auditory, visual, nociceptive, andproprioceptive systemsmaybe involvedtogether in a possible context of sensorineural aging. The aim of this review is to underline the presence of hearing disorders liketinnitus and hyperacusis which in many cases coexist with hearing loss in elderly.
Hearing loss affects approximately one-third of adults over 60years .
Typical changes in presbycusis start with a hearing losson high frequencies with a progression toward the lowerfrequencies and a deterioration of the hearing threshold .Many factors contribute to presbycusis like morphologicalalterations in the stria vascularis, loss of hair cells in thecochlea, and degeneration of the central auditory pathway[3, 4], depending on a genetic basis, smoking, vascularchanges, metabolic disorders, and environmental exposure tonoise . However, the originating signals that trigger thesemechanisms remain unclear. Changes within the cochleaare responsible for age-related hearing loss typically linkedwith low speech understanding especially in presence ofcompeting sound sources. The phenomenon of low speechunderstanding in elderly is related to modifications in centralbrain processes.
Associations between hearing loss and blood lipids inolder adults have been studied for many years. Currentlythe association is considered controversial . Despite somelimitations in data collection methods, interesting findingswere proposed by Verschuur et al. about the significantassociation between hearing loss in older people and higherlevels of four markers of inflammation: white blood cellcount, neutrophil count, IL-6, and C-reactive protein .
Central auditory disorders are common in neurodegen-erative diseases, including dementia and Alzheimers disease. In these cases the evaluation of auditory threshold and theidentification and characterization of associated symptomslike tinnitus or hyperacusis can be difficult and objectivemea-sures are requested. Recognition of tinnitus and decreasedsound tolerance in elderlymust be also considered because inmany cases they are still undervalued or confused especiallywith somatosounds, epilepsy, or psychotic illusions.
Tinnitus is defined as a perception of a sound withoutan external acoustic source. It can be persistent, intermittent,
Hindawi Publishing CorporationJournal of GeriatricsVolume 2014, Article ID 602909, 6 pageshttp://dx.doi.org/10.1155/2014/602909
2 Journal of Geriatrics
or throbbing, depending on the cause. It is important todistinguish between subjective and objective tinnitus. Subjec-tive tinnitus (95% of cases) has a neurophysiological originwhereas objective tinnitus (5% of cases) can be generatedfrom vascular, muscular, or respiratory sources and alsofrom the temporomandibular joint. Another classificationof tinnitus is in pulsatile and not pulsatile. There are manyhypotheses to explain the origin of tinnitus even if none hasyet been proven.Many conditions are associatedwith tinnitusand they are reported in Table 1. Tinnitus becomes moreprevalent in association with aging and hearing loss, withan estimated prevalence of 1218% over the age of 60 years.
Audiologists describe decreased sound tolerance usingthe terms hyperacusis, phonophobia, misophonia, andrecruitment. Hyperacusis is defined as unusual toleranceto ordinary environmental sounds  or as consistentlyexaggerated or inappropriate responses to sounds that areneither threatening nor uncomfortably loud to typical per-son . The prevalence of chronic hyperacusis in thegeneral population aged 5179 years has been estimated asup to 9% . It is widely noted that patients suffering withtinnitus also present with hyperacusis in 4079%of cases . Instead, in patients with hyperacusis, tinnitus has beenreported in 86% .
The mechanisms of hyperacusis generation could involvea peripheral origin, principally the cochlea, the central audi-tory pathways, endogen endorphins, or central disorders. Inthe hypothesis of a peripheral origin, the hyperexcitability ofthe outer hair cells (OHC) of the cochlea would overstimulatethe action of inner hair cells (IHC) so a moderate soundmay be amplified and will be annoying. Distortion-productotoacoustic emissions (DPOAEs) are an objective indicatorof normally functioning OHC. DPOAEs in some patientswith hyperacusis show increased values . The centralauditory origin may be related to the impairment of thelateral olivocochlear bundle (LOCB) which could generatehyperacusis because the LOCB terminals can evoke eitherslow enhancement (cholinergic transmission) or suppression(dopaminergic) of auditory nerve response . On the otherhand, mood disorders as anxiety and chronic stress lead toincreased release of endorphins in the IHC-auditory nervesynapses. These substances increase the excitatory effect ofthe glutamate. The inhibitory neurotransmitter GABA actsat several levels on the acoustic pathways so a decrease ofGABA will increase neural activity and could be correlatedwith hyperacusis.
Hyperacusis may be associated with ear pathologies likeMenieres disease, perylimphatic fistula, sudden sensorineu-ral hearing loss, acoustic trauma, otosclerosis, Bells facialpalsy, and Ramsay Hunt syndrome (Table 2). The conductivehyperacusis is associated with dehiscence of the superiorsemicircular canal  which simulates the effect of a thirdwindow. In this condition the patient may have normalair conduction thresholds on pure audiometry with a boneconduction better than normal. The consequence is a hyper-awareness of somatosounds. In addition, CNS disorders likemigraine, depression, posttraumatic stress disorders, mul-tiple sclerosis, benign intracranial hypertension, Tay-Sachs
Table 1: Etiopathology of tinnitus.
Atherosclerotic disease (carotid and subclavian)Dural arteriovenous fistulasCarotid-cavernous fistulaAneurysm (giant)Fibromuscular dysplasia of carotid arteryCarotid artery dissectionAberrant internal carotid arteryHyperdynamic states (anemia, thyrotoxicosis, andpregnancy)HypertensionInternal auditory canal vascular loopsGlomus jugulare tumorBenign intracranial hypertensionSigmoid or jugular diverticulumHigh jugular bulbTransverse or sigmoid stenosisCondylar vein abnormalities
SomatosensoryPalatal and middle-ear myoclonusTMJ alterations (synchrony with jointmovements)
Cerebellopontine angle tumorsNeurodegenerative diseases (dementia)EpilepsyAuditory hallucinationsMigraine
Ear waxAcute otitis mediaOtitis media with effusionChronic otitis mediaCholesteatomaOtosclerosisOssicular chain traumaOssicular malformationsExternal- or middle-ear cancerLabyrinth malformationsGenetic hearing loss (syndromic andnonsyndromic)Immune mediated inner-ear diseaseCochlearot otoxicityMeniere diseasecochlear endolymphatichydropsVIII cranial nerve tumorAcoustic traumaSudden deafnessBarotraumaLabyrinthitis (bacterial, viral, tuberculosis, andfungical)Auditory neuropathyCentral auditory processing disorders
DepressionAnxietySomatoform disordersObsessive compulsive disorderPosttraumatic stress disorderPsychosis
syndrome, Williams syndrome, and Lymes disease may berelated to hyperacusis (Table 2).
Journal of Geriatrics 3
Table 2: Peripheral and central conditions associated with hypera-cusis.
Menieres diseasePerilymphatic fistulaSudden deafnessAcoustic traumaOtosclerosis
After surgical procedures PoststapedectomyTranstympanic tube placement
Stapedial reflex disorders Ramsay Hunt syndromeBells facial palsy
MigraineDepressionPosttraumatic stress disorderHead traumaLymes diseaseWilliams syndromeBZD dependenceSerotonin dysfunctionTay-Sachs syndromeMultiple sclerosisBenign in