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Paracuses and Hyperacusis

Hyperacusis, mechanisms, diagnosis and therapy (Baguley and Andersson, 2007)

Neurophysiological models

Paracuses

· Disturbance in auditory perception (other than loss of hearing sensitivity) · Musicians are more sensitive to detecting it, people infrequently complain about it (unable to recognize, confuse, mildly irritating..) · Hyperacusis is the most clinically encountered type

Paracuses

· Intensity-related phenomena · Frequency-related phenomena · Localizing dysfunction

Frequency-related phenomena

· Diplacusis: ­ Double hearing (sound will have a different tone in each ear) ­ Meniere's disease? First to disappear on treatment? ­ Cochlear otosclerosis, fenestration operations ­ Potassium iodide medication, chloroform inhalation

Diplacusis

· Damage to the fine tuning mechanism of the organ of corti (outer hair cell dysfunction?) · Lower intelligibility of speech, the benefits of hearing aids are debatable · PTA, speech discrimination, otoacoustic emissions · Diplacusimetry, psychoacoustic tuning curves

Sound localization dysfunction

· Intensity and phase difference of sounds are important for sound directionalization · Time difference, the role of the auricles · Dysstereoacusis: ­ Can be seen frequently in patients with supra tentorial lesions (central dysfunction) ­ Can be the presenting symptom in vestibular shwannoma

Intensity-related phenomena

· Paracusis Willisii: ­ Frequently mentioned with otosclerosis ­ But it is a general feature of conductive hearing loss ­ Patient's can hear better in noisy environment ­ People tend to raise their voices in noisy environment?

Hyperacusis

· Unusual tolerance to ordinary environmental sounds (Vernon, 1987) · Consistently exaggerated or inappropriate responses to sounds that are neither threatening nor uncomfortably loud to a typical person (Klein et al, 1990)

Other terms

· Loudness recruitment: ­ Abnormal growth of loudness due to cochlear hearing loss, and in particular OHCs dysfunction (mechanism?) ­ Sounds of moderate intensity perceived as uncommonly loud (ABLB, SISI score?) ­ Sounds of low intensity perceived as abnormally uncomfortable (Hyperacusis) ­ Cross over?

Other terms

· Phonophobia: ­ Emphasises the emotional impact of the sensitivity to sounds, used more in neurological literature ­ Phonophobia/photophobia accompanying migraine attacks ­ Misophonia: A term to describe disliking of sound without the phobic element (Jestreboff, 2003)

Other terms

· Noise sensitivity in psychiatric disorders: ­ Startle reflex in post traumatic stress disorders ­ The association of noise sensitivity and depression ­ Improvement of hyperacusis after treatment of depression in tinnitus patients?

Hyperacusis and tinnitus

· 9 % point prevalence (Andersson, 2002) · 40-60% in patients attending tinnitus clinic · In patients with primarily hyperacusis complaint, tinnitus estimates varies between 86% (Anari et al, 1999) and 21% (Andersson et al, 2002) · Hyperacusis as a precursor to the development of tinnitus

Severe hyperacusis

· 4-5% of population have severe tinnitus · 40% of these have significant hyperacusis · Severe hyperacusis : 2% ­ Jastreboff, 2000 ­ Baguley and Andersson, 2007

Neurophysiological models and mechanisms

Serotonin ( 5-HT)

· First recognized as a powerful vasoconstrictor and isolated by Page (1948) · 5 Hydroxytryptamine (5-HT) · Naturally produced in the pineal gland, and its precursor (amino acid Tryptophan) is rich in bananas, milk, Turkey, plums · 90% of Serotonin in the body is in the intestine

· Hyperactivity of the auditory nerve (Moore, 1995) · 5-HT (Marriage and Barnes, 1995) · Endogenous opioid peptides ( Sahley et al, 1996 ) · Auditory efferent dysfunction · Plastic change leading to increased central auditory gain

5-HT

· One role of 5-HT, is as a neurotransmitter, regulating various functions like sleep, memory and learning, temperature regulation, mood, appetite, behaviour, cardiovascular function, muscle contraction, endocrine regulation and depression. · 5-HT released at synaptic clefts in the brain regulate protein binding and change electrical state of the cell, either stimulatory or inhibitory

5-HT and depression ( The molecule of happiness)

· Low serotonin levels are believed to be the cause of many cases of mild to severe depression which can lead to symptoms such as anxiety, apathy, fear, feelings of worthlessness, insomnia and fatigue. The most concrete evidence for the connection between serotonin and depression is the decreased concentrations of serotonin metabolites in the cerebrospinal fluid and brain tissues of depressed people

Serotonin ( 5-HT )

· Serotonergic fibres and terminal endings found throughout central auditory pathway (Raphe Neucli) through the medulla, pons and midbrain · Postulated role of modulating sound perception or determination of significance ­ ( Thompson et al, 1994, Simpson and Barnes, 2000 )

Marriage and Barnes (1995)

The Journal of Laryngology and Otology October 1995, Vol. 109, pp. 915-921

Neurological conditions associated with Hyperacusis

· (f) Tay-Sach's disease or gangliosidosis type 2 · (Gordon et al, 1988; Gascon et al, 1992). · (g) Post-traumatic stress disorder. · (h) Chronic/post-viral fatigue syndrome (CFS/ PVFS) or myalgic encephalomyelitis (ME) (Behan and Bakheit, 1991; Merry, 1991).

Neurological conditions associated with hyperacusis: (a) Migraine (Solomon et al, 1992). · (b) Depression (Carmen, 1973). · (c) Pyridoxine deficiency (Oppe, 1992). · (d) Benzodiazepine dependence (Lader, 1984). · (e) Musicogenic epilepsy (case study by Fujinawa et al, 1977).

Hypothesis

· Many conditions associated with hyperacusis, especially Migraine and tinnitus (probably accounts for 90% of cases of hyperacusis), are strongly related to dysfunction in 5-HT metabolism, probably reduction of 5-HT activity in the forebrain

Problems with 5-HT hypothesis

· Non-specific ( Phillips and Carr, 1998 ) · Possible role of SSRI medication: ­ A Cochrane review has found no evidence of the its effects on tinnitus treatment ­ Interest in the states, under investigation

Plasticity in central auditory system

The role of sensory deprivation · Tonotopic organization through the auditory system means that certain frequency areas on the basilar membrane supplies certain regions in the central auditory system with afferent signals · Damage to the cochlea, resulting in SNHL will lead to loss of afferent information leaving this specific area (frequency region)

· Plasticity first proposed by Ramon y Cajal ( 1852 - 1934 ) The ability of the brain to re-organize itself · Caused by

­ Reorganization following an insult (sensory deprivation as an example) ­ Adaptation and change of functions

Sensory deprivation theory

· Corresponding areas in the central auditory system become starved (deprived) of sensory stimulation · This might lead to: ­ Increased level of spontaneous activity ­ Plastic rearrangement of neurones leading to abnormal firing patterns · This can be perceived as tinnitus and hyperacusis

Recent PET scan findings Seng-Ha Oh (2010)

· Pre and post cochlear implantation in pre lingual and post lingual hearing loss · PET looks at auditory cortical metabolism · Wider pre-operative hypometabolism of the auditory cortex is an indication of BETTER speech abilities post implantation · The more the duration of deafness the LESS the extent of hypometabolism in the auditory cortex

Final thoughts

· Hyperacusis is a specific term and should not be confused with other phenomena · The theories of causation are still not proven, though strong associations with cochlear damage, tinnitus and migraine should provide a connection to the pathophysiological mechanisms of these conditions

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