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Hyperacusis: Review and Clinical Guidelines

Dimitar Marev

Department of Otolaryngology, University of Medicine, Varna, Bulgaria

ABSTRACT

Objective: The goal of the folloing article is to reviw the current known causes of hyperacusis and the different hypotheses concerning its etiology, and to suggest clinical guidelines.
Data sources: The literature used has been published in English for the last thirty years.
Study selection: A review of the literature with the aid of the MEDLINE database, using the following key words: hyperacusis, intolerance to sound, loudness discomfort level, and phonophobia.
Data extraction: The data collection includs clinical studies, case reports and laboratory studies.
Conclusion: Hyperacusis was shown to be caused by pathologic conditions of the peripherial auditory system, diseases of the central nervous system, and hormonal and infectious diseases. In some cases there was no known cause. The pathophysiology of hyperacusis probably involves a central mechanism rather than a peripheral one. Suggested clinical guidelines and treatment are discussed.
Key Words: Hyperacusis, Sound intolerance, Loudness discomfort level, Phonophobia.
Pro Otology 2-3: 119-121, 2003

INTRODUCTION

The term hyperacusis denotes increased sensitivity to sound in levels that would not trouble a normal individual. This auditory sensitivity is characterized by a painful or troublesome sensation when the patient is exposed to sound. The terms phonophobia, noise sensitivity, audiosensitivity, hyperacusis dolorosa, and reduced tolerance to noise have been used in the same context. The types and intensities of noises causing discomfort to people with hyperacusis may vary between patients. Characteristically, the discomfort is elicted by noise from mashinery, but sometimes even quiet sounds, such as those coming from a distance or the sound of paper being folded, can couse discomfort. Tiredness and anxiety are reported to aggravate hyperacusis (1).

ETIOLOGY

The causes of hyperacusis can be divided into four main groups: clinical conditions involving the peripheral auditory system, clinical conditions involving the nervous system, hormonal and infectious diseases, and unknown causes.

Clinical conditions involving the peripheral
auditory system Bell’s palsy

Hyperacusis has been reported in 29% of patients with Bell’s palsy. Lowered loudness discomfort levels (LDLs) to speech, and rollover in alternate binaural loudness balance (ABLB) at higher intensities, were demonstrated among patients. The absense of the stapedial function is the common characteristic in stapedectomized patients, and this suggests a common pathology (2). In on report, data analysis showed no relationship between stapedial muscle paralysis and hyperacusis in Bell’s palsy patients, suggesting a different mechanism. In another report, acoustic reflex thresholds (ARTs) of a patient with transient facial paralysis and hyperacusis were measured. Reduced amplitude of the ipsilateral ART in the affected side was interpreted as involvement of seventh nerve fibers proximal to the stapedial innervation. Large ipsilateral and contralateral impedance changes at the beginning of stimulation of the affected ear were noticed. This finding was interpreted as eighth nerve involvement on the affected side, causing less downregulation of the stimulus. This downregulation effect is alleged to be mediated by the acoustic tensor reflex and could explain the mechanism of hyperacusis in Bell’s palsy.

Recruitment

Sensorineural hearing loss is accompanied by recruitment, which is abnormal loudness growth. This phenomenon could be demonstrated with the aid of auditory brainstem response, ABLB, and LDL. Recruitment is characterized by narrowing of the dynamic range caused by the higher detection threshold. Usually the discomfort level is unaffected. Unlike hyperacusis, recruitment is associated with damage to the cochlear outer hair cells and should therefore be considered as a separate phenomenon (3).

Noise-induced hearing loss

In one report, reduced discomfort levels were detected in command board operators, who were exposed to noise for 11 years or more and consequently experienced noise-induced hearing loss. The discomfort level decreased from 120 dB to 70 dB the longer the worker was exposed to noise. Substantial reduction in the dynamic range, which was narrowest at 4000 Hz, was reached when hearing loss exceeded 20 dB HL. In some cases, the concomitant sensorineural hearing loss narrowedthe dynamic range to 10 dB. These findings were attributed to recruitment with malfunction of central regulation,which reduced the discomfort level (4). By contrast, Niemeyer found that the LDL rises in people exposed to industrial noises. Hyperacusis has also been experienced by musicians who are exposed regularly to loud sounds.

Diseases and syndroms involving
the central nervous system

Headache

The prevalence of phonophobia in migraineurs is reported to be between 70% and 83% during attacks and 76% attacks. Reports using LDL measurements revealed that headache-free migraineurs and people with cervicogenic headache were significantly more sensitive to sound (9). Patients with cluster headache between bouts did not differ from the control group in their sensitivity to noise.The difference in the LDL between the migraineurs and the control subjects was 12.1 dB (10). Migraineurs tested during a bout had lower LDLs than those tested between bouts.Migraineurs with unilateral or pulsating headache were more sensitive to noise than migraineurs with bilateral or pressing headache). It has been suggested that sound tolerance may form part of the diagnostic criteria for migraine.The concomitant sensitivity to light and possibly other sensory stimuli between attacks suggests a central processing mechanism (11). The increased sensitivity to quiet sounds and the dissimilarity to recruitment supports the latter hypothesis. Phonophobia was not found to be significantly greater on the symptomatic than on the nonsymptomatic side. This could be explained by the many crossover connections from side to side in the hearing pathways from the cochlear nucleus to the acoustic cortex. Speculations about the mechanism of phonophobia in migraine mentioned heightened activity of the noradrenergic locus ceruleus,or derangement in the serotoninergic midbrain raphe nuclei,which are believed to playa role in sensory processing and the pathogenesis of migraine.

Other conditions

Brain lesions causing mass effects are reported to cause hyperacusis as well. One case report described a 30-year-old woman with multiple sclerosis, who experienced intolerance to loud sounds and sound distortion after the development of a lesion on the left olivocochlear bundle in the pons. The LDL was lowered, especially on the side of the lesion. The ARTs were lowered by 5 to 10 dB in both sides. Efferent fibers from this bundle reach the cochleas bilaterally and produce an inhibitory effect. The mass effect caused by this lesion allegedly diminished the inhibitory effect on the cochlea, producing hyperacusis.

Another report described a 49-year-old man who experienced hyperacusis and palinacusis following a transient ischemic attack (13). Magnetic resonance imaging of the brain detected a lesion in the right posteroinferior thalamus,including the medial geniculate body, which was interpreted as a hemorrhagic infarction. The medial geniculate body is an integration center for the central auditory pathways. Pontine auditory hallucinosis is usually associated with impaired hearing in one or both sides, and neurologic signs related to brainstem lesions (14). Temporal lobe lesions, which leave hearing intact, may also cause auditory illusions.

Most patients with hyperacusis will probably have no other clinical condition associated with that symptom. Malingering should sometimes be suspected, especially when secondary gain is involved.

SUGGESTED CLINICAL GUIDELINES

Hyperacusis can be a symptom of a neurologic or hormonal disease affecting the auditory pathway, although it has never been discribed as the only or presenting sign (15). The following clinical guidelines are suggested for the assessment of patients with hyperacusis.

Health history

The interview should begin with a detailed description of the symptom. The physician should try to ascertain what kind of noises and what length of exposure brings about the discomfort. The physician should ask whether the discomfort is bilateral and whether the loudness discomfort appears regularly when the stimulus occurs.

The patient should be asked whether he or she has any otologic diseases, has undergone any otologic surgical procedures, feels any loss of hearing, has been exposed to acoustic trauma or to harmful noises over the long term, and has tinnitus or vestibular problems or any facial symptoms (16).

Physical examination

A thorough physical examination should be made. The physician should check for facial paralysis, skin and oral mucosal discoloration, hair distribution, fasciculations, and auricular lesions. Body temperature, pulse, blood pressure, and weight should be measured. A thorough otologic examination should be made. Neurologic examination should include the cranial nerves, the motor system, the sensory system, reflexes, and fundoscopic examination.

Audiologic tests

Pure-tone test and speech reception threshold should be measured, as well as LDL. Ipsilateral and contralateral ART may produce interesting results. Hyperacusis has been associated with abnormal acoustic reflex experience audiosensitivity (13). In one study, ART was lowered 8 dB in people with hyperacusis, but there was no statistical significance. ART was lower especially in patients with hyperacusis and hypoadrenalism or hyperthyroidism. If hyperacusis has a peripheral origin, it is likely to produce a difference between ears (17).

Loudness judgement was found to be exaggerated in patients with hyperacusis compared with normal subjects (18). Thus, ABLB and loudness growth may be useful for subjective quantification of the symptom.

An interesting attempt to define the LDL objectively was made by using the ABR. The ABR should be determined in screening for pathologicconditions in the auditory tract. Auditory-averaged electroencephalic responses showed no correlation with LDL. The addition of otoacoustic emission should be considered for defining cochlear status.

Consultation

Neurologic, endocrinologic, and psychiatric consultation should be considered if any relevant disease is suspected.

Treatment

Treatment of the underlying disease may ameliorate the symptom (16). If the clinical evaluation produces negative results, reassuring the patient that he or she does not have a clinical condition that will be harmful to health or hearing should be the first step in treatment.

Acoustic reduction of noise at work or at home may diminish the discomfort caused to the patient. Earplugs or hearing protective devices dispensed by an audiologist can aid in reducing the discomfort sensation (5). Longterm exposure of patients to low levels of stimulation that increase with time has been reported to cause desensitization of patients with hyperacusis (1).

Auditory integration training (AIT), also called auditory enhancement training or audiopsychophonology, encompasses a variety of techniques used to treat patients with communication ,behavioral, learning,and emotional disorders. These controversial techniques involve exposing the patients to noise in the form of speech and music in consecutive sessions. A reduction of the hyperacusis by AIT has been reported but has notyet been backed by data.

The association with tinnitus has led to the treatment of hyperacusis by the gradual introduction of white noise (15) with the aid of tinnitus maskers. This involves the exposure of the patient to white noise,gradually increasing in intensity. The use of desensitization with the aid of wearable tinnitus maskers was used in three patients with hyperacusis. They were exposed to a wide-band noise and were instructed to elevate the loudness of the masking sound at the end of every two weeks. The patients were treated for three months to two years. All three patients reported improvement of their hyperacusis. The effect of this treatment remains unclear. This report emphasizes the ned for objective measurements of the LDL. In one unusual case of loudness intolerance and harmonic distortion in a severely deafened ear, cochlear labyrinthectomy was used successfully to relieve the symptoms.

Conclusion

Hyperacusis is a rare symptom that can appear with many different diseases. A comprehensive clinical investigation is needed to exclude any underlying disease. The apthogenesis of hyperacusis is not yet clear, although it probably involves a central mechanism. Objective means for the identification and the evaluation of treatment of hyperacusis are warranted for the diagnosis and the evaluation of treatment. Validation of the effectiveness of the treatment of hyperacusis is yet to be done.

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