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Deafness

Deafness is a general term that describes the complete loss of the ability to hear. Deafness may be congenital or acquired, and may be provoked by anomalies affecting any part of the auditory system, e.g., outer, middle or inner ear as well as the vestibulocochlear nerve and higher brain centers.


Presentation

While older children and adults generally report their inability to hear, deafness may not be easily recognized in neonates and infants. Here, a progressive decline of vocalization and a considerable delay of language and speech acquisition may not be noted by parents before their children are aged six months and older. In such cases of pre-lingual deafness, communication skills cannot be developed appropriately unless the child's condition is recognized and treated at an earlier point in time. In order to assure the correct diagnosis of congenital deafness, newborn hearing screens have been implemented in many countries. However, such programs are often lacking in developing countries [8]. Owing to the inability to hear and thus the inability to interact with their surroundings, many deaf children are initially diagnosed with behavioral disorders like autism or attention deficit. Parents may describe their child to be stubborn, not willing to listen to their advice. Consequently, hearing evaluations may be indicated in case of a suspected behavioral disorder.

Depending on the underlying disease, deaf patients may present a wide variety of additional symptoms that may or may not predominate the clinical picture. Individuals suffering from Down syndrome, for instance, are generally diagnosed with this genetic disorder before their inability to hear becomes apparent [9]. This also applies to other syndrome-related forms of deafness and developmental defects. In contrast, a progressive, bilateral hearing loss is the main and often the only symptom of presbycusis.

Short Stature
  • Here, we report 2 brothers with peculiar gestalt, short stature, and hearing loss, who harbor an X/Y translocation.[ncbi.nlm.nih.gov]
Diplopia
  • The patient's VA improved from 20/200 both eyes (OU) to 20/40 OU with successful fitting of GP lenses, which additionally relieved the patient's otherwise intractable monocular diplopia.[ncbi.nlm.nih.gov]
Hyperkeratosis
  • A 30-year-old man presented with generalized erythro-hyperkeratosis and deafness and complaints of decreased visual acuity, tearing, and photophobia.[ncbi.nlm.nih.gov]
Short Arm
  • R-banding identified a derivative X chromosome with an abnormally expanded short arm. The mother was detected as a carrier of the same aberrant X chromosome. aCGH disclosed a 3.1-Mb distal deletion of chromosome region Xp22.33pter.[ncbi.nlm.nih.gov]
Hearing Problem
  • Untreated, hearing problems can get worse. If you have trouble hearing, you can get help. Possible treatments include hearing aids , cochlear implants , special training, certain medicines, and surgery.[medlineplus.gov]
  • But Johnson's hearing problems are just the latest of the band's woes.[news.yahoo.com]
  • Social activities may be more challenging than it is for children with no hearing problems.[medicalnewstoday.com]
Hypertelorism
  • The probands had short stature, hypertelorism, midface hypoplasia, sensorineural hearing loss, normal intelligence as well as slight radial and ulnar bowing with brachytelephalangy.[ncbi.nlm.nih.gov]
Posture Abnormal
  • Moreover, mild enlargement of semicircular canals, postural abnormalities and different types of hearing thresholds were found in female carrier of this POU3F4-variant.[ncbi.nlm.nih.gov]

Workup

Distinct diagnostic measures are available to assess development and function of anatomical structures forming part of the auditory system. The above explained physiological conduction and processing of acoustic waves may serve as a reference for a possible upstream workup. Of course, anamnestic data and clinical presentation of the individual patient may allow for the direct selection of a specific diagnostic approach.

  • Auricles, external auditory canal and tympanic membrane are readily observable with an otoscope. Pneumatic otoscopy is generally used in otitis media diagnostics.
  • The otolaryngologist disposes of further techniques that may be helpful in diagnosing deafness, e.g., tympanometry and electrocochleography.
  • Functional tests are generally indicated to evaluate the degree of hearing loss and to diagnose the condition of deafness: In case of neonates, auditory brainstem response may be conducted [10]. This test does not depend on the patient to actively react to stimuli, since it serves to ascertain the brain's response to sound. Otoacoustic emissions originate from the inner ear; the respective test does not depend on the patient actively partaking in the examination. This does not apply to behavioral audiometry, and thus, this technique is little specific and sensitive in newborns.
  • If the patient is able to cooperate, tests of balance may yield important findings regarding the condition of the middle ear and processing pathways.
  • Magnetic resonance imaging and computed tomography allow for an evaluation of structures not accessible from the outside.
  • Specific tests, e.g., serological or genetic screens, are indicated if determined infectious diseases or genetic disorders are suspected.
Trichophyton Rubrum
  • We identified a mutation (p.G12R) in the GJB2 gene in this patient with Trichophyton rubrum infection. Immunohistochemistry staining revealed a lower expression of TLR2 and no significant difference in TLR4.[ncbi.nlm.nih.gov]

Treatment

In general, treatment should be initiated as early as possible to avoid irreversible damage to the cochlea or neural structures. In case of neonates and infants, early therapy of deafness is a prerequisite for an undisturbed development of communication skills. Causal therapy of deafness may comprise administration of antimicrobial and anti-inflammatory drugs, myringotomy, tumor resection, reconstructive surgery and a wide variety of other measures depending on the underlying disease. In contrast, hearing aids and/or cochlea implants are required if tissue damage is not reversible by means of the aforementioned measures. Patients suffering from bilateral sensorineural deafness may benefit from brainstem implants. Even if the ability to hear cannot be regained completely, day-to-day communication is largely facilitated if patients hear how words are intonated. It is also very helpful if they can hear environmental sounds like honking cars.

Deaf patients should be offered the possibility to attend linguistic courses guided by speech therapists, and possibly to learn lipreading. Their families should be trained regarding an appropriate dealing with affected individuals. Ideally, such educational programs would be available to any interested person.

Prognosis

Prognosis largely depends on the underlying disease. There is no causative treatment for genetic disorders and congenital malformations, but hearing aids and cochlea implants may significantly improve the quality of life of an affected individual. With regards to infectious diseases like otitis media, morbidity has decreased considerably during the last decades, particularly because more effective drugs have become widely available. In contrast, neural damage is still largely irreversible. Thus, the outcome in cases of sensorineural hearing loss is often worse than that of conductive deafness.

Moreover, pre-lingual deafness may severely interfere with the acquisition of language and speech. Here, early diagnosis and treatment are of utmost importance to improve the infant's ability to hear in order for them to develop appropriate communication skills [7]. With respect to the latter, further unfavorable prognostic factors are inner ear anomalies, a narrow bony cochlear nerve canal as well as additional perinatal issues [2].

Etiology

As has been indicated above, functional impairment of a wide variety of anatomical structures may provoke deafness. From an etiological point of view, the inability to hear most commonly results from genetic disorders, pre- or postnatal infections, neoplasms or trauma.

  • Deafness may be inherited with an autosomal recessive (75%), autosomal dominant (20%) or X-linked trait (<5%) [3]. In this context, it may be diagnosed in patients suffering from Alport syndrome, Mondini dysplasia, and Usher syndrome. Also, sequence alterations of mitochondrial DNA may interfere with the ability to hear, as is the case in MELAS syndrome and Kearns-Sayre syndrome. Moreover, complex genetic disorders like Down syndrome may be associated with deafness. Of note, hereditary deafness is not necessarily present at birth: Progressive hearing loss, delayed symptom onset and fluctuating hearing impairment may also be observed.
  • Intrauterine infections with pathogens like Treponema pallidum (congenital syphilis), rubella virus (congenital rubella syndrome) [4], or Toxoplasma gondii (toxoplasmosis) may interfere with the embryonal or fetal development of the auditory system. Similar effects may be mediated by teratogenic drugs.
  • With regards to neoplasms, hearing loss is a common complication of vestibular schwannoma. This tumor originates from Schwann cells coating the vestibulocochlear nerve. In fact, this benign neoplasms is often referred to as acoustic neuroma. It is often detected in patients suffering from neurofibromatosis type 2.
  • Traumatic lesions involving the temporal bone often comprise both conductive and sensorineural portions of the auditory system. Although it has been proposed that constant exposure to loud noises may cause hearing loss by traumatic cochlea damage, the precise pathomechanisms are not yet fully understood.

Due to its clinical importance, sudden hearing loss shall be mentioned as another entity that may lead to deafness. It is generally considered idiopathic and can therefore not be assigned to any of the aforementioned groups.

This list is by far not complete and the interested reader is referred to excellent reviews available elsewhere [1].

Epidemiology

Deafness may affect people of both genders, any race and any age. However, there are significant differences regarding the etiology and incidence of deafness in distinct patient groups.

  • In general, no gender predilection is known. However, hereditary deafness inherited with an X-linked trait may affect females and males differently. X-linked deafness, for instance, is more severe in men [5].
  • With regards to pediatric patients, severe hearing impairment or deafness affects about 1 in 1,000 neonates and usually results from genetic disorders or intrauterine infections and consequent malformations of the auditory system [6]. About 2 in 1,000 pediatric patients acquire severe hearing impairment during infancy or childhood. Here, otitis media often causes conductive deafness. Incidence rates of middle ear infections are lower in adolescents, but patients in their second decade of life are particularly prone to traumatic hearing loss. Adults may present with hearing loss due to otosclerosis, and the elderly are often diagnosed with presbycusis.
Sex distribution
Age distribution

Pathophysiology

There is no unique chain of pathophysiological events leading to deafness. In order to understand which anatomic structures may be implicated in hearing loss, it is important to comprehend how acoustic waves are recognized.

Acoustic waves propagate in form of otherwise unperceivable alterations in air pressure. These are captured by the auricles, which function as funnels and guide those waves into the external auditory canal. Eventually, they reach the tympanic membrane and cause it to vibrate. These vibrations are transmitted to the auditory ossicles malleus, incus, and stapes. They are suspended in the tympanic cavity and connect to the so-called oval window, which is the point of entry to the inner ear. If the ear is exposed to loud noises, a reflectory contraction of the stapedius muscle attenuates the transmission of vibrations from the stapes to the oval window and thereby protects the inner ear. The inner part of the ear contains the bony labyrinth and within that structure, the membranous labyrinth can be found. It is filled with endolymph and perilymph and does not only perceive acoustic stimuli - which occurs in the cochlea -, but does also play a pivotal role in maintaining balance. The latter is achieved by the vestibular system.

Any disturbance affecting the conduction of acoustic waves into the cochlea may cause conductive hearing loss. Accumulation of fluid in the middle ear and otosclerosis are common causes of this form of hearing impairment.

Pressure waves propagating inside the cochlea stimulate the organ of Corti, the sensory epithelium lining its ducts. Here, hair cells register pressure fluctuations. Depending on the frequency of the acoustic wave, sensory cells located in different parts of the cochlea are stimulated. They are all connected to the auditory nerve, i.e., the cochlear nerve, which is, in turn, part of the eighth cranial nerve, the vestibulocochlear nerve. Activation of ion channels and release of excitatory neurotransmitters allows for the conversion of mechanical stimuli into electrical impulses that may be conducted to higher centers in the brain. After passing medulla, pons and brainstem, the auditory cortex is reached.

If an effective conduction of electrical impulses to the brain or processing of those signals is not possible, the affected individual suffers from sensorineural hearing loss. This condition may be provoked by cerebral ischemia, hemorrhages or inflammatory processes as well as presbycusis. Ototoxic drugs may also destroy cochlear hair cells and cause this type of deafness.

Prevention

For many forms of deafness, no specific preventive measures can be recommended. However, the risk of developmental defects may be reduced by complying with vaccination plans, by maintaining a healthy lifestyle during pregnancy, by avoiding possible sources of infection. The latter also applies to postnatal care of the ear. Exposure to loud noises should be avoided as far as possible throughout life and, if this is not possible, ear protectors should be worn.

Summary

Deafness, sometimes also referred to as hearing loss, is a very broad term that describes a symptom rather than a particular entity. Hearing is a complex cognitive process that depends on the correct functioning of all organs comprising the auditory system. In brief, any severe disturbance of acoustic wave perception, mechanic conduction, conversion into electrical impulses, conduction of nerve signals and processing in the central nervous system may cause hearing impairment and eventually deafness. Accordingly, the following forms of deafness may be distinguished:

  • Conductive deafness. Lesions affect afferent structures preceding acoustic wave conversion in the cochlea.
  • Sensorineural deafness. Despite correct transmission of pressure waves into the cochlea, electrical impulses cannot be generated, cannot be conducted via the vestibulocochlear nerve or processed in the auditory cortex. With regards to the latter, auditory processing disorders are sometimes considered a distinct class of hearing impairment [1].
  • Psychogenic deafness. Affected patients do not show any organic cause of hearing loss, they actually hear but are unable to associate perceived sounds with their surroundings.

Deafness may affect both ears or occur unilaterally, whereby unilateral deafness may or may not be associated with contralateral hearing impairment. Complete bilateral hearing loss severely compromises life quality and this applies particularly to pre-lingual forms of deafness [2]. Here, language and speech acquisition is impaired by the inability to hear. In contrast, acquired hearing loss does typically not affect the patient's ability to speak.

Moreover, deafness is not necessarily an irreversible condition. If the underlying disease can be treated before permanent damage to involved anatomic structures occurs, the ability to hear may be regained partially or completely.

Patient Information

Deafness describes the complete loss of the ability to hear. This condition is severely disabling and thus compromises life quality. In infants, hearing impairment additionally interferes with language and speech acquisition. Fortunately, some forms of deafness can be treated or, even better, avoided. For instance, congenital deafness may result from prenatal infections with pathogens like Treponema pallidum (syphilis), rubella virus (congenital rubella syndrome), or Toxoplasma gondii (toxoplasmosis). This also applies to consumption of alcohol and drugs. With regards to acquired deafness, constant exposure to loud noises, trauma and neoplasms may cause damage to anatomical structures forming part of the auditory system. The former can be reduced by taking preventive measures.

Therapy needs to be adjusted to the cause of deafness. If causal treatment is not available, hearing aids, cochlea implants or brainstem implants may improve the patient's ability to distinguish words and environmental sounds. Speech therapy and educational programs may be attended by the patient and their family in order to learn how to deal with each other.

References

Article

  1. Paludetti G, Conti G, W DIN, et al. Infant hearing loss: from diagnosis to therapy Official Report of XXI Conference of Italian Society of Pediatric Otorhinolaryngology. Acta Otorhinolaryngol Ital. 2012; 32(6):347-370.
  2. Kang DH, Lee MJ, Lee KY, Lee SH, Jang JH. Prediction of Cochlear Implant Outcomes in Patients With Prelingual Deafness. Clin Exp Otorhinolaryngol. 2016.
  3. Bademci G, Lasisi A, Yariz KO, et al. Novel domain-specific POU3F4 mutations are associated with X-linked deafness: examples from different populations. BMC Med Genet. 2015; 16:9.
  4. Dewan P, Gupta P. Burden of Congenital Rubella Syndrome (CRS) in India: a systematic review. Indian Pediatr. 2012; 49(5):377-399.
  5. Marlin S, Moizard MP, David A, et al. Phenotype and genotype in females with POU3F4 mutations. Clin Genet. 2009; 76(6):558-563.
  6. Morton CC, Nance WE. Newborn hearing screening--a silent revolution. N Engl J Med. 2006; 354(20):2151-2164.
  7. Nicholas JG, Geers AE. Effects of early auditory experience on the spoken language of deaf children at 3 years of age. Ear Hear. 2006; 27(3):286-298.
  8. Walsh M, Redshaw E, Crossley E, Phillips C. Identifying the Optimal Age to Perform Newborn Screening for Hearing Loss in Uganda. Ann Med Health Sci Res. 2015; 5(6):403-408.
  9. Ramia M, Musharrafieh U, Khaddage W, Sabri A. Revisiting Down syndrome from the ENT perspective: review of literature and recommendations. Eur Arch Otorhinolaryngol. 2014; 271(5):863-869.
  10. Rouillon I, Parodi M, Denoyelle F, Loundon N. How to perform ABR in young children. Eur Ann Otorhinolaryngol Head Neck Dis. 2016.

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