Pediatric hearing loss is a broad category that covers a wide range of pathologies. Early detection and prompt management are essential for the development of normal language and psychosocial functioning, as well as to identify potentially reversible causes or other underlying problems. Hearing is measured in decibels, and the severity of hearing loss is graded by hearing thresholds. Normal hearing range is 0-20 decibels (dB) which equates to being able to perceive sound quieter than a whisper. Mild hearing loss corresponds to a range of 20-39 dB, moderate 40-69 dB, severe 70-89 dB and profound is greater than 90 dB.
There are three main types of hearing loss; conductive, sensorineural and mixed. The former typically occurs due to a problem transmitting sounds at the level of the external or middle ear. The major cause of conductive hearing loss in children is otitis media with effusion (glue ear). Sensorineural hearing loss results from a disruption of the auditory pathway at any point from the cochlea of the inner ear through to the brainstem, and despite being relatively uncommon in children as a whole, it is the primary cause of permanent hearing loss in the pediatric population. Mixed hearing loss occurs when there are both conductive and sensorineural components.
Hearing loss can be broadly characterized as congenital or acquired in the pediatric population.
Congenital hearing loss can be classified as genetic and non-genetic in etiology. The former category is responsible for greater than half of congenital causes and can be due to either an autosomal dominant, recessive or sex-linked mutation. Genetic causes are often further subdivided into syndromic versus non-syndromic categories based on whether the patient suffers from an underlying genetic syndrome. Approximately 30% of the genetic causes of hearing loss are syndromic. The most common cause of congenital hearing loss is autosomal recessive non-syndromic hearing loss.
TORCH organisms (toxoplasmosis, rubella, cytomegalovirus (CMV) and herpes) have been identified as key infective causative agents. CMV is the most common cause of congenital non-genetic hearing loss in the developed world. Other congenital causes include trauma, ototoxic medications used in the antenatal period and several perinatal risk factors such as prematurity, low birth weight, and hyperbilirubinemia.
Acquired Hearing Loss
Otitis media with effusion is the number one cause of acquired hearing loss in children. It is beyond the scope of this article to cover this in detail, but it classically has a bimodal beak at 2 years and 5 years of age and is characterized by a conductive hearing loss associated with flattened tympanogram. It typically resolves without intervention as the eustachian tube matures or following the insertion of a ventilation tube in the middle ear. Adenoidal hypertrophy can contribute to this clinical picture.Infections also present another major category for acquired hearing loss, with a particularly strong link with bacterial meningitis, mumps, and measles. Other reasons include primary otological pathologies such as cholesteatoma, impacted wax and otosclerosis as well as trauma.
Hearing loss occurs in 1-3 newborns per 1000 births, with 1-2 per 1,000 suffering from permanent childhood hearing impairment. There is a slightly increased prevalence of hearing loss in boys compared to girls with a ratio of 1.16:1.0. There are around 45,000 children with hearing loss in the UK, half of which are congenital in origin.
Hearing loss can present in different ways depending on the age of the child. Hearing loss in neonates is almost exclusively picked up via newborn screening programme assessments. In older children, parents or other professionals such as school teachers, may notice delayed language skills, behavioral problems or listening to the television at raised volumes. In the history, it is important to ascertain whether there are any associated otological symptoms such as otorrhoea, otalgia, tinnitus, or vertigo. A thorough history is required including asking about any other neurological symptoms, medical history including drug history and precipitating events such as trauma, recent viral infections or new medications.
The examination will involve assessing the ear including the appearance of the pinna particularly inspecting for any deformities such as microtia or anotia. Otoscopic examination of the external auditory canal and tympanic membrane is crucial, with special attention on the attic for cholesteatoma. An examination should also include assessment of cranial nerves, a full neurological assessment, and assessment of balance depending on the age of the child.
Hearing assessment in children is age and ability dependent and will be addressed per age group here.
In the UK, all newborns and those who require less than 48 hours of special care in neonatal intensive care (NICU), are offered evoked otoacoustic emission (OAE) testing within the first 4-5 weeks of birth as part of a Newborn Hearing Screening Programme. Oto-acoustic emissions are outer hair vibrations that are detected in the external auditory canal in response to a click stimulus. This test is easy to perform and does not involve a general anesthetic.
Automated Auditory Brainstem Response
This investigation is offered to all newborns who have spent over 48 hours in the neonatal intensive NICU and is also offered to those who do not pass two OAE tests. It involves measuring brainstem electrophysiological responses to click stimuli using electrodes placed on the scalp. This assesses hearing throughout the entire hearing pathway; form the external ear through to the brainstem.
An assistant engages the child’s attention, and the tester, whilst placed behind and to the side of the child, makes sounds of different intensities. The child is assessed to see whether they turn to the side of the noise.
9 – 36 months
Visual Reinforcement Audiometry
The child is placed at a table with some toys with two speakers either side that produce sounds. If the child looks towards the speaker playing a sound they are delivered a visual reinforcement (such as a flashing light).
Conditioned Play Audiometry
The child is conditioned to perform a task in response to an auditory stimulus such as placing a ball in a cup. Once the task is learned the sound volume is reduced in order to determine their hearing threshold.
Over 60 months
Pure Tone Audiometry
A 5 years of age most children can undergo pure tone audiometry. Hearing thresholds are determined by presenting sounds of various frequencies and at various intensities until the quietest sound is reliably detected 50% of the time. This test requires a higher level of attention and therefore is rarely done below the age of 5 years.
Additional investigations will be tailored to the precise clinical picture. In syndromic children, chromosomal testing is advised. There is also a role for imaging in the form of either computed tomography (CT) or magnetic resonance imaging (MRI)
Treatment for hearing loss depends on the type of hearing loss present, the underlying cause and often there is an element of patient/parent preference.
A key element to managing hearing loss in family support and advice. There are a number of behavioral measures that can be used to improve hearing without the need for adjuncts or surgical intervention. The principles of this are rooted in creating a deaf-friendly environment such as limiting background noise, talking face-on, and clear intonation. There are also a range of hearing assist devices that can be used such as television listeners. It is also crucial that the child educational support which could be in the form of special equipment or positioning in the classroom.
There are a variety of hearing aid types that are used in specific situations. Each type will be briefly covered here.
Binaural air conduction hearing aids rely on at least a partially functioning inner ear and central auditory processing system. They work by converting sound detected by a microphone into digital signals which can then be amplified and re-converted into audible sounds that are transmitted to the ear. They can be classified based on whether these key parts are housed in an earpiece that sits externally (behind-the-ear), inside the canal (in-the-canal) or further inside the canal (in-the-ear).
Bone conduction hearing aids are used typically in a conductive hearing loss when there are ear problems that impede the use of a regular air conduction hearing aid such in children with external ear deformities (anotia, microtia) or when there are chronic ear infections. Bone-anchored hearing aids (BAHA) are fitted surgically under general anesthetic over two stages. A titanium implant is fixed into the temporal bone. Through this setup, a sound is conducted directly to the inner ear by way of the bone, bypassing the middle ear. Typically the BAHA is fitting from 4 years of age once the temporal bone has developed, however, soft-band bone conducting aids can be used from several weeks of age.
Contralateral routing of sound (CROS) hearing aids are used when there is a unilateral sensorineural hearing loss. The sound in the problem ear is diverted to the better hearing ear without amplification. In cases where neither ear has normal hearing but one side is significantly better, a variation on this can be used called a BiCROS.
Cochlear implants work by converting sound into digital signals that are transmitted directly to the auditory nerve via an electrode array. In the UK, the National Institue of Clinical Excellence (NICE) recommends cochlear implants in children who have severe to profound deafness in one or two ears with minimal benefit from conventional hearing aids after 3 months of use.
Ventilation tubes are indicated in conductive hearing loss secondary to flue ear, or less frequently in the context of recurrent otitis media. They are inserted surgically and typically self-extrude on average a year of insertion. Children found to have cholesteatoma invariably require surgical clearance of disease via a mastoidectomy.
Prognosis of hearing loss will vary considerably based on the underlying aetiology. Congenital sensorineural hearing loss left untreated will invariably not improve or can progress, such as in the case of congenital CMV. On the other side of the spectrum, glue ear shows an excellent prognosis with resolution of symptoms even without intervention.
Hearing loss in the pediatric population must be managed as part of a multi-disciplinary team. This will involve a range of medical doctors including otolaryngologists, audiologists, speech therapists, geneticists, and pediatricians. In addition to this, audiologists, speech and language therapists, educational psychologists and specialist nurses are vital parts of the wider team. Delivery of the highest quality of care and support requires a coordinated approach amongst services including between primary and secondary care. It is important to identify hearing loss at an early age, because the earlier treatment is offered, the better the prognosis. (Level V)
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