Congenital Hearing Loss

Hearing loss present at birth or arising in the first months of life, with an incidence of 1 to 3 per 1000 live births and 2 to 4 per 100 in neonatal intensive care graduates. Its clinical urgency comes from the critical period for auditory cortical development: intervention before 6 months of age produces speech and language outcomes close to normal, and every month of delay thereafter costs measurable ability.

Aetiology

Genetic causes account for 50 to 60 percent:

• Non syndromic in around 70 percent of genetic cases. Autosomal recessive in 80 percent of these, autosomal dominant in 15 to 20 percent, and X linked or mitochondrial in the remainder. GJB2 mutations affecting connexin 26 are the single commonest cause, producing prelingual, non progressive, moderate to profound loss with normal vestibular function and normal imaging.
• Syndromic in around 30 percent: Pendred syndrome with an enlarged vestibular aqueduct and goitre; Usher syndrome with retinitis pigmentosa and, in type 1, absent vestibular function and delayed walking; Waardenburg syndrome with dystopia canthorum, heterochromia and a white forelock; branchio oto renal syndrome with branchial fistulae, preauricular pits and renal anomalies; Alport syndrome with haematuria and renal failure; Jervell and Lange Nielsen syndrome with a prolonged QT interval and syncope, which is lethal if missed; Treacher Collins, CHARGE and Stickler syndromes.

Non genetic causes account for 40 to 50 percent:

• Congenital cytomegalovirus, the leading non genetic cause, responsible for roughly 10 to 20 percent of congenital hearing loss. Ninety percent of infected infants are asymptomatic at birth, and hearing loss may be delayed in onset, progressive and unilateral, which is why it escapes newborn screening.
• Congenital rubella, toxoplasmosis, syphilis, herpes simplex and Zika.
• Prematurity, very low birth weight, hyperbilirubinaemia requiring exchange transfusion, perinatal asphyxia, persistent pulmonary hypertension, extracorporeal membrane oxygenation, and neonatal aminoglycoside exposure.
• Craniofacial anomalies and inner ear malformations, including cochlear aplasia, incomplete partition types I to III, common cavity, cochlear nerve aplasia and enlarged vestibular aqueduct.

Auditory neuropathy spectrum disorder, in which otoacoustic emissions or cochlear microphonics are present with absent or grossly abnormal auditory brainstem responses, accounts for around 10 percent of permanent childhood loss and is over represented in neonatal intensive care graduates and in kernicterus. It requires a different management pathway, since amplification often disappoints.

• The infant fails newborn screening, which is how most cases are now identified.
• In the absence of screening, presentation is late: absent startle to loud sound, failure to babble or cessation of babbling by 6 to 9 months, absent response to name at 9 to 12 months, no single words by 15 months, no two word phrases by 24 months, and unclear speech at 3 years.
• Parental concern about hearing is a reliable indicator and should never be dismissed pending a screening result.
• Behavioural difficulty, inattention and apparent disobedience in older children.
• Motor delay, particularly delayed independent walking beyond 18 months, indicates associated vestibular loss and points to Usher type 1, CHARGE syndrome and severe inner ear malformation.

Examination for syndromic features

• Craniofacial: preauricular pits and tags, microtia, mandibular hypoplasia, cleft palate, coloboma.
• Skin and hair: white forelock, heterochromia iridis, café au lait spots, vitiligo.
• Neck: branchial fistulae, goitre.
• Eyes: cataract, retinopathy, coloboma, and a formal ophthalmology assessment in all cases.
• Cardiac: murmurs and an electrocardiogram for the prolonged QT of Jervell and Lange Nielsen syndrome in any child with profound congenital loss.
• Renal: blood pressure and urinalysis.
• Neurological and developmental assessment.

Screening and confirmation pathway

• Universal newborn hearing screening with otoacoustic emissions, followed by automated auditory brainstem response for those who refer, and automated auditory brainstem response as the first line test in neonatal intensive care graduates because auditory neuropathy is missed by emissions testing alone.
• The benchmark timeline: screening by 1 month, diagnostic confirmation by 3 months, and intervention by 6 months.
• Diagnostic auditory brainstem response with frequency specific tone bursts and bone conduction, giving ear specific and frequency specific thresholds.
• Auditory steady state response as a complement for severe to profound loss.
• Tympanometry with a 1000 Hz probe tone in infants under 6 months, since a 226 Hz probe gives unreliable results in the compliant infant canal.
• Behavioural audiometry as soon as developmentally feasible: visual reinforcement audiometry from 6 months, play audiometry from 2.5 years.

Aetiological investigation

• Congenital cytomegalovirus polymerase chain reaction on saliva or urine within the first 3 weeks of life. Beyond 3 weeks, testing the stored dried blood spot is the only way to establish congenital rather than postnatal infection. This test is time critical and is the single most commonly missed opportunity in the pathway.
• Genetic testing with a full hearing loss panel or exome sequencing, with formal genetic counselling. Yield exceeds 40 percent.
• Ophthalmological assessment in every child, both for syndromic diagnosis and because vision is the principal compensatory channel.
• Electrocardiogram in profound congenital loss.
• Renal ultrasound and urinalysis where branchio oto renal or Alport syndrome is suspected.
• Thyroid function and, where indicated, genetic testing for Pendred syndrome.
• Magnetic resonance imaging of the internal auditory meati and brain, which defines cochlear nerve presence, inner ear malformation and central pathology, and is essential before cochlear implantation. Cochlear nerve aplasia changes management entirely.
• Computed tomography of the temporal bones for bony anatomy, enlarged vestibular aqueduct, cochlear ossification and middle ear anatomy before implantation.

Management is multidisciplinary from the outset, involving audiology, otolaryngology, speech and language therapy, teachers of the deaf, genetics, ophthalmology and paediatrics.

Amplification

• Fit hearing aids within weeks of diagnostic confirmation, and by 6 months of age at the latest.
• Bilateral fitting with real ear to coupler difference measurements, since infant ear canal acoustics differ substantially from adult and unverified fitting leads to under or over amplification.
• Re verify at frequent intervals as the ear canal grows, initially every 3 months.
• Bone conduction devices on a softband for conductive loss from atresia or middle ear anomaly, from the first months of life.

Cochlear implantation

• Indicated for bilateral severe to profound loss with inadequate benefit from optimally fitted aids after a trial of 3 months, which may be shortened where the loss is profound and imaging confirms cochlear nerve presence.
• Implantation before 12 months of age gives the best language outcomes, and simultaneous bilateral implantation is standard where resources permit.
• Urgent implantation after bacterial meningitis before labyrinthitis ossificans obliterates the cochlea.
• Contraindications and cautions: cochlear nerve aplasia, for which an auditory brainstem implant is the alternative; and incomplete partition type III with a risk of cerebrospinal fluid gusher, which requires preparation.
• Vaccination against pneumococcus, meningococcus and Haemophilus influenzae type b before implantation.

Auditory neuropathy spectrum disorder

• Amplification often gives disappointing results because the deficit is neural dyssynchrony rather than audibility.
• Behavioural audiometry rather than auditory brainstem response guides management, since thresholds may be far better than the electrophysiology suggests.
• A proportion improve spontaneously in the first 12 to 24 months, particularly after hyperbilirubinaemia, so avoid irreversible decisions early.
• Cochlear implantation gives good outcomes where the cochlear nerve is present and the site of lesion is presynaptic.

Congenital cytomegalovirus

• Symptomatic congenital infection treated with valganciclovir 16 mg/kg orally twice daily for 6 months improves hearing and neurodevelopmental outcomes. Monitor full blood count for neutropenia every 1 to 2 weeks initially, then monthly, and monitor liver and renal function.
• Treatment of isolated asymptomatic infection with hearing loss alone is less well established and is decided case by case.
• Hearing loss may be delayed and progressive, so all infected children require audiological surveillance every 3 to 6 months until at least 6 years of age regardless of the initial screen result.

Enlarged vestibular aqueduct

• Counsel on progressive and fluctuating loss precipitated by head trauma and barotrauma.
• Advise helmet use, avoidance of contact sport and of diving, and prompt presentation with any sudden deterioration.
• Corticosteroids are frequently given for sudden drops, with uncertain evidence.

Habilitation and family support

• Speech and language therapy from diagnosis.
• Informed choice of communication modality: auditory oral, sign language, or a combined approach, supported without direction toward a particular option.
• Family sign language teaching where chosen.
• Educational support and personal frequency modulation systems.
• Genetic counselling including recurrence risk, which is 25 percent for autosomal recessive non syndromic loss.
• Psychological support for the family, and later for the child.

Surveillance

• Audiological review every 3 months in the first 2 years, then 6 monthly, and more frequently in progressive conditions.
• Continued surveillance in children who pass newborn screening but have risk factors, since delayed onset loss occurs after cytomegalovirus infection, meningitis, ototoxic exposure and with enlarged vestibular aqueduct.
• Annual review of the syndromic associations, particularly vision in Usher syndrome, renal function in Alport and branchio oto renal syndromes, and thyroid function in Pendred syndrome.