74 Paediatric Hearing Assessment
Assessing hearing in children requires experience, expertise and skill. It requires close teamwork as, under the age of 4 years, the assessment often requires two testers who must have good mutual understanding. The importance of assessment cannot be emphasised enough as early detection of hearing loss in children leads to more favourable management outcomes. This is because in pre-lingual children, the crucial window for speech acquisition is finite. It is important that the child with a hearing loss is managed by appropriate amplification as early as possible. This is the basis of the newborn hearing screening programme designed to pick up a hearing loss in a child soon after birth. In post-lingual children, a hearing loss may generate a negative emotional and behavioural reaction and early intervention is also recommended and helpful. Hearing assessment in children is performed by behavioural audiometry or objective audiometry. Universal newborn hearing screening (UNHS) employs automated objective audiometry.
74.1 Rationale for Hearing Assessment in Children
Epidemiologically, congenital hearing loss is a significant morbidity affecting 1.06:1,000 live births and for late-onset or acquired hearing loss the prevalence is 1.65 to 2.05:1,000 up to 9 years. Late-onset congenital hearing losses and acquired hearing losses are thus important and indeed one of the commonest conditions in childhood. In all cases, early intervention after diagnosis from a multidisciplinary team is essential as hearing loss is inexorably linked to the development and behaviour of the child. It has been shown that early intervention leads to better speech development in pre-lingual hearing losses and hastens positive social and mental development. For post-lingual children, early intervention can preclude many negative emotional reactions and improve worsening academic grades as a result of the hearing loss.
74.2 The Newborn Hearing Screening Programme
Many countries in the world have adopted a universal newborn hearing screening programme either mandated by federal government or by state. In the United Kingdom, this is a government initiative.
An automated transient otoacoustic emission test (AOAE) is carried out in all newborns which the machine scores as a pass or a fail in the form of a clear response (CR) or a no clear response (NCR). A pass is a discharge unless there are reasons for targeted surveillance. An initial failure leads to a second test. If the child fails the second test, it is referred for an automated auditory brainstem response test (AABR). A pass in this test is a discharge again, unless complicated by risk factors demanding subsequent targeted surveillance. A failure, however, necessitates full diagnostic auditory brainstem response (ABR) and otoacoustic emissions (OAEs) under natural sleep in the local audiology unit. The automated tests are neither 100% sensitive nor specific; subsequent normal hearing can still be found in some cases.
Some children who have passed their newborn hearing screening may still be reappointed for behavioural audiometry at 8 months after birth for targeted surveillance in the presence of a risk factor—examples include ototoxic medication, prematurity, some infections, meningitis and genetic syndromes.
The diagnostic ABR also establishes hearing thresholds for effective prescriptive fitting of digital amplification within a maximum of 6 months after birth for maximum outcome or in case of profound hearing losses referred for cochlear implantation. At the same time, the child is investigated thoroughly from an aetiological point of view. Detecting a cause is an important management process. The moment a child’s hearing loss is diagnosed, a full multidisciplinary process is set in motion that involves the audiovestibular physician, the otologist, the audiologist, the speech and language therapist, the paediatricians, the sensory services and the parents.
The protocol for premature children or children admitted to the neonatal intensive care unit (NICU) is slightly different. They undergo both AOAE and AABR to pick up auditory neuropathy spectrum disorder (ANSD) which is a condition characterised by normal cochlear function with abnormal auditory brainstem responses and management instituted accordingly.