Audiology and hearing-test interpretation — formative SAQs

SAQ 1 (10 marks)

A 5-week-old infant is referred to the clinic after a referred newborn hearing screen on the right ear. The diagnostic testing shows robustly present otoacoustic emissions at all frequencies on both ears, but the auditory brainstem response on the right shows no reproducible wave V even at high stimulus levels, with a preserved cochlear microphonic. [11] [1]

1. State the most likely diagnosis and the audiological findings that support it. (3) [11]
2. Explain why an otoacoustic-emissions-only newborn screen would have failed to detect this condition. (3) [11] [2]
3. Outline the management of this child, including the role of amplification and the team involved. (4) [11] [1]

Model answer — SAQ 1

(1) Diagnosis and supporting findings (3). The most likely diagnosis is auditory neuropathy spectrum disorder (ANSD). The supporting findings are the dissociation between the otoacoustic emissions and the auditory brainstem response: the OAE are robustly present, confirming that the cochlear outer hair cells are functioning; the ABR on the right is absent with no reproducible wave V even at high stimulus levels, confirming that the auditory nerve or its synapse is not conducting a synchronous response; and the cochlear microphonic is preserved, which rules out a severe outer hair cell (cochlear) loss and localises the failure to the neural-synaptic part of the pathway. This pattern is the signature of ANSD and is seen, for example, in OTOF-related hearing impairment. [11]

(2) Why OAE-only screening fails (3). Otoacoustic emissions report only on the cochlear outer hair cells — the biological amplifier at the sensory end of the pathway. In ANSD the outer hair cells are intact, so the OAE are preserved and an OAE-only screen reports a pass, while the neural pathway that actually carries the signal to the brain is impaired. The ABR is the only screening modality that interrogates the whole pathway from cochlea to brainstem, so a two-stage protocol that includes automated ABR (aABR) is required to detect ANSD. This is the structural limitation of OAE-only screening and the reason most modern programmes use a two-stage OAE then aABR protocol. [11] [2]

(3) Management (4). The child is managed by a multidisciplinary team led by paediatric audiology and ENT, with the family enrolled in early intervention services. The management diverges from a typical sensorineural loss because amplification may improve detection without restoring the intelligibility of speech — the hallmark difficulty of ANSD is that sound is heard but not encoded for timing. The team weighs hearing aids calibrated to the ABR thresholds, FM or remote-microphone systems to improve the signal-to-noise ratio, and, where speech perception remains poor despite a trial of amplification, cochlear implantation, which can be highly effective when the lesion is at the synapse (as in OTOF-related ANSD). The child needs ongoing behavioural and electrophysiological monitoring, and the family needs honest counselling that the trajectory and the benefit from each intervention are individualised and audiology-led rather than protocol-driven. [11] [1]

SAQ 2 (10 marks)

A 3-week-old infant is confirmed to have congenital cytomegalovirus (cCMV) infection identified on the salivary PCR. The newborn hearing screen (OAE then automated ABR) was passed on both ears, and a diagnostic ABR at 3 weeks shows thresholds within the normal range. The parents are reassured and ask whether the baby's hearing is now guaranteed. [6] [2]

1. State whether the normal ABR at 3 weeks excludes future hearing loss, and justify your answer. (3) [6]
2. Outline the audiological surveillance plan you would put in place for this child. (4) [6] [1]
3. Explain the place of valganciclovir in this child, and who supervises it. (3) [6]

Model answer — SAQ 2

(1) Does the normal ABR exclude future loss (3). No. The normal ABR at three weeks confirms that there is no hearing loss today, but it does not exclude a future loss, because congenital cytomegalovirus characteristically produces progressive or late-onset sensorineural hearing loss. The virus damages the cochlea through a combination of direct injury to the stria vascularis and organ of Corti and an inflammatory vasculopathy, and this damage can declare itself months or even years after a normal early audiogram. A passed newborn screen is a point-in-time measurement, and cCMV is the single most important reason that a passed screen does not end surveillance. [6]

(2) Surveillance plan (4). The child is placed on a scheduled surveillance plan rather than a single reassurance. The plan is set by paediatric audiology and typically includes a baseline assessment at diagnosis and regular follow-up through early childhood — commonly at least every three to six months in the first year, then at longer intervals through the early years — using age-appropriate behavioural testing (visual reinforcement audiometry from around six months) supported by OAE and tympanometry as needed. The family is given written information, a named contact, and clear safety-net advice to return if they notice any change in the baby's response to sound, speech or behaviour. The child is also referred to paediatric infectious diseases, who coordinate the cCMV management and the decision on antiviral therapy, and to early intervention services so that any loss is acted on without delay. [6] [1]

(3) Place of valganciclovir (3). Valganciclovir is the antiviral used for symptomatic congenital CMV, where it improves hearing and developmental outcomes; the typical regimen is valganciclovir 16 mg/kg per dose orally every 12 hours for a 6-week course, with extended 6-month courses increasingly supported where hearing or developmental benefit is sought. In a child with a normal current audiogram but confirmed cCMV, the decision to treat is individualised and made by the paediatric infectious diseases team, weighing the risk of late-onset loss against the drug's adverse effects — the commonest significant adverse effect is neutropenia, which is usually reversible but requires monitoring of the full blood count, neutrophils and transaminases throughout treatment. The general paediatrician does not initiate valganciclovir alone; it is started and supervised in conjunction with infectious diseases. [6]