Introduction

Newborn jaundice (yellowing of the skin and eyes) is not an uncommon phenomenon,¹ and is likely something most of us are familiar with, but when this jaundice is not treated, it can cause complications such as kernicterus. 

Kernicterus is a rare type of brain damage in newborn babies, which is caused by extremely high levels of bilirubin in their blood.^2,3 One of the most common and serious side effects of kernicterus is a particular type of hearing loss,⁴ which will be managed throughout the newborn's life into childhood and then adulthood.

However, this serious side effect’s impact on the person can be reduced if early detection occurs and proper treatment is carried out.⁵

Understanding the development of kernicterus

The levels of bilirubin are so high in newborns with kernicterus due to untreated or severe jaundice.^2,3 Bilirubin is a waste product made by the liver,³ and when babies are born prematurely, their livers are not fully developed yet (alongside many other organs)^7,8, which is why kernicterus is more common in premature babies. It is also more likely in newborns of whom there is a specific difference in blood type compared to their mother’s or, even more rarely, in newborns who have certain specific medical conditions.⁹

These very high levels of bilirubin are toxic, and when they cross over the blood-brain barrier, they can accumulate in areas that are important for both hearing and the control of movement,damaging them. This is why kernicterus can lead to impaired movement and hearing.⁹

Hearing loss as a symptom of kernicterus

Hearing loss can be the consequence of several things, from ageing, noisy environments, viruses or genetic lotteries¹⁰, and hearing loss itself can be subdivided into several categories: sensorineural hearing loss, conductive hearing loss, and mixed hearing loss.¹¹ Kernicterus leads to the sensorineural type of hearing loss, which means that the organ of hearing (the cochlear or inner ear) or the auditory nerve is the location of the damage.

Auditory neuropathy spectrum disorder (ANSD): a specific impact

A more specific type of sensorineural hearing loss, to which kernicterus is a risk factor, is Auditory Neuropathy Spectrum Disorder (ANSD).¹² The auditory pathway (the pathway for hearing) is the most sensitive part of the central nervous system when considering high levels of bilirubin (i.e. kernicterus), and the part of the auditory pathway where damage occurs is typically the brainstem and cranial nerve VIII - this damage manifests as what is known as ANSD.¹³ Simply put, ANSD is where sound can be heard properly by the person, but the processing of the sound is not carried out correctly¹⁴ (as there is damage to the nerves involved in the auditory pathway).

If someone has ANSD,  they may struggle to understand speech in noisy environments or have trouble distinguishing between different sounds in words.¹⁴ In infants, this can be seen through more subtle things, for example:

• Lack of reaction to sounds
• Delay in speech development or babbling, or
• Inconsistent reactions/responses to noise^15,16

Diagnosis

Kernicterus itself becomes a possible diagnosis when signs are observed physically on the infant. These visible signs can be a range of things, such as (but not limited to): low muscle tone, feeding issues or lethargy. Once any of these signs are seen, and therefore kernicterus is suspected, measuring bilirubin levels can help either rule out (low bilirubin levels) or confirm (high bilirubin levels) the official diagnosis of kernicterus.¹⁷

Hearing tests   conducted on infants are different from those used for children, teenagers or adults. The tests specifically involved for infants  are:  

• Auditory Brainstem Response (ABR) -  where sounds are played into the baby’s ears via small earbuds, and electrodes pick up the responses from the brain
• Otoacoustic Emissions (OAEs) - where another type of sound is played into the baby’s ear and a small earbud detects how much sound bounces back to the machine. 

Across the globe, different countries have their own newborn hearing screening programmes,¹⁸ and these tests (and therefore results) can then detect any hearing losses early in order to optimise management and positive outcomes.¹⁹ It is important to remember that follow-up is very important, as some hearing problems do not show up immediately and can only present in the infant's test results at a later date.²⁰ 

Treatment and management

Kernicterus can be prevented if the newborn’s jaundice is treated early with phototherapy or exchange transfusion. As mentioned earlier, the concern for kernicterus only arises when jaundice is not treated and the bilirubin levels become toxic.

In the case of kernicterus happening and then causing hearing loss, the person will likely need either hearing aid(s) or cochlear implant(s) (depending on the level of hearing loss that has occurred). Alongside these devices, other therapies - e.g. family sessions - are recommended to be used as they play a critical role in the overall management of hearing losses. Some therapists who would be recommended to be part of the wider medical team involved in the infant’s care would be speech and language therapists, and they will work alongside doctors, nurses and audiologists to help make positive outcomes for all those affected by hearing loss.

Prevention

The best way to prevent hearing loss due to kernicterus in infants is to prevent kernicterus itself. Kernicterus can be prevented by monitoring newborns for jaundice, using both blood and clinical observations. The most crucial time for this monitoring is during the first few days of life.²¹ 

Extra attention should also be given to newborns who fall into the category of being more likely to develop kernicterus due to characteristics previously stated. The hope is that by identifying these at-risk infants, rapid treatment can be provided to prevent toxic levels of bilirubin from being reached, thereby preventing the consequence of hearing loss from the kernicterus. 

Prognosis and long-term outcomes

Several aspects of an infant’s life can be impacted upon due to hearing loss caused by kernicterus complications, these can include: speech, learning and social development. This is true for all children who have hearing loss;, however, the person usually adapts better and has an overall more positive outcome when the hearing loss is managed early and consistently, i.e. through hearing aids/cochlear implants and therapies.²² This level and type of ongoing support and education can ensure that children who are affected by hearing loss have fulfilling lives with a high quality of life.²³

Summary

Kernicterus is a condition that can be prevented by treating newborn jaundice early, and this can then prevent the serious complications that can happen due to kernicterus - one of these serious complications is hearing loss.

A crucial part of this prevention is knowing and recognising the early signs of jaundice, then ensuring proper treatment is administered and ensuring that follow-up (s) containing the relevant hearing test(s) are carried out.

If all aspects of the involvement of prevention, early diagnosis, and supportive care are optimised, then the negative impacts and consequences of kernicterus-related hearing loss can be reduced significantly.

Frequently asked questions (FAQs)

What is kernicterus, and how does it relate to jaundice?

Kernicterus is a rare type of brain damage that may happen if jaundice is untreated and becomes uncontrolled.

How does high bilirubin lead to hearing loss in infants?

When bilirubin gets to a high level, it becomes toxic, and when these toxic bilirubin levels cross the blood-brain barrier, the toxins collect in the areas of the brain that are responsible for hearing loss (and other functions).

Is hearing loss from kernicterus permanent or treatable?

As the hearing loss caused by kernicterus is classed as a sensorineural hearing loss, it is a permanent hearing loss; however, it can be managed well from an early age.

What management options are available for infants with kernicterus-related hearing loss?

The management options for infants with kernicterus-related hearing loss are hearing aid(s) and, if the hearing loss qualifies, cochlear implant(s). These would be prescribed and adjusted according to their hearing test results.

Can kernicterus be prevented, and how?

Kernicterus can be prevented if jaundice in infants (particularly during the newborn stage) is recognised early and treated early. Kernicterus cannot happen with jaundice, so if the jaundice is corrected by early intervention, then kernicterus is prevented.

What kind of support is available for families of children with hearing loss?

There is a wide range of support for families of children with hearing loss. The details of which vary from country to country, but to name a few organisations, there are: the National Deaf Children’s Society, Deaf Education through Listening and Talking, and the Council for Disabled Children. There’s lots of information from these organisations and others online, with physical resources available too. At the hospitals and specialist clinics associated with the child’s hearing loss journey, there is also other support available, and it can sometimes even involve group meetings.