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LESSON 144

Infections and hearing

Year 2
Spring semester
Disorders of the Auditory and Vestibular Systems
Inner ear and retrocochlear disorders
Duration: 10:26

We explain the late-onset and progressive hearing loss of congenital cytomegalovirus infection, the severe unilateral loss caused by mumps, and labyrinthitis ossificans after bacterial meningitis. We also cover monitoring based on the JCIH 2019 risk indicators and the audiologist's role in urgent evaluation.

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Hello, and welcome to the AIHEAR Audiology Academy.
In this lesson, we learn about infections that cause hearing loss.
With congenital cytomegalovirus, mumps and bacterial meningitis as examples, we will see how audiological monitoring is planned.
Infections are an important group among the preventable or early-detectable causes of hearing loss.
Some infections pass to the baby before birth and cause congenital loss; the most common example is cytomegalovirus.
Viral infections such as mumps and measles can cause sudden loss in childhood.
Bacterial meningitis is one of the most important acquired causes of permanent, severe loss.
In this lesson, we look at these three examples and the audiologist's role in monitoring each of them.
Cytomegalovirus, or CMV, is a very common virus of the herpesvirus family.
In healthy adults it often causes no symptoms, but it can pass to the baby during pregnancy.
Infection acquired before birth is called congenital cytomegalovirus, or cCMV.
By common estimates, it occurs in about one in every two hundred newborns; the rate varies between populations.
Congenital CMV is the most common nongenetic cause of congenital sensorineural hearing loss.
Most infected babies show no symptoms at birth, so many cases go unnoticed.
Hearing loss is common in babies with symptoms at birth; studies report it in about one third to one half.
In babies without symptoms, the rate is lower, around ten percent.
But because asymptomatic babies are far more numerous, a large share of CMV-related losses comes from this group.
The loss can be unilateral or bilateral, and of any degree from mild to profound.
Its key feature is that it can begin after birth, fluctuate and progress over time.
So even a baby who passed newborn hearing screening can develop a loss later.
This example graph shows the average thresholds of both ears over time in a child with congenital CMV.
At birth, both ears respond at normal levels, and the baby passes newborn screening.
In the left ear, the loss begins after the first year and progresses step by step.
The right ear stays within normal limits during this period, so the loss progresses on one side.
This picture shows why children with congenital CMV need regular monitoring for years.
To diagnose congenital CMV, a sample usually has to be taken within the first three weeks of life.
If the virus is found in a later sample, it cannot be told whether the infection was acquired after birth.
Some countries offer targeted CMV testing to babies who fail screening; some programs screen all newborns.
For a diagnosed baby, the physician weighs the treatment options; early diagnosis gains time for this decision.
In its 2019 statement, the Joint Committee on Infant Hearing, or JCIH, recommends the first full audiological evaluation by three months.
After that, monitoring at least once a year until age three is recommended; the interval is shortened for family concern or findings.
Congenital CMV can affect not only the cochlea but also the vestibular system.
Studies report dysfunction of the otolith organs and canals in a large share of children with CMV.
This can contribute to delays in motor milestones such as sitting and walking.
When hearing and balance findings are monitored together, the child's development can be better supported.
When the diagnosis is considered late, the virus can be sought in dried blood spots taken as a newborn; this is not available everywhere.
Mumps is a viral infection known for swelling of the salivary glands.
A rare but severe complication is a sudden sensorineural hearing loss.
The loss is usually unilateral and often profound; in the example audiogram, the right ear looks like this.
Reported rates vary widely, from one in a thousand to one in twenty thousand people with mumps.
The loss is often permanent; because it affects one ear, it may go unnoticed in a child for a long time.
The measles, mumps and rubella vaccine has greatly reduced how often this loss occurs.
Other infections that can cause congenital loss are also known as the TORCH group, from their initials.
Congenital rubella was an important cause of congenital deafness before the vaccine era.
Toxoplasmosis and congenital syphilis are also infections linked to hearing loss.
Herpesviruses and the Zika virus are also among the JCIH 2019 risk indicators.
Babies who had one of these infections are enrolled in monitoring even if they pass newborn screening.
Meningitis is inflammation of the membranes around the brain and spinal cord; the bacterial type is the most dangerous for hearing.
Studies report permanent sensorineural loss after meningitis in about five to thirty percent of cases.
The loss is most common after pneumococcal meningitis.
The infection usually reaches the inner ear through the cochlear aqueduct or the internal auditory canal.
The loss is usually bilateral and often severe or profound.
Vaccines against pneumococcus and similar bacteria have reduced this risk.
After meningitis, inflammation of the inner ear, called labyrinthitis, can first fill the cochlear spaces with fibrous tissue.
This tissue can then turn into bone; this is called labyrinthitis ossificans.
Ossification usually begins in the basal turn, near the round window.
The process can begin within weeks; as it advances, inserting a cochlear implant electrode becomes harder.
This is why severe loss after meningitis is one of the situations that require urgent referral to an implant team.
Whether ossification is present, and how far it has gone, is assessed by the physician with imaging.
Hearing evaluation after meningitis should not be put off.
JCIH 2019 recommends a diagnostic audiological evaluation no later than three months after confirmed bacterial or viral meningitis.
Because of the risk of ossification, many centers do this evaluation much sooner, before discharge if possible.
If a severe loss is found, the child is referred without delay to an ENT physician and a cochlear implant team.
Even if hearing is normal on the first test, monitoring is planned because the loss can change.
A clinical tip: when booking a child who has had meningitis, do not push the test weeks into the future.
If the loss is severe, there may be limited time to reach the implant team before ossification advances.
Without behavioral testing, a quick first evaluation uses the auditory brainstem response, or ABR, and otoacoustic emissions.
Sending the result to the physician the same day markedly speeds up the referral process.
In the history, the audiologist asks about infections during pregnancy, the newborn period and childhood infections.
They make sure children with risk indicators stay in monitoring, even if they passed screening.
In urgent situations such as meningitis, they carry out the evaluation without delay.
They tell the family to come in right away if they notice any change in the child's responses to sound.
For diagnosis and treatment decisions, they work with the physician and, when needed, the implant team.
Congenital CMV is the most common nongenetic cause of congenital sensorineural loss.
CMV-related loss can begin after birth, fluctuate and progress, so regular monitoring is needed.
Mumps-related loss is usually unilateral and profound.
After bacterial meningitis, hearing is evaluated promptly; labyrinthitis ossificans can limit the time available for an implant.
Test yourself: Why should hearing be evaluated promptly after bacterial meningitis?
The correct answer is B: the cochlea can ossify.
If labyrinthitis ossificans advances, inserting a cochlear implant electrode can become harder.
In the next lesson, we will learn about third window syndromes and superior canal dehiscence.
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Prerequisites

LESSON 141 The audiologist in sudden hearing loss

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