The tests listed below can find the reason for a child’s deafness in 40% to 50% of cases. For the other 50% to 60% of cases, it is not possible to find out why a child is deaf. If it is not possible to find out the cause of your child’s hearing loss, it may be helpful for you to know what did not cause it.
Doctors sometimes may suggest tests on other parts of your child’s body, like the kidneys or heart, to help identify the cause or rule out certain conditions that can be associated with hearing loss. Hearing loss can be part of a ‘syndrome’. (Syndrome is a medical term meaning a collection of symptoms or signs that commonly appear together).
It is important to know about any associated medical conditions so you can consider appropriate treatment or ways of managing the hearing loss or condition. However, these conditions are relatively rare in deaf children and extremely rare in the population as a whole.
As with many medical procedures, you may be asked to give your written permission for some of the tests first. Most of the tests are not urgent. Speak to your doctor if you have any concerns. It is important that you understand why the tests are needed and are comfortable with your child having them.
The doctor will take details of your child’s medical history. This will include questions about the pregnancy, including any medication that was taken during the pregnancy and the mother’s health before, during, and after the birth.
The doctor will ask you about your child’s immunisations (routine baby jabs). In toddlers and older children, the doctor will ask about your child’s development (including speech, language and milestones such as when your child was sitting, walking and so on). The doctor may also ask about whether your child has:
All of these factors are important when investigating the cause of hearing loss.
The doctor will also ask about the hearing of other family members, on both sides of the family.
The doctor will look at your child’s head and face area and may also take some measurements. The doctor will also look at your child’s neck, skin, nails, arms, legs, chest, abdomen (tummy), eyes, mouth, palate (roof of the mouth) and ears. They are looking for any minor differences or signs (for example, tiny holes in the skin known as ‘pits’),that may help to diagnose the cause of the hearing loss. The doctor will assess your child’s development in relation to the expected ages and stages.
The doctor may ask close family members to have a hearing test, known as an audiogram.
Imaging is a general term covering different ways of looking at parts inside the body (such as bones or major organs) and how they are working.
The doctor uses an MRI (magnetic resonance imaging) scan or a CT (computerised tomography) scan to look at the structure of the ear and hearing nerve as well as other parts of the body that may be associated with the hearing loss. Both types of scans are commonly used with children who have a hearing loss.
MRI scan
An MRI scan will show soft tissues including the brain and hearing nerve. It will show if the hearing nerve has developed normally. MRI scans use magnets and radio waves to produce detailed pictures of the inside of the body. There are no known side effects associated with this type of scan. An MRI scan can be carried out on a child from birth, but you should be offered a choice of when the scan is done. If it is important for your child to have the scan, the doctor will explain this to you.
CT scan
A CT scan will show the bony parts of the ear including the ‘ossicles’ (the three tiny bones in the middle ear) and the ‘cochlea’ (the inner ear). A CT scan will show if the bony parts have developed normally. A CT scan involves exposing your child to radiation in the form of X-rays. The level of radiation used is kept as low as possible to prevent damage to body cells, and the amount of radiation your child is exposed to depends on the number of images taken. It is generally accepted that there is little risk to health from one scan, but with repeated tests, there is a risk that the radiation may damage body cells. There is only a risk if your child has a high number of x-rays or scans. The earlier in life your child is exposed to radiation, the greater the risk. You and the doctor may prefer to wait until your child is a little older. Your child’s doctor will discuss this with you and answer any questions you may have.
Your child will need to be absolutely still for the time it takes to do a CT or MRI scan. Very young babies may be able to have these scans while they are asleep. Each hospital will have its own procedure, and your doctor will explain this to you. It is generally recommended that children under four years of age have a general anaesthetic when CT and MRI scans are being done.
Although modern anaesthetics are extremely safe, there are small risks associated with having an anaesthetic and your doctor should explain these to you. The risks of having an anaesthetic reduce as the child gets older. Usually, children over the age of five can lie still for the scan without needing a sedative or anaesthetic.
Renal ultrasound
A further type of scan that may sometimes be used is a renal ultrasound. This is a scan that uses sound waves to create images of the kidneys. It is similar to the scans used during pregnancy. It is only likely to be used to rule out a rare syndrome or if there is a family history of kidney problems. There are no risks associated with this type of scan.
Your doctor may recommend that one or more of the above scans are done at
an early stage, for example, if:
In these examples, your doctor will need to look closely at the structure of the cochlea (inner ear) and hearing nerve to be able to give you advice on possible management or treatment options.
An ECG is a recording of the rhythm and electrical activity of the heart. There is a very rare syndrome linking severe and profound hearing loss to a heart problem. If this heart problem is detected it can be treated.
Depending on your child’s and your family’s medical history, your doctor may advise an ECG for a small number of children with severe to profound hearing loss to help rule out this condition. There are no risks associated with having this test.
Depending on your child’s and your family’s medical history, the doctor may ask for one or more routine blood and urine tests. These tests can help doctors to identify the cause of the hearing loss.
An example of a blood or urine test your child may be offered is an infection screen. An infection screen is used to look for certain infections that sometimes result in hearing loss. Some of these tests will give useful results only if they are carried out in the weeks or months shortly after your child’s birth. When the child is older, an infection screen may give a negative result and rule out an infection being the cause of the hearing loss. However, a positive result later in life may not give useful information as your doctor could not prove that the infection was present at birth and so caused the hearing loss.
There are several infections that can cause hearing loss in babies if the mother contracts them when pregnant. The most common infection causing babies to be born with hearing loss is CMV (cytomegalovirus). CMV is very common in the general population and does not normally cause any illness. However, it can affect the baby if the mother catches it while pregnant. About one baby in a hundred is born with CMV and some of these babies can be affected by it. CMV can cause deafness or, very occasionally, it can affect a child’s development.
The small sample of blood that was taken for your baby’s ‘heel prick test’ in hospital can also be used to find out if your baby was exposed to CMV before they were born. These newborn hearing screening cards are stored until your child is 28 years old so the dried blood on the card can be tested for CMV at a later stage.
Hearing loss following CMV infection can sometimes get worse over time. If a young baby is found to have the CMV infection, it may be possible to give treatment that may prevent the hearing loss from increasing. In Australia, this treatment is generally only offered to babies if there is life- or sight-threatening disease as the treatment causes bone marrow suppression and requires 6 weeks of intravenous therapy. You are advised to consult with your paediatrician and discuss your options.
Less common infections that can cause hearing loss include rubella (German measles), toxoplasmosis and syphilis. Your doctor will be able to give you more information about these infections. All the blood tests are usually done using one blood sample.
All children learn from what they see and hear around them. Children with hearing loss rely on their eyesight even more than other children do. Up to 40% of children with sensorineural hearing loss also have an eye problem. This may simply mean the child will need to wear glasses when they are older, but an eye test can also help to diagnose a syndrome associated with hearing loss. As babies can’t tell us what they can see, a developmental assessment of the eye is done to make sure the eyes are healthy. Sometimes special eye tests are used. Your ophthalmologist (eye doctor) will discuss this with you if necessary. It is recommended that all children diagnosed with a hearing loss are referred for an eye test and have regular eye tests throughout their childhood.
Just as children inherit features such as hair colour or eye colour from their parents, sometimes hearing loss is inherited. Most people have 23 pairs of chromosomes – microscopic structures that contain genes – in each of their cells. In each pair of chromosomes, one is inherited from the mother and the other from the father. Sometimes there is a change in a particular gene that results in a different characteristic, for example hearing loss. The change in a gene is known as a ‘fault’ or ‘mutation’.
Genes can work in different ways. Sometimes a child only needs to inherit one gene, from either their mother or their father (dominant inheritance) to have that particular characteristic.
Sometimes the child would need to have the same gene passed on from both parents in order to have a condition (recessive inheritance).
Some people are known as ‘carriers’. This is where they have the gene but don’t have the characteristic. So a person who is a carrier for hearing loss would have the gene but would not have a hearing loss themselves. However, they can pass it on to their children.
Sometimes a gene mutation is a ‘one-off’ that simply happened by chance. This means that, although the hearing loss has a genetic cause, it has not been inherited. However, the gene mutation could be passed on to future generations.
It is impossible to summarise in this article all the different areas that could be covered in genetic counselling. If your child’s hearing loss could have a genetic cause, you should be given the chance to discuss this with a trained genetics counsellor. Genetic counselling gives families information about:
Some families find it helpful to know whether the hearing loss and any other medical condition were inherited. Other families prefer to wait until their children are grown up and able to decide for themselves.
You may be offered a genetic test. This will involve your child, and possibly other family members, having a blood test.
The blood sample will be used to look for the gene or genes known to be involved with hearing loss. All the genes related to hearing loss have not yet been identified and for most, there is no routine test. This means that even if the hearing loss is inherited, it may not be possible to confirm this with a genetic test. Genetic testing is constantly improving and new genetic tests become available over the years. Your doctor may be able to offer new genetic tests in a few years if all your previous tests were negative.
About 50% of children with permanent hearing loss have a genetic cause. In about 30% of children with a genetic hearing loss, the hearing loss is part of a syndrome. That is, there are other features associated with the hearing loss. Again, some of these syndromes can be confirmed with a genetic test, but many cannot.
Some children have a rare genetic hearing loss that can get worse if they are given certain medications. It is possible to have a genetic test to identify whether they have this gene. If they do, then this information will help inform you and your doctor if, in the future, your child needs treatment. Your doctor may recommend that this test is done at an early stage depending on your child’s history.
Your doctor (GP, paediatrician or ENT specialist) may refer you to a clinical geneticist or a genetic counsellor. Alternatively, they may discuss genetic testing with you themselves. The availability of genetic services varies across Australia. The service is sometimes based in specialist paediatric or obstetric departments in hospitals. If you want to ask more about genetic testing, you can ask your GP, paediatrician or ENT specialist to refer you to your local clinical genetics service. Your doctor will discuss with you if this is appropriate.
Some or all of the above tests will be offered to your child. Your doctor will give you more information that will help you decide whether you want your child to have the available tests and the best time for the tests to be carried out.
Test results that may offer immediate benefit to your baby are best done at an early stage, for example when the infection screen is carried out.
Some tests (for example, some routine genetic testing) will not offer an immediate or direct benefit to a baby and may be delayed until a later stage. Your doctor will tell you if particular tests should be done (for example, if your doctor suspects that your child’s hearing loss is part of a syndrome). You and your doctor can use this information when planning how to manage the hearing loss and any associated condition in the future.
Most of the tests are not urgent. It is important that you feel comfortable with your child having them. Discuss any worries with your doctor. Your doctor should be able to answer any questions you have.
References
Additional reading | Childhood Hearing Australasian Medical Professionals (CHAMP) Network
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