How is encephalitis diagnosed?
When the doctor looks at your ill child, what he sees is like an out of focus picture. He can see that your child is sick but doesn’t know why. The questions he asks and the tests he undertakes make the picture clearer until ideally he can see clearly what is wrong with your child. Unfortunately, with encephalitis, despite all the tests that are available the picture never becomes completely clear.
There are some symptoms that are more usual in encephalitis but they are not always present. The most common symptoms are
Fever (a high temperature) – this tells the doctor that your child is fighting an infection. One of the body’s responses to an infection is to raise the body temperature which will slow down the bug that is causing the infection. Unfortunately too high a temperature in children can trigger a seizure (fit) and the immediate concern is to lower the temperature. So a high temperature makes the picture clearer but if the doctor stops there, assumes that your child has a common infection, and doesn’t look at other symptoms the actual diagnosis of encephalitis could be missed.
Vomiting, not eating, headache, miserable – these are all symptoms that are common with an infection but don’t really make the picture clearer or take the diagnosis further.
Aversion to bright lights, stiff neck – these symptoms indicate that the meniges (coverings of the brain) are infected. This happens in meningitis and in meningoencephalitis (the infection has spread from the meninges to the brain).
Seizures – seizures can be triggered by a high temperature but they can also occur in encephalitis without a high temperature. Seizures occur in more than 50% of encephalitis in children.
Confusion, sleepy, unresponsive – these are all symptoms of “lowered consciousness” and tell the doctor that the brain is involved in this illness. These symptoms make the picture much clearer and show that urgent action is needed.
There are many illnesses that can make a child ill and have obvious brain involvement. Tests are now needed to define the picture further and find the correct treatment.
Brain scan – CT scan – this brain scan uses a special x-ray machine. The scan will give a detailed image of the brain and will make the picture of your child’s illness clearer. However a CT scan will not give a clear diagnosis of encephalitis.
Brain scan – MRI scan – this scan uses radio waves to build up a picture of the brain. It gives more detail than a CT scan but your child has to keep very still so an anaesthetic may be given to make him / her sleep. It can make the picture very clear in some cases but not in all.
Lumbar puncture – fluid is constantly produces which bathes the brain, the fluid drains into the spinal cord from where it enters the blood circulation. The fluid cushions the brain from bumps, cools the brain and acts as a waste disposal system. Waste products from the working cells of the brain enter the fluid and are removed as the fluid drains from the brain. During a lumbar puncture, a needle is inserted into the spinal cord and a sample of fluid from the brain removed. It is examined for bugs which could be causing the infection and for substances that occur when the brain is being damaged in some way. This test can make the picture very clear in some types of encephalitis but not in all.
Blood tests – there are some illnesses that have a similar picture to encephalitis that can be clearly diagnosed by blood tests. It is important to discount these illnesses. Autoimmune types of encephalitis have an increased number of specific antibodies in the blood. If these antibodies are found the picture becomes clear and a diagnosis of autoimmune encephalitis is made.
EEG (Electroecencephalograph) – this test measures brain waves. It can detect an excess of fluid in the brain which is an indication of inflammation. Inflammation is usually in most types of encephalitis but not in all.
Adding together all the symptoms and tests can sometimes give a very clear picture of your child’s illness but in many cases the picture remains fuzzy making treatment a difficult decision for doctors.