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Column originally published Feb 4, 2003

Encephalitis Is An Uncommon Complication Of Chickenpox Infection

Question: Several weeks ago, our ten-year-old son had chickenpox. When the blisters started to dry up, he complained of a severe headache that lasted several hours. The next day he went to school, and fell down a flight of stairs. We thought he was just careless. Then he started tripping and falling several times a day. One evening he fell on the ice when he tried to play hockey. As a result, he was admitted to the hospital. The paediatrician told us that he had encephalitis due to chickenpox. I have never heard of this, so I went on the Internet to look for more information. What I read terrified me. I found that children with brain tumour could have the same symptoms. The paediatrician reassured us that our son didn’t have brain tumour. He was right, our son started to improve shortly after. Can you explain how chickenpox can bring on this terrifying problem?


Encephalitis is an inflammation of the brain, and this can happen following chickenpox. It is not a common condition, that is why you couldn’t find much information on the Internet. Let me explain to you in more detail here.

Chickenpox is a very common childhood disease that I don’t need to describe very much. Almost everyone has had chickenpox while growing up. It is caused by a virus that spreads readily in daycares, schools, and among siblings. The virus is spread mostly through respiratory secretion, although live virus is also present in fresh blisters or pox lesions on the skin. After an incubation period of 7 to 21 days, when the virus slowly multiplies in the throat, the clinical disease begin with fever followed by the typical blisters.

Under normal circumstance, new blisters appear every day for several days. After 5 to 7 uncomfortable days, the blisters would dry up, and the problem is over. Most children do not require any medical attention. Medicine like acetaminophen or ibuprofen can keep the fever under control. Warm baths and Calamine lotion can reduce skin irritation, and provide some comfort to these children.

The most common complication is secondary bacterial infection. Because of itchiness caused by inflammation in the blisters, children naturally scratch with their finger nails. Parents know how difficult it is to keep these little fingers and nails clean. Bacteria can infect inflamed tissues exposed by scratching. Most of the time these bacterial infections are mild and can heal without treatment. However, in recent years, Streptococcal infections following chickenpox are responsible for many serious complications and even death of some young children.

A much less common complication of chickenpox infection is inflammation of the brain, also called encephalitis. Most of the time, this occurs several days after the onset of chickenpox, when blisters are beginning to dry. It also coincides with the time when antibodies are produced to fight the virus. Although the exact mechanism of encephalitis is still unknown, it is most likely related to the body’s natural defence causing inflammation in the brain.

The observation of unsteady gait and falling suggests that the inflammation occurred mostly in the part of the brain called cerebellum. This part of the brain controls our balance and equilibrium. That is why the most obvious symptoms are loss of balance and falling easily. However, it is not uncommon to have other symptoms like lethargy, headache, and difficulty in concentration. The inflammation can be more extensive than in the cerebellum itself.

Fortunately this kind of encephalitis is generally mild, and these children almost always recover completely, within days or weeks. If the problem was due to brain tumour, one would expect your son to deteriorate with time instead of steady improvement.

I should mention another serious complication of chickenpox here for other parents and readers. You may have heard of Reye Syndrome. This can happen to children with chickenpox or influenza, and being given aspirin to control their fever. The liver in these children can become severely damaged, sometimes resulting in death. That is why aspirin should never be given to children with chickenpox and influenza.

In the last few years, chickenpox vaccine was licensed in Canada, and is provided free of charge by some provinces across Canada. It is a very effective vaccine, with extremely low chance of side effect. Unfortunately many parents are still unaware of the benefit of this vaccine. Many serious complications of chickenpox can be avoided by vaccination.

Finally, I would like to say a few words about medical information on the Internet. Most parents are not aware that there is a lot of mis-information out there. What is written on a web site does not guarantee that it is accurate. Furthermore, searching for possible diagnosis from one or two symptoms can lead to unnecessary stress. Many medical conditions have overlapping symptoms. That is why consulting a physician is still the best avenue when your child is sick. Your physician can put together the history and physical findings, with the assistance of various tests, and provide you with the most likely diagnosis and management plan. This does not imply parents should not seek information on their own. Many hospitals have medical resource centres that can assist people in their search for good medical information that is both useful and reliable.