DEAR MAYO CLINIC: Ever since I had my son, I tend to worry whenever he gets ill, so I try to educate myself on different viruses and autoimmune disorders. I recently came across encephalitis. What is it? What are some of the warning signs? And how is it treated?

ANSWER: It's normal to worry as a parent. However, encephalitis is a rare disease. The word encephalitis means swelling (often inflammation) of the brain. Early signs can include the sudden onset of headache, fever and frequent seizures. Patients will often develop cognitive problems such as memory loss, hallucinations and confusion — sometimes not knowing what time of day it is or what year it is. A number of patients can develop problems walking, abnormal movements, fluctuating blood pressure and potential loss of consciousness. It can be a very challenging time for everyone involved.

What causes encephalitis is two-pronged. For some patients, infections from bacteria or viruses can cause their illness, which is called infectious encephalitis. For other patients, their own immune system causes the illness when immune cells attack the brain by mistake, which is called autoimmune encephalitis. Family history or genetic predispositions can play a part in autoimmune encephalitis, but it is not spread from person to person.

Encephalitis is treated depending on the cause. If you have an infectious cause, you usually receive drugs that try to eliminate the virus, such as antiviral drugs. This can be very successful, especially if given early on. In patients who have autoimmune forms of encephalitis, the body's immune system is overactive. Suppressing the immune system can greatly improve the patient's symptoms.

Once immunosuppressive treatment has begun, especially if it can be started early in the diagnosis, many patients make dramatic improvements. However, despite those improvements, many patients are left with remaining symptoms such as memory problems and sleep disturbances. There are currently no preventive measures or vaccines for these illnesses, but there is hope in research.

Our research is essential because we're trying to better understand how the patients present their illness to health care professionals and, therefore, how they can be diagnosed accurately. We hope to improve recognition of the disease, better understand how to measure the disease, how to measure improvement in an individual patient, and then be able to answer the ultimate question that all our patients want to know: "Why did this happen to me?"

Over the last 10 or 15 years of both doing research and seeing hundreds of patients with autoimmune encephalitis, we've improved our understanding of which patients should receive which treatments at which times, and we've understood much more about how to begin to estimate and explain to the patient, their relatives and caregivers what we think might happen in the future.

— Sarosh Irani, B.M.B.Ch., D.Phil., Neurology, Mayo Clinic, Jacksonville, Florida

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