DEAR DR. DONOHUE: I have a friend in his late 70s who has been diagnosed with encephalitis. It’s been about three weeks, and he still doesn’t recognize people. He speaks a little, but very softly. He can’t feed himself. Presently, he’s in rehab at a hospital. What is the cause of encephalitis? How is it treated? What are his chances for recovery? — R.K.

ANSWER: Encephalitis (in-SEF-uh-LIE-tiss) is brain inflammation, most often from a viral infection. Headache, fever and an altered mental state are its predominant signs. An altered mental state includes the inability to think clearly, confusion, lethargy and, in advanced stages, coma. Seizures, paralysis and speech difficulties are other signs.

About 20,000 cases of encephalitis occur yearly in the United States.

The number of different viruses that cause encephalitis is large, and each different strain of virus has a somewhat different clinical course.

I can’t tell you which virus caused your friend’s illness, but I’ll use the West Nile virus as an example. It first appeared in North American in New York City in 1999. Since then, it has spread to many states, Canada and Mexico. The virus is spread to humans through mosquitoes, and the peak spread of infection takes place in the summer and fall months. I am not suggesting your friend has West Nile infection. It’s an example of how many encephalitis viruses are spread and what they do to the brain. The aftermath of encephalitis is usually worse for older people. However, it is possible for everyone, even the elderly, to make a recovery.

There is a treatment for only a few encephalitis virus infections. The ones without a specific treatment require close monitoring of brain pressure, lowering of temperature and quick attention to any seizures that might arise. Your friend sounds as though the worst of his illness is over. That he is in rehab is a good indication that his brain is recovering. It takes a long time before complete recovery is achieved, and sometimes permanent disabilities remain.

DEAR DR. DONOHUE: My daughter has Tarlov cysts. Is there a cure? She has had them drained three times. She is 48 years old. — H.D.

ANSWER: Cysts are enclosed sacks containing liquid or gelatinous material. A Tarlov cyst is attached to a spinal cord nerve root in the lower back. Compression of those nerves by one or more cysts can bring on back pain or the pain of sciatica (back pain that runs down a leg).

From 5 percent to 9 percent of the population has some Tarlov cysts, but only a few have pain from them.

Doctors have devised many procedures to deal with painful Tarlov cysts. One is to drain them with a needle. However, the cyst or cysts usually return. Another is to fill them with cortisone by an injection. Cyst recurrence is possible with that therapy. Surgical removal with a microscope is another way of getting rid of them, and the recurrence rate is less. This is somewhat involved and delicate surgery.

If you or your daughter wants further information, go online to the Tarlov Cyst Association (www.tarlovcyst.net) or to the Tarlov Cyst Disease Foundation (www.tarlovcystfoundation.org).

I’m sure you’d like to know the cause. So would everyone in the medical field.

DEAR DR. DONOHUE: You look like one of the doctors who took three months to diagnose my celiac disease in 1968. By then, I was one of the walking dead. I was told to exclude oats as well as the other grains you mentioned. I decided to try oats again. In a week. I had a recurrence of symptoms. No more oats for me. — A.C.

ANSWER: People with celiac disease cannot digest gluten, a protein found in wheat, barley and rye. If they eat it, they can experience painful bloating, diarrhea and cramps. Oats do not have gluten. However, oats can be contaminated by the banned grains when oats are processed with machines that have been used to process those gluten grains. That means celiac patients have to be somewhat circumspect when it comes to eating oats. I wasn’t one of your doctors. I was in Vietnam in 1968.

Dr. Donohue regrets that he is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him or request an order form of available health newsletters at P.O. Box 536475, Orlando, FL 32853-6475. Readers may also order health newsletters from www.rbmamall.com.