Q: Can you please explain the difference between sleep apnea and narcolepsy? My friend who is rather obese was just tested and told that he may have narcolepsy.

Is there a way to control it? Does he have to stop driving? We are all worried. — Sasha

A: I do not know how old your friendis, but unlike sleep apnea, narcolepsy is rarely diagnosed after 40. Both diseases cause excessive day somnolence, but this is really just about the only feature they have in common. Narcolepsy affects men and women equally. It is more common in certain parts of the world (Japan much more than the United States). It may run in families. The main problem a person with narcolepsy experiences is a sudden attack of sleep, regardless of where the person is or what they are doing. As you have described, there is also sleepiness during the day. Another unusual characteristic is called cataplexy. It is sudden, uncontrollable loss of muscle tone. This experience is usually brought about by an intense emotion, often a positive one like laughter. It may result in a fall or injury. About 70 percent of people with narcolepsy experience these "attacks."

Some people have them only a few times a year; others have them a few times a week. The third phenomenon is periods of sleep paralysis — the inability to speak or even move — around the time one falls asleep. They last from seconds to minutes, and can be extremely scary, at least initially. Believe it or not, all of us

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experience sleep paralysis to some extent. It is one of the characteristics of a deep part of our normal sleep cycle, called REM sleep (Rapid Eye Movements, which also happens at the same time). However, people with narcolepsy are still awake and aware when paralysis happens.

Quite often patients with narcolepsy have hallucinations, usually seeing things which are not there, and they will have them when they are falling asleep or waking up. Again, healthy people occasionally will have disturbances like that as well. Finally about 40 percent of patients have "automatic" behaviors during sleep, like talking, moving, even eating. They are not aware of these behaviors because they are in the state of sleep.

This very peculiar illness is poorly understood. Doctors know that there is a problem with certain chemicals in the brain in people with narcolepsy. Both sleep apnea and narcolepsy can be diagnosed by staying overnight at a sleep center and having the entire sleep cycle monitored. In sleep apnea, the main problem is that due to a defective breathing process and/or some problems in the brain a person stops breathing during sleep — hence the name "apnea," which in Latin means "no breath." There may be just a few or very many episodes of not breathing, and once that happens there is less oxygen flowing to the brain.

For narcolepsy, certain medications may be helpful, but there is no cure. Stimulants like Provigil, certain antidepressants and the newest medication, sodium oxybate (Xyrem) can be used to limit the somnolence and cataplexy and paralysis attacks. Due to serious side effects, all medications must be used with the help of a sleep specialist. Understandably, certain activities, like driving, are dangerous for people with narcolepsy.

Now as far as the sleep apnea, once diagnosed, significant help can be achieved by using a special machine called CPAP (continuous positive airway pressure). This machine essentially forces air into the lungs at night, overcoming weak muscles. Weight loss, if sustained, can also be very effective as a treatment for sleep apnea because it often restores normal muscles' (especially neck muscles') anatomy and makes oxygen flow normally at night again. Occasionally, stimulant medications will be used in sleep apnea patients as well, to fight day somnolence.

As you can see, one can differentiate between the two diseases and the treatment is not the same. My suggestion is for your friend to ask his doctor very specific questions about his diagnosis. It was not clear from your letter if your friend actually has had a sleep study. If not, he definitely needs one as soon as possible. The most common reason for the day somnolence in adults and more mature patients are the side effects of medications (including over-the-counter) and a reversed sleep-wake cycle.

Dr. Beata Skudlarska is a Bridgeport geriatrician. Send questions to Bridgeport Hospital Center for Geriatrics, 95 Armory Road, Stratford CT 06614 or geriatricmd@aol.com.