DEAR DR. DONOHUE: My husband’s myasthenia gravis has been with him almost 50 years. Would you say a few words about this disease? Many people know nothing about it. – R.S.

ANSWER: Myasthenia (my-as-THEE-knee-uh) gravis is unfamiliar to most people until they come down with it or learn of a friend or relative who has it. Then they discover that the world is populated by many myasthenia patients.

Muscles contract when they are activated by nerve signals. The signal from nerves is the chemical acetylcholine. It sails across the gap between nerve and muscle and lands on the muscle’s docking stations, called receptors. When secured on the muscle receptor, acetylcholine turns on the switch for muscle activation.

In myasthenia, muscles’ docking stations are blocked by antibodies. These antibodies come from a misfiring immune system.

Without acetylcholine, arms and legs weaken. Droopy eyelids are common. So is double vision, because eye muscles cannot coordinate the proper alignment of the two eyes. Speech can become slurred, and swallowing can be a serious problem.

Medicines that boost the supply of acetylcholine keep muscles working. Other medicines directed at the immune system can stop the production of disruptive antibodies. The thymus gland, located in the upper chest, is a gland seldom mentioned. It influences normal functioning of immunity. If the thymus gland has a tumor – a thymoma – removal of the tumor can end myasthenia symptoms. Even without a tumor, sometimes thymus-gland removal restores normal nerve-muscle function.

If you have access to a computer – and most communities have libraries that provide such access – home in on the Myasthenia Gravis Foundation’s Web site, www.myasthenia.org. You’ll find a storehouse of information there.

DEAR DR. DONOHUE: I have been careful to drink milk every day. I had a checkup in the hospital and was shocked to learn I have osteoporosis. I am 84. I read your advice to drink milk to prevent osteoporosis. What else can I do to beat it? – E.T.

ANSWER: How much milk do you drink each day? Women of your age need 1,000 to 1,500 mg of calcium daily. An 8-ounce glass of milk has 300 mg. To get the recommended daily allowance, therefore, you would have to drink three to five glasses of milk. Most people do not drink that much milk, and they have to turn to calcium supplements to make up the deficit.

You cannot focus on calcium alone. Vitamin D is essential for calcium absorption, and women and men age 50 and older need 400 IU of that vitamin every day. If they are older than 70, 600 IU is the recommendation. Some doctors feel that 800 IU is desirable, an amount well within the safety limits of this vitamin.

Exercise is a must. Walking fits the bill.

Many women, in spite of calcium, vitamin D and exercise, still need an extra boost to keep their bones strong. Alendronate (Fosamax) and risedronate (Actonel) are examples of drugs that are quite effective in building strong bones. Both come in a tablet size that needs to be taken only once a week. Ask your doctor if either is a medicine you could use.

DEAR DR. DONOHUE: I am a 17-year-old girl with a pierced bellybutton. My parents told me that I was not allowed to get it done until I was 18, so I have been hiding it for one year. In the past month, it seems to have been infected. It has a bulge that excretes pus and is very tender. Is there any chance that the infection will go away on its own? – A.J.

ANSWER: You can bet your bottom dollar that a tender bulge that exudes pus is an infection. When skin and the tissues beneath are infected and when they have a foreign body in them like a bellybutton ring, infections almost never go away on their own. Usually the foreign body – i.e., the bellybutton ring – must be removed and antibiotics prescribed. Don’t waste any time. See the family doctor tomorrow – or today if you can.

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.