Dear Dr. Donohue — I wrote to you three or four months ago about a nodule in my lung. What would cause it? — B.B.

Answer — "Nodule" is a word that's a stumbling block for many people. The direct translation of that word from Latin is "little knot." The knot you use to tie your shoe is a nodule. Lung nodules always arouse a suspicion of lung cancer, but most lung nodules arise for other reasons. It could be an old, healed infection or a harmless cyst; rheumatoid lung nodules can be seen with rheumatoid arthritis. A nodule can be a tangle of blood vessels, or it can be an old fungal infection that has become covered with calcium. A doctor makes sure that a nodule isn't cancer.

How does the doctor make that call? The patient's history helps. A nodule in the lung of a nonsmoker is less likely to be cancer than is a nodule in a smoker's lung. Very small nodules — those less the 4 mm, or about 1/4 of a dime, are not usually cancerous. Nodules one and a half to two times that size raise a greater suspicion of cancer and must be watched closely with repeat X-ray or scan.

A nodule's growth aids in determining its cancer potential. A nodule that hasn't changed size in two years can be safely assumed not to be cancer.

If your nodule is small and hasn't changed in size, the cancer possibility isn't great. If the doctor finds it impossible to judge the nature of a lung nodule, then he or she will ask for a biopsy. That's the ultimate test for assessing what the nodule is.

Dear Dr. Donohue — Please write about neuropathy. What causes it? Is there treatment? Can chemo medicines for cancer cause it? — L.V.

Answer — Nerves are the body's electrical grid. Information shoots over them from the brain to muscles and bones and tells them to contract so we can move and grab hold of things. These are motor nerves. Information also travels from nerves to the brain to give it information about the world around us and how we react to it. These are sensory nerves, which tell the brain if we are hot or cold or are hurting. Neuropathy — nerve damage — happens to motor nerves or sensory nerves or both. An affected motor nerve leads to muscle weakness. A common example is a foot drop. If the nerves to muscles that move the foot are damaged, raising the leg to take a step leaves the foot dangling. It causes a person to trip. That's a foot drop. A sensory nerve in the leg with neuropathy causes numbness or pain.

The Neuropathy Association will help you with more information. The association's website is www.neuropathy.org, and its phone number is 800-247-6968.

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Write Dr. Donohue at P.O. Box 536475, Orlando, Fla. 32853-6475.