Dear Dr. Donohue: Since starting to clip your articles, I haven't found any that deal with using adult stem cells for breakthrough treatments, such as repairing heart damage. Will you elaborate on what kind of damage adult stem cells help? Could they help if one needs an aortic valve replacement?
A.R. Stem cells are primitive cells that have the potential of spawning mature cells that carry out specific functions, like skin cells, liver cells, lung cells, heart muscle cells, and so on. Embryonic stem cells have the greatest potential for differentiating into any of the many varieties of cells that make up all body organs, structures and tissues.
Hematopoietic stem cells are recovered from the bone marrow and, to a lesser extent, the circulating blood. They have been and are being used to restore the bone marrow's capability of generating blood cells. They're often used in certain leukemias when the bone marrow is deliberately destroyed to disrupt the multiplying of leukemia cells.
A special kind of stem cell was produced only a few years ago. It's called an induced pluripotent stem cell. It is derived from a skin cell that has been genetically manipulated to perform very much like an embryonic stem cell. It has the capability of transforming into many other kinds of body cells. This kind of stem cell has been experimentally used in animals to restore heart function to hearts that have suffered a heart attack. Widespread use in the treatment of adults has not taken place.
At the present time, no stem cell-therapy has been used in replacing a heart valve. Stem-cell research proceeds at a rapid pace. Valve replacement might be feasible in the future, but it's not at the moment.
Dear Dr. Donohue: I would like to know the risk of having a stroke when a carotid artery has a blockage. I was told that doctors don't go by percentage of blockage now. How is the risk determined?
An obstruction in the carotid artery, the neck artery that supplies the brain with blood, is not the only cause of a stroke. A piece of a blood clot that has broken off of a main clot elsewhere in the body and been swept into a brain artery is another cause of stroke.
I mention this to keep it clear that a blocked carotid is but one risk for a stroke.
The doctors I know still use percentage of reduction in the interior of a carotid artery as a criterion of stroke risk. With a 60 per cent to 70 per cent or greater narrowing of the carotid artery, people benefit from the opening up of the artery, using a variety of procedures. Some experts feel that a 60 per cent narrowing requires only blood-thinning medication, such as Aspirin. Others feel that surgical removal of the blockage is indicated.
Other factors have to be considered: the patient's age, the patient's wishes and the patient's health problems unrelated to the artery problem.
Dear Dr. Donohue: I am an 85-year-old female, and my doctor has suggested a colonoscopy. I find it a degrading test. The doctor didn't say why I needed it. Should a woman my age have it?
The American College of Physicians recommends against screening colonoscopies for people 75 and older or for those people with a life expectancy of less than 10 years. Some add that screening can be stopped only if prior colonoscopies have been normal. No one I know recommends screening at 85.
Dr. Donohue is unable to answer individual letters, but he will incorporate them in his column whenever possible. Readers may write him at P.O. Box 536475, Orlando, FL 32853-6475.