By the way, doctor.

Author:Komaroff, Anthony L.

With Anthony L. Komaroff, M.D., Editor in Chief of Harvard Health Letter

Q. Is it possible to have one or more TIAs in the past four years and not have them show up in four MRIs?

A.: Transient ischemic attacks (TIAs) are symptomatically small strokes. Like a major stroke, a TIA occurs when a part of the brain suddenly fails to get an adequate supply of blood. The most common cause is blockage of an artery, usually by a piece of atherosclerotic plaque in one of the brain's main arteries that ahs broken off and gotten stuck "downstream." TIA are also caused by blood clots that originate in the heart, travel to the brain, and become lodged in a small artery there.

By definition, the symptoms of a TIA last less than 24 hours, in contrast to the symptoms of a stroke, which last longer--and are often permanent. Common TIA symptoms include sudden weakness in an arm or leg on one side of the body, dimness or loss of vision in one eye, dizziness (usually with other symptoms), and difficulty speaking or understanding what other people are saying.

Doctors used to think that the arterial blockages of TIAs didn't last long enough to cause permanent brain damage. But we know now that it's not...

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