Barbara Bush underwent radiation therapy two years ago and is still on medication from her bout with an out-of-kilter thyroid.

Like her husband's newly diagnosed hyperthyroidism, Mrs. Bush's problem was caused by the production of excess amounts of hormones from the thyroid gland.In the first lady's case, the specific thyroid problem was diagnosed as Grave's Disease, which caused her to experience double-vision and a sudden loss of weight.

The White House called the first lady's thyroid specialist in to help deal with President Bush's case after blood tests pointed to the thyroid as the cause of the irregular heartbeat that forced his hospitalization last weekend.

The specialist is Dr. Kenneth Burman, an Army colonel and endocrinologist at Walter Reed Army Medical Center in Washington.

Mrs. Bush, 65, underwent 10 radiation treatments after being diagnosed with Grave's Disease in March 1989.