United States President George H. W. Bush developed new atrial fibrillation and was diagnosed in 1991 with hyperthyroidism due to the disease and was treated at Walter Reed Army Medical Center with radioactive iodine. By coincidence (or so it is presumed, since the ultimate cause of this disease remains unknown), the president's wife, Barbara Bush, and the Bushes' pet dog, a springer spaniel named Millie, also developed the disease about the same time, which in Barbara's case produced severe infiltrative exophthalmos and a cosmetic change in the appearance of her eyes.