John and Teresa Kerry. (Michael Dwyer / AP)

Teresa Heinz Kerry moved to a rehabilitation hospital Thursday as her condition continued to improve, a spokesman said Thursday.

A rep for John Kerry said that doctors have concluded that the secretary of state’s wife suffered a seizure on Sunday. They still don’t know what caused it, though possibilities such as a tumor or stroke have been ruled out.

With her condition upgraded from “fair” to “good,” the 74-year-old ketchup heiress was moved from Boston’s Massachusetts General Hospital to nearby Spaulding Rehabilitation Hospital, Kerry spokesman Glen Johnson said.

Kerry has left his wife’s side only briefly this week, attending the opening of a high-level summit with Chinese officials in Washington Wednesday before returning to Boston. A tentatively planned trip to the Middle East, where he’d hoped to bring Israel and the Palestinians back to the negotiating table, has not been scheduled.

Earlier: Teresa Heinz Kerry ‘doing better,’ says a teary John Kerry, 7/10/13
Teresa Heinz Kerry: Condition improves, possible causes ruled out, 7/9/13
Teresa Heinz Kerry: The quiet presence behind the secretary of state, 7/8/13

More Reliable Source: Timothy Geithner; Jay-Z; royal baby name; Randy Travis; Justin Bieber; Ray Allen; Sam KassKastles opener