Although no cognitive tests were administered to Reagan during his time in office (his doctors saw no need for them), he did begin receiving annual mental and psychological assessments in 1990, after undergoing surgery to remove a blood clot in his brain. The four-hour battery of tests, which would have detected signs of dementia, found nothing amiss for the first three years they were administered. "All parameters for his age absolutely were within the normal range," one of Reagan's doctors said. It was Reagan himself who announced the diagnosis of Alzheimer's in 1994.
There were certainly no indications of dementia (age, perhaps, but not dementia) when the 81-year-old former president delivered a 35-minute speech at the 1992 Republican National Convention, a performance Washington Post reporter Bob Woodward described as "flawless."
It must also be said that given that the average life expectancy of a patient diagnosed with Alzheimer's Disease is eight to 10 years, Reagan, who died in 2004 (10 years after his diagnosis), would have been extraordinarily long-lived for an Alzheimer's patient if he was already suffering from the disease, as some claim, in 1984.