Dubbed the "Iron Lady," Britain's hard-nosed former Prime Minister Margaret Thatcher was revered for her nimble command of world events and her quick verbal repartee.
But today, in a soon-to-be-published memoir, her daughter Carol describes an 82-year-old woman -- the world leader once feared and admired -- as humbled by memory lapses so severe she doesn't even know that her longtime husband has died.
Readers across Britain called the publication of details of Thatcher's decline "exploitive" and "opportunistic." But reaction to the memoir also underscores the shame many feel about the consequences of dementia especially when it strikes the most intellectually powerful.
"It's obviously a tragedy," said Ronald Reagan Jr., whose political father suffered for many years from the most common form of dementia -- Alzheimer's disease -- before his death in 2004. "But the idea of going into details of [Thatcher's] dementia are in monumentally bad taste and unnecessary."
"I suspect there is still a vestige of that in the disease's nature," Reagan told ABCNews.com. "It affects the brain and becomes a mental illness in a way."
Dementia -- a Latin word for "irrationality" -- is an umbrella term for more than 100 diseases that affect the brain in old age, according to the National Institutes for Health. An estimated 2 million to 4 million Americans have some form of the disease.
Perhaps the most highly publicized case was that of former President Reagan -- Thatcher's conservative political soul mate. He went public with his diagnosis in a televised statement in 1994, a decade before he died of the disease.
Goldwater, Heston Also Sufferers
Other powerful figures who suffered from dementia were Hollywood icon and Reagan friend Charlton Heston, as well as 1964 Republican presidential contender Barry Goldwater and professional boxer Sugar Ray Robinson.
"Ronnie's long journey has finally taken him to a distant place where I can no longer reach him," said Reagan's wife, Nancy, just a month before he died in 2004. "Because of this I'm determined to do whatever I can to save other families from this pain."
In the case of Thatcher, she suffered several mild strokes before doctors advised her against public speaking in 2002. In March she was admitted to a hospital for tests after she felt ill during a House of Lords dinner.
Serving as prime minister from 1979 to 1990, she had been an intellectual powerhouse, reportedly sleeping just four hours a night. Her daughter Carol Thatcher, a television personality, said she first noticed her mother's memory problems in 2000.
In her memoir, "A Swim-On Part in the Goldfish Bowl," which will be published next month, her daughter describes Thatcher's inability to remember world affairs or even the 2003 death of her husband, Denis.
"I had to keep giving her the bad news over and over again," the younger Thatcher writes. "Every time it finally sank in that she had lost her husband of more than 50 years, she'd look at me sadly and say 'Oh' as I struggled to compose myself. 'Were we all there?' she'd ask softly."
Most people remain "alert and able" as they age, but after age 65, the risk for dementia rises quickly, according to the NIH. Two percent of all Americans suffer from dementia before the age of 69, but by age 80, the risk increases to 20 percent. At 90, one-third of all people have some form of dementia.
Many health experts say dementia is more common today because of longer life expectancies. About two-third of its victims are women, probably because they live longer.
Some of the common symptoms include asking the same questions repeatedly; becoming lost in familiar places; being unable to follow directions; getting disoriented about time, people and places; and neglecting personal safety, hygiene and nutrition.
Changes in personality and behavior can also be signals, particularly if it affects work or daily activities.
Two of the most common forms of dementia in older people are Alzheimer's and multi-infarct or vascular dementia. In the latter, a series of strokes or changes in the brain's blood supply may cause death of brain tissue and symptoms usually develop abruptly.
An estimated 60 percent to 70 percent of all dementia patients have Alzheimer's, which tends to develop as a slow progression, according to Neil Buckholtz, chief of dementias of the Aging Branch at the National Institute on Aging.
Thatcher likely has Alzheimer's disease because of the slow progression of her memory lapses, according to Buckholtz, who has not treated the former prime minister. Oftentimes, "pure" dementia and that disease can overlap and one exacerbates the other.
Alzheimer's disease can take as long as 20 years to develop, which led some to speculate that Reagan, who left office in 1988 and was diagnosed in 1994, could have had early signs of the disease in office.
"President Reagan was physically active and that may have contributed to a longer [development] time for him," said Buckholtz. Other behaviors that can slow the disease are staying engaged mentally and socially.
There is nothing to suggest that Thatcher, too, had early disease while in office, according to Buckholtz.
Confused Falkland Islands With Bosnia
Her daughter first noticed symptoms during a lunch in 2000. The once razor-sharp Thatcher confused Bosnia with the Falkland Islands during a conversation about the former Yugoslavia.
"I almost fell off my chair," writes Carol Thatcher. "Watching her struggle with her words and her memory, I couldn't believe it. She was in her 75th year but I had always thought of her as ageless, timeless and 100 percent cast-iron damage-proof. From the fateful day of our lunch, tell-tale signs that something wasn't quite right began to emerge."
Doctors can never be completely sure whether the memory-related symptoms are Alzheimer's disease or another form of dementia, though an MRI test can give some clues. Only an autopsy provides the "pathological gold standard," said Buckholtz.
"Because prominent people do have Alzheimer's, it may be a surprise, but it shouldn't be," he told ABCNews.com "Although there is some indication that people with more education and higher education levels are at a reduced risk."
While some dementias are reversible, Alzheimer's is not and modern drugs only slow its progression.
"You lose your sense of self and it's very difficult on family members and caregivers who see a person who doesn't recognize them anymore," he said.
Meanwhile, the details of Thatcher's disease are being doled out in Britain's The Mail.
The author, Thatcher's now 55-year-old daughter -- a twin, whom the British tabloids portrayed as jealous of her more flamboyant and doted upon brother -- appears to have written her own "Mommy Dearest."
"On bad days, she could hardly remember the beginning of a sentence by the time she got to the end," she writes. "I had to learn to be patient, a quality I admit is in short supply. I also had to learn she had an illness and that it wasn't personal. That's the worst thing about dementia: It gets you every time."
Reagan's youngest son offered his condolences on Thatcher's now-public condition and agreed the insidious disease can strike anyone, regardless of their mental acumen.
"The disease doesn't respect your mental faculties any more than any other disease, like cancer or the flu," said Reagan, now a political commentator for MSNBC.
Still, Reagan, whose family only painted a positive face of the once-hearty former president, was critical of Carol Thatcher.
"What exactly does the public learn when we hear she doesn't recognize her family?" he asked. "Everyone knows what it does and what happens: You forget names, places, things. To detail that is shameful."
"People should think about how they would feel if it were their mother," Reagan said of the intimate details of Thatcher's mental decline. "The word is 'salacious.'"
Amanda Platell of Britain's Daily Mail, which is serializing the memoir, agreed.
"It felt not only like a terrible invasion of an old woman's privacy, but a personal betrayal," she wrote. "There's a time and place for such memoirs. But this was not it. Too soon, Carol. Too much detail."