Dementia causes impaired mental functions such as memory, speech and language. It affects reasoning, visual ability and personality.
Ross, who is with the Department of Veterans Affairs and University of Hawaii John A. Burns School of Medicine, said a national effort is needed to educate people to recognize early signs and seek treatment.
His findings, from research on 191 Japanese-American men with dementia in the Honolulu-Asia Aging Study, indicate the illness isn't detected in about 60 percent of cases. The results were published this week in the Journal of the American Medical Association's special edition on Alzheimer's disease. They were reported at an AMA news conference today in New York. Co-authors of Ross' paper were Robert D. Abbott, University of Virginia Division of Biostatistics; Drs. Helen Petrovitch, Kamal H. Masaki and J. David Curb, all with the UH School of Medicine; Carolyn Murdaugh, University of Arizona College of Nursing; Carol Trockman, Honolulu-Asia Aging study, Kuakini Medical Center, and Dr. Lon White, leader of the aging study, with the National Institute on Aging.
White calculated the cost of dementia in Hawaii at about $400 million annually. "Web's paper is the first ever to really measure the magnitude of how big the iceberg is underneath what's showing above the surface," White said.
In an interview, Ross said potentially 1.8 million people in the United States over age 65 have "unrecognized or silent dementia," based on his study. Yet early recognition and treatment could reverse memory decline from subdural hematomas, drug intoxication, vitamin B12 deficiency, hypothyroidism and central nervous system infections.
"It's vital to initiate treatment in the early stages to prevent functional impairment," he said. "There will never be a treatment to bring back brain cells that are dead. We have to catch them before they're affected."
Cognitive (memory) screening or a 20-minute mental status exam should be part of every physical examination for people over 65, Ross said.
Alzheimer's disease accounts for 60 percent to 80 percent of all dementia cases worldwide, he said.
About 30 percent to 40 percent of all cases involve vascular dementia, resulting from multiple strokes or one stroke in a part of the brain associated with memory, Ross said.
"It's astounding," he said, noting conservatively about 600,000 people with vascular dementia aren't receiving treatment. Appropriate medications can reduce or prevent risk factors for strokes causing dementia, he pointed out.
About 8 percent to 10 percent of cases are related to Parkinsonian disorders and under 5 percent to vitamin B deficiency, low thyroid, subdural hematomas or central nervous system infections, Ross said.
"Many physicians tend to accept some degree of memory problem as normal. Gradually, we are coming around to the idea that may not be the case, and there are ways to prevent it."
Ross said $80 billion to $100 billion is spent annually taking care of people with dementia in the United States. "If we can treat 30 percent, we can save millions."
The men identified with dementia in his study were all living at home on Oahu and had care givers or family members who could provide a competent family history, Ross said.
In more than 60 percent of the demented men, he said, memory problems weren't recognized or medically examined.
He said loss of memory often is associated with subtle things like sleep or medication. For older people, it's attributed to aging.
Cultural traditions may have been a factor in some cases, the study said, with some families denying memory failure out of respect for husbands or fathers, all first- and second-generation Japanese Americans.
Rather than memory loss, families tended to notice behavioral disturbances such as hallucinations, agitation and declining ability to dress or perform other daily activities, the research showed.
Highlights of the study of 191 Japanese-American men with dementia in the Honolulu-Asia Aging Study:
51 percent had a definite problem with thinking or memory, and 53 percent of that group -- or slightly more than one quarter of the entire group -- had received no medical evaluation.