More than half of people who likely have dementia don't know it, according to a new study from Johns Hopkins Medicine.  They are either undiagnosed or unaware of their diagnosis.

The study, published in the July issue of the Journal of General Internal Medicine, adds to evidence that dementia, which affects an estimated 5.5 million people in the United States, is underdiagnosed and underdisclosed. It suggests that family members may want to take a more active role in the medical appointments of older adults.

While there are no good treatments for dementia, Halima Amjad, a geriatrician who was lead author of the study, said not knowing about cognitive decline has safety implications for patients and their families. People with dementia will need to stop driving at some point.  It may not be safe for them to cook.  They may run into trouble managing their money or medications.  They may not be able to live alone.

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Unlike other diseases, she said, dementia can affect the "entire life and entire health of the patient."

The Alzheimer's Association on Sunday released recommended practice guidelines for doctors and nurses that are meant to improve diagnosis of dementia and patient care.  The guidelines call for assessments of all middle-aged and older people who are aware of cognitive changes themselves or whose care partners or clinicians have noticed changes. A family member or confidant should "almost always" be involved in the evaluation, the association said.

Amjad's study was based on analysis of information from the National Health and Aging Trends Study, which provided information about probable dementia, and from Medicare claims data, which provided actual diagnoses.  The research team found that 58.7 percent of the 585 older adults with probable dementia included in the study were either undiagnosed or unaware of their diagnosis.  Only 41 percent knew they had been diagnosed with dementia. About 40 percent of the group was undiagnosed.  The rest had a diagnosis but didn't know it.  It is possible they had been told but did not remember.

Coming to physician appointments alone and having relatively few impairments were risk factors both for not knowing about a diagnosis and for being undiagnosed.  Patients with probable dementia who were Hispanic or had less than a high school education were less likely to have had a diagnosis.

Amjad said professional organizations currently don't recommend universal screening for dementia. Medicare recommends it during a patient's annual wellness visit, but the screening can be as simple as asking a patient if he's noticed any problems.  She thinks targeting at-risk populations for more attention could be helpful.

An equally important step may be educating family members about early signs of dementia and how it progresses.  Some people, she said, think forgetfulness is a normal part of aging.  Older patients should also be encouraged to bring a family member or close friend with them to appointments.  "I think a lot of patients might be open to doing that if it's mentioned that it's important," she said.  Another option is to ask patients for the phone number of someone who knows them well that the doctor can call.  "Most patients are open to you talking to other people.  It's just a matter of asking," Amjad said.  This is helpful when the patient might not remember to bring someone to the next visit.

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Some patients may resist giving someone else access to such private information.  If they do, Amjad said, doctors can at least try to connect them with community resources, including experts who can assess whether they need more support.

Jason Karlawish, co-director of the Penn Memory Center, said specialists in dementia care recognize the value of "knowledgeable informants."  If a patient says he doesn't have one, that's a red flag.  "It should raise your index of concern that there may be things going on in this person's daily life that could be harmful," he said.  That includes financial exploitation and medication mix-ups.

Most people have seen a primary care doctor before they come to someone like Karlawish.  He urges those doctors to ask patients with cognitive complaints to bring someone to the next appointment with them, and put the request in writing.  An added challenge is that having another person attend appointments may increase the time and space needed, if the doctor wants a private conversation with the companion.

Carol Lippa, director of the Cognitive Disorders and Comprehensive Alzheimer's Disease Center at Jefferson University Hospitals, said it is well-known that people with less education are more vulnerable to dementia because they have less cognitive reserve.  This group also can be harder to evaluate, especially if their baseline functioning was low.

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Like Amjad, she thinks friends and family members can play an important role.  "Dementia is hard to diagnose without someone with a good memory to convey any problems with daily functions," she said.  People with dementia may also have trouble making an appointment for testing, and navigating the health system by themselves.

Confused patients often forget to bring a friend or relative to their follow-up visit, she said.  But they also often carry cell phones, and that can make it easier for the practitioner to contact friends or relatives. "If patients carry a phone, they are usually fine having me call to confirm their functional status," Lippa said. "In fact, most are appreciative."