Millions of Adults Have Undiagnosed Mild Cognitive Impairment

More than 9 in 10 people with mild cognitive impairment don’t realize they have this diagnosis, which can often be an early sign of Alzheimer’s disease, a new study suggests.

For the study, researchers examined data on about 40 million people ages 65 and older insured by Medicare, the U.S. health insurance program. Overall, only about 8 percent of the eight million cases of mild cognitive impairment (MCI) they expected to find in these health records were actually there. The rest — an estimated 7.4 million cases — were undiagnosed, according to study results published in The Journal of Prevention of Alzheimer's Disease.

“We expected MCI to be underdiagnosed but not by that much,” says lead study author Soeren Mattke, MD, DSc, a professor and director of the Center for Improving Chronic Illness Care at the University of Southern California in Los Angeles.

This is probably because symptoms like misplacing the car keys or forgetting an appointment can be mild and get dismissed as a normal part of aging, Dr. Mattke says. Beyond this, many clinicians may not prioritize diagnosing these cases, Mattke adds.

In fact, a separate study of 200,000 Medicare enrollees 65 and older treated at more than 54,000 primary care clinics found that 99 percent of doctors underdiagnosed MCI. This study, also coauthored by Mattke, found that just 8 percent of MCI cases get properly diagnosed.

“Formally diagnosing these cases takes time, which many clinicians don’t have, and the prevailing perception remains that diagnosing it is inconsequential,” Mattke says. “But with new approved treatments for Alzheimer’s disease, which causes around 50 percent of mild cognitive impairment cases, there is now a sense of urgency to find patients who benefit.”

Two new medicines, lecanemab and donanemab, have been shown in recently published clinical trials to slow the progression of Alzheimer’s disease, Mattke notes. These newer drugs work by reducing the accumulation of protein clumps in the brain known as amyloid-beta proteins that are thought to play a role in cognitive impairment. One challenge with these medicines, however, is that they carry a risk of serious side effects, including the potential for bleeding and swelling in the brain.

Lecanemab (Leqembi), won provisional approval from the U.S. Food and Drug Administration (FDA) in January and full clearance in July. Drugmaker Eli Lilly, said it expects an FDA decision on donanemab by the end of this year. Aducanumab (Adulhelm), another drug that targets amyloid, won FDA approval as an Alzheimer’s treatment in 2021, despite concerns in the medical community about the extent of its benefit for this condition.

Even though early diagnosis of mild cognitive impairment can help people take actions to improve brain function, there are a lot of questions about the necessity of treating patients with these newer drugs for Alzheimer’s disease, says Majid Fotuhi, MD, PhD, an adjunct professor and neurologist at George Washington University in Washinton, DC, who wasn’t involved in the new studies.

“While it is important for physicians to address cognitive decline in the elderly and help them identify the potential causes for such decline, it is also crucial that they do not rush to tell their patients they are one step away from developing Alzheimer’s disease and need to take anti-amyloid medications,” Dr. Fotuhi says.

People who do get diagnosed with mild cognitive impairment can often improve their symptoms and prognosis by addressing a variety of underlying health issues that can contribute to impaired brain function, Fotuhi adds. Among other things, people may see improved cognitive function when they get proper care for conditions that can contribute to the impairment, like type 2 diabetes, depression, insomnia, sleep apnea, dehydration, and a sedentary lifestyle.

“People who have been diagnosed with MCI need to have a detailed conversation with their physicians as to what factors may have contributed to their cognitive decline and to make sure all of the following conditions are fully addressed and treated,” Fotuhi says. “Treating these conditions will [improve] their cognitive function and delay the onset of dementia.”