Most people dismiss simple things like forgetting their keys as a part of getting older. But it can be a symptom of mild cognitive impairment (MCI), a level of cognitive functioning often characterized by forgetfulness and difficulty performing tasks that used to be easy.

Mild cognitive impairment is a possible early sign of Alzheimer's disease. Two new studies, led by researchers at the University of Southern California, found that most people with MCI are unaware they have it, and most primary care physicians underdiagnose it.

One reason a mild cognitive impairment is underdiagnosed is that it is not highly symptomatic. People get used to living with MCI and adapt to it.

MCI is very common in the older population, Soeren Mattke, an author on both studies, told TheDoctor. But without a diagnosis, patients cannot take preventive measures or take advantage of new treatments for Alzheimer's disease that can slow cognitive decline.

The brain is limited in its ability to recover from cognitive impairment because brain cells do not grow back, so damage can no longer be repaired. For that reason, Mattke explained, “For MCI caused by Alzheimer's disease, the earlier you treat it, the better your outcomes.”

The first study, published in Alzheimer's Research & Therapy, analyzed data from more than 40 million Medicare beneficiaries 65 years old and older.

Fewer than eight percent of expected cases of mild cognitive impairment were actually diagnosed when they compared the proportion of those diagnosed with MCI to the proportion expected to be diagnosed for this age group. That amounts to more than seven million undiagnosed cases among the eight million projected cases of MCI.

“We thought the numbers would be bad, but we didn't really expect them to be that bad,” said Mattke, director of the Brain Health Observatory at the Center for Economic and Social Research at USC.

People with conditions such as cardiovascular disease, diabetes and hypertension are at higher risk for MCI. These conditions are more common among communities of color, putting them at increased risk for MCI. Yet in the first study, the detection rate of MCI among Black Medicare beneficiaries was almost four percent and for Latinx beneficiaries almost five percent. For Non-Hispanic white beneficiaries, the detection rate was almost 10 percent.

These statistics are concerning because although the incidence of MCI is higher in these populations, the detection rate is lower, Mattke explained. “So they are hit twice. They have a higher risk of MCI, yet lower detection rates.”

The second study, published in the Journal of the Prevention of Alzheimer's Disease, was an analysis of data from more than 220,000 primary care clinicians. It found that 99 percent of the doctors underdiagnosed MCI. It takes about 15 minutes to diagnose MCI, said Mattke. One reason MCI may go undiagnosed is that time must be set aside during a clinical visit to discuss changes in cognitive functioning. This discussion usually does not happen, unless the the appointment was scheduled specifically for this purpose.

Another reason MCI is underdiagnosed is that it is not highly symptomatic. People get used to living with MCI and adapt to it. Said Mattie, “They think it is just normal.”

Patients may not ask for an evaluation because they are afraid of being told they have MCI. In some states, a physician has to report a dementia diagnosis to the state health department or the department of motor vehicles. Reporting this diagnosis could result in patients losing their driver's licenses. “So there are practical and psychological reasons to not mention symptoms,” Matttke said.

The hope, going forward, he added, is to see what can be done to increase the detection rate among primary care patients, so “We could give primary care providers better tools to identify MCI and increase rates of diagnosis.”