A new study published in JAMA Neurology found that young-onset dementia—or dementia that occurs before the age of 65—may be more prevalent than previously believed, reports Judy George for MedPage Today.
In the study, the authors examined 95 studies published between January 1990 and March 2020 for a systematic review. Seventy-four of those studies—which together included 2,760,379 participants—were then included in a meta-analysis. The studies were primarily conducted in Europe and among older populations in Asia, North America, and Oceania.
Through the meta-analysis, the researchers estimated age-specific prevalence for dementia in five-year age intervals between the ages of 30 to 64. Results from each five-year age interval were then standardized using the World Health Organization (WHO) world standard population from 2000 to 2025, the U.S. standard population of 2000, and the European standard population from 2011 to 2020.
According to the researchers, the global age-standardized prevalence of young-onset dementia was 119 per 100,000 people, which corresponds to 3.9 million cases among people between the ages of 30 and 64 worldwide. Prevalence estimates ranged from 1.1 per 100,000 among people ages 30 to 34 to 77.4 per 100,000 among people ages 60 to 64.
According to the researchers, the global prevalence reported in the study is higher than two commonly referenced estimates, which were based on retrospective register-based studies. These previous studies showed a prevalence of 54 and 42.3 per 100,000 people.
Overall, the researchers found that highest-prevalence cause of young-onset dementia was Alzheimer's disease (41.1 per 100,000), followed by vascular dementia and frontotemporal dementia. However, prevalence for Alzheimer's disease was lower than the other two conditions until age 50.
The study also found that the age-standardized prevalence of young-onset dementia was 159.4 per 100,000 people in Europe—corresponding to around 500,000 cases—and 114.7 per 100,000 in the United States—corresponding to around 200,000 cases. The researchers said they attributed this difference primarily to differences in each population's ages, MedPage Today reports.
Findings likely 'an underestimation,' researchers say
The researchers said that while their findings indicated the prevalence of young-onset dementia "is higher than previously thought, it is probably an underestimation owing to lack of high-quality data."
The researchers cited several limitations of the study, including an underrepresentation of studies from Africa and low-income countries and the fact that 41 of the studies reported data only from patients ages 60 to 64. Additionally, some of the studies had small samples, and dementia diagnosis was not always defined or reported properly.
In an accompanying editorial, David Knopman, a physician at Mayo Clinic, wrote that dementia may be underdiagnosed at younger ages due to reliance on passive surveillance methods to identify cases. He wrote that using passive surveillance increases the odds of "undercounting or overcounting cases owing to misdiagnosis (e.g., young-onset dementia as a psychiatric disorder or vice versa) or of noncontact by the young patient with dementia with the medical system."
To improve the accuracy of future prevalence information, the study's authors recommended conducting more cohort studies and standardizing reporting procedures in prevalence studies.
Knopman also cited the "dramatic differences" between the prevalence and incidence of young-onset dementia and later-onset dementia. "Young-onset dementia is a particularly disheartening diagnosis because it affects individuals in their prime years, in the midst of their careers, and while raising families," he wrote. "Most dementia care is geared for older patients, and as a consequence, services are rarely available to address the needs of someone diagnosed with dementia in their 50s who has dependent children at home and a spouse who must continue working." (George, MedPage Today, 7/19)