Incidence and distribution of subtypes of early‐onset dementia in Japan: A nationwide analysis based on annual performance reports of the Medical Centers for Dementia

AIM Investigating the incidence rate of early-onset dementia is challenging. We explored the incidence rate of early-onset dementia in Japan using annual performance reports from the Medical Centers for Dementia. METHODS Medical Centers for Dementia are specialized health services for dementia established as part of Japan's national health program. There are 440 such centers nationwide as of 2018. Using the annual performance reports of these centers, we calculated the number of newly diagnosed cases of early-onset dementia or late-onset dementia from April 1, 2018 to March 31, 2019, and the composition ratio by diagnosis according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. The annual incidence rate of early-onset dementia was estimated using the number of cases as the numerator and the national population aged 18-64 years as the denominator. RESULTS In total, 1733 of cases were diagnosed with early-onset dementia, of which 52.1% were diagnosed as major neurocognitive disorder due to Alzheimer's disease, 8.9% major frontotemporal neurocognitive disorder, 8.8% major vascular neurocognitive disorder, 7.1% substance/medication-induced major neurocognitive disorder, 6.5% major neurocognitive disorder with Lewy bodies and 3.9% major neurocognitive disorder due to another medical condition. The annual incidence rate of early-onset dementia was estimated to be 2.47/100 000 person-years. CONCLUSIONS This study provides the first nationwide estimate of the incidence rate of early-onset dementia in Japan and suggests that Medical Centers for Dementia are important resources for the epidemiological monitoring of early-onset dementia nationwide. Geriatr Gerontol Int ••; ••: ••-•• Geriatr Gerontol Int 2020; ••: ••-••.