Abstract Background Diagnosing early-onset Alzheimer’s disease (EOAD) has unique challenges compared with late-onset AD (LOAD), but the diagnostic journey in Japan is unknown. The objectives of this study were to evaluate the time from symptom onset to diagnosis of EOAD compared with LOAD in Japan, and to investigate factors affecting the time to diagnosis. Methods Patients aged between 18 and 79 years who were diagnosed between April 2011 and March 2023 at participating facilities across Japan with “probable AD dementia”, “mild cognitive impairment due to AD”, or an equivalent diagnosis were included. Patients were categorized by age of onset as EOAD (< 65 years) or LOAD (≥ 65 years). Eligible EOAD and time-matched LOAD patients were enrolled. This retrospective observational study was registered in the UMIN Clinical Trials Registry on 28 November 2023 (UMIN000052928). Results The mean (standard deviation) time from symptom onset to diagnosis (primary endpoint) was 138.3 (91.0) weeks for EOAD ( n = 79) and 99.6 (81.5) weeks for LOAD ( n = 59) ( p = 0.011). Time from symptom onset to first medical visit was 89.0 (74.2) weeks (EOAD) and 57.6 (71.5) weeks (LOAD) ( p = 0.024). No difference between EOAD and LOAD was found in the time after the first medical visit to diagnosis. Conclusions In Japan, patients with EOAD experienced a longer time to diagnosis than patients with LOAD. Symptoms, regional differences, and access to medical care may have influenced the time to diagnosis. Therefore, it is important to raise awareness of the disease and the need for early consultation, even among non-elderly individuals. Trial registration UMIN000052928.
Kasuga et al. (Thu,) studied this question.