OBJECTIVES:

Mild cognitive impairment (MCI) is the transitional stage between normal cognitive aging and dementia. In 2021, the US Food and Drug Administration approved the use of aducanumab for the treatment of Alzheimer's disease (AD). Collecting data on MCI-to-AD progression would be useful for future evaluations of its effectiveness. This study aimed to characterize the progression of new MCI cases in Japan using claims data.

METHODS:

The analysis was conducted using a medical and long-term care claims database produced by the LIFE Study. Five-year data (2015 to 2019) from National Health Insurance and Latter-Stage Elderly Healthcare System enrollees residing in 12 Japanese municipalities were analyzed. New MCI cases were defined as those without any previous MCI diagnosis in the past 6 months. Post-MCI progression was analyzed using (1) the incidence of MCI-to-AD progression among new MCI cases who could be followed-up for 36 months and (2) Kaplan-Meier curves to estimate MCI-to-AD progression among new MCI cases. Subjects were identified as those with a recorded diagnosis of MCI (ICD-10: F067) and AD (G30).

RESULTS:

We identified 638 new MCI cases with 36 months of follow-up data. Among these, 93 cases (14.6%) simultaneously received AD and MCI diagnoses. There were 105 AD cases (16.5%) in the first year, 23 cases (3.6%) in the second year, and 2 cases (0.3%) in the third year; 336 cases (52.7%) did not develop AD during the follow-up period. However, 79 cases (12.4%) had received AD diagnoses before the MCI diagnosis. The Kaplan-Meier curves showed that the cumulative incidence of MCI-to-AD progression was 27.3% in the 12th month, 36.6% in the 24th month, and 41.8% in the 36th month.

CONCLUSIONS:

Characterizing the AD progression of MCI cases in Japan provides important fundamental data for subsequent effectiveness evaluations and budget impact analyses of aducanumab after it is approved for the Japanese market.