Epidemiology of progressive multifocal leukoencephalopathy in Japan and effectiveness of mefloquine: A retrospective analysis of a nationwide inpatient database

Progressive multifocal leukoencephalopathy (PML) is an infrequent yet devastating neurological infection that arises in immunocompromised patients. The epidemiological features of PML in Japan and its evolution in recent years remain unclear. There are no established treatments that directly target PML. Although mefloquine has shown in vitro activity against JC virus, its clinical effectiveness has not been confirmed in population-level studies. We retrospectively analyzed the admission data of patients with PML recorded in the Diagnosis Procedure Combination (DPC) database from fiscal year 2010 to 2020 (11 years). Descriptive statistics were used to illustrate the epidemiological features. Changes in the frequency of PML admission, underlying diseases, and in-hospital mortality over time were also examined. Furthermore, we evaluated the effectiveness of mefloquine in improving activities of daily living at discharge using propensity score matching. We identified 610 PML cases diagnosed by the treating physicians, which may include possible PML. Among them, 419 were first-time admissions. The median age at admission was 62.0 years, and 62.8% were men. HIV was the most common underlying condition, accounting for 22.9% of cases, followed by hematologic malignancies (18.4%), and autoimmune diseases (17.9%). Over the study period, the frequency of PML admissions showed an increasing trend, whereas the in-hospital mortality rate showed a decreasing trend. The effectiveness of mefloquine was not confirmed. The results of this study will help clarify and update the clinical picture of PML in Japan. The DPC database was shown to be useful tool for epidemiological research on rare infectious disease such as PML. •The Progressive Multifocal Leukoencephalopathy epidemiology in Japan was described.•HIV was the most common underlying condition, accounting for 22.9% of the cases.•HIV was followed by hematological malignancies and autoimmune diseases.•Related admissions increased and in-hospital mortality decreased over study period.•The effectiveness of mefloquine could not be confirmed.