To update the rurality index for Japan (RIJ) using the most recent national data and to test and evaluate the updated RIJ variants that incorporate alternative distance metrics and a modified classification of remote islands, thereby providing methodological guidance for their use in research and health policy.

Nationwide methodological study.

Japan.

All postal code areas in Japan; analyses were aggregated into municipalities and secondary medical care areas for evaluation.

Six RIJ variants (‘RIJ family’) constructed by combining three distance metrics (direct distance, road-based distance and travel time by car) and two island classifications (original RIJ and modified RIJ), standardised to a continuous 0–100 scale using percentile ranks.

Concordance among RIJ variants was assessed using Spearman’s rank correlation coefficients, quintile reclassification matrices and rank-difference analyses; convergent validity was evaluated using the national physician distribution index. Criterion-related validity was assessed using municipal-level life expectancy for men and women.

All RIJ variants had extremely high concordance (Spearman’s ≥0.99 across all pairwise comparisons). Compared with the previous RIJ classification, >98% of the geographic units remained in the same rurality quintile and

Despite differences in distance metrics and island classification, all RIJ variants captured highly similar underlying dimensions of rurality and demonstrated comparable validity. These findings indicate that rurality measurement in Japan is stable regardless of methodological refinements, allowing RIJ variants to be flexibly selected according to specific research or policy purposes without materially affecting conclusions.

The intestinal microbiota of people with Parkinson’s disease (PwP) differs significantly from that of healthy individuals. Given that altered microbiota may play a role in the pathogenesis of Parkinson’s disease, faecal microbiota transplantation (FMT) has been proposed as a potential therapeutic approach. However, the efficacy of FMT in improving motor symptoms in PwP has been inconclusive in some pilot randomised controlled trials (RCT). Previous RCTs on PwP employed simple FMT, but our modified approach—pretreatment with antibiotics before FMT (A-FMT)—has been shown to improve the engraftment rate of given species and the beneficial effects of FMT. This study aims to evaluate the efficacy and safety of A-FMT for PwP, particularly in those with motor fluctuations.

This study is a randomised, double-blind, placebo-controlled, parallel-group study with an 8-week observation period following a single A-FMT. Thirty clinically established PwP with prominent motor fluctuation episodes will be randomised 1:1 to FMT or placebo. Participants in both groups will receive antibiotic treatment prior to colonoscopy for FMT or placebo treatment. Primary and secondary endpoints will include subjective and objective evaluations of motor and non-motor symptoms and will be evaluated before and after antibiotic treatment and at 4 and 8 weeks after the procedure. Exploratory endpoints will include blood and faecal sample analyses, advanced brain MRI and pharmacokinetic assessment of levodopa concentrations during a levodopa challenge test.

This study has been approved by the ethical committee of Juntendo University in August 2024 (J24-005) and will be conducted in accordance with the Declaration of Helsinki, the Japan Ministry of Health, Labour and Welfare Clinical Trials Act and related laws and regulations. All patient data will be anonymised to protect privacy and used solely for study purposes. Results will be published in academic journals and presented at conferences.

jRCTs031240344.