Association between Proteinuria and Risk of Chronic Inflammatory Demyelinating Polyneuropathy/Multifocal Motor Neuropathy: A Nationwide Population-based Cohort Study

BACKGROUND: This study aimed to determine whether proteinuria is associated with the subsequent development of chronic inflammatory demyelinating polyneuropathy (CIDP) and multifocal motor neuropathy (MMN). METHODS: We conducted a population-based retrospective cohort study using the Korean National Health Insurance Service database. Individuals aged ≥ 20 years who underwent national health screening in 2009 (N = 3,937,902) were followed until December 2020. Participants with a prior history of CIDP/MMN or diagnosis within one year of screening were excluded. Proteinuria was assessed via urine dipstick (positive ≥ 1+). The primary outcome was incident CIDP/MMN, defined by the concurrent presence of ICD-10 code G61.8 and Rare and Intractable Disease program code V126. Cox proportional hazards models examined the association, adjusting for potential confounders. RESULTS: At baseline, 2.5% of individuals had proteinuria. During follow-up, 210 individuals developed CIDP/MMN. The incidence rate was significantly higher in those with proteinuria (1.44 per 100,000 person-years) than in those without (0.50 per 100,000 person-years). After adjustment for demographics, lifestyle, and comorbidities, proteinuria remained significantly associated with increased CIDP/MMN risk (adjusted hazard ratio 2.32; 95% confidence interval 1.35-4.03). This association was consistent across subgroups defined by sex, age, and chronic kidney disease. CONCLUSION: Proteinuria is associated with a modest risk of developing CIDP/MMN. These findings suggest possible shared immunopathologic mechanisms involving antigens or immune pathways common to both the kidney and peripheral nerves. Neurologic monitoring may be warranted in individuals with proteinuria.