Association of Parkinsonism or Parkinson Disease with Polypharmacy in the Year Preceding Diagnosis: A Nested Case–Control Study in South Korea

Introduction: Published studies on the association between polypharmacy and parkinsonism or Parkinson disease are very limited. Objective: The objective of this study was to investigate whether polypharmacy is associated with parkinsonism or Parkinson disease in elderly patients. Methods: From a South Korean national health insurance sample cohort database for 2002–2013, we matched parkinsonism cases (defined by diagnosis codes for parkinsonism/Parkinson disease) and Parkinson disease cases (patients who had records for both Parkinson disease diagnosis and anti-Parkinson disease drug prescriptions) with controls. Logistic regression analysis evaluated the associations of parkinsonism/Parkinson disease with polypharmacy (i.e., five or more prescribed daily drugs) during the year preceding parkinsonism/Parkinson disease diagnosis, medications potentially associated with parkinsonism, and comorbidity status (using the Charlson Comorbidity Index score and hospitalization records). Results: The study population included 6209 cases and 24,836 controls for parkinsonism and 1331 cases and 5324 controls for Parkinson disease. In univariate logistic regression, odds ratios for parkinsonism/Parkinson disease increased significantly with increased polypharmacy, medications potentially associated with parkinsonism, Charlson Comorbidity Index score, or prior hospitalizations. In multiple logistic regression, odds ratios for parkinsonism/Parkinson disease (adjusted for medications potentially associated with parkinsonism and comorbidities) also increased with increased polypharmacy. Odds ratios (95% confidence interval) for Parkinson disease were higher than those for parkinsonism with stronger statistical significance: 1.41 (1.28–1.55) and 2.17 (1.84–2.57) for parkinsonism and 2.87 (2.30–3.58) and 4.75 (3.39–6.66) for Parkinson disease for between five and ten prescribed daily drugs and ten or more drugs, respectively. Conclusions: Polypharmacy in the year preceding diagnosis may be associated with an increased risk for parkinsonism/Parkinson disease. Medications potentially associated with parkinsonism were assumed to increase the risk for parkinsonism/Parkinson disease, but more studies are required to confirm this relationship.