A national Medicare case-crossover study found that extreme heat modestly increases the odds of hospitalization with Parkinson’s disease (small but significant cumulative OR ~1.02 for 99th vs 50th percentile over 3 days), with stronger effects in temperate regions.

This epidemiologic evidence highlights a climate- and region-specific risk factor relevant for clinical guidance and public-health planning for PD patients, but it offers limited mechanistic or therapeutic discovery insight.

BACKGROUND: The projected rise in U.S. Parkinson's Disease (PD) cases makes understanding risk factors crucial to plan for changing healthcare utilization patterns. Factors such as extreme heat exacerbated by shifts in regional climate conditions may present additional risks among the PD population. OBJECTIVE: We aim to determine whether nationwide and climate region-specific acute heat index exposure is associated with increased rates of hospitalizations with PD among the Medicare population. METHODS: We follow a time-stratified case-crossover study design for a population of Medicare fee-for-service beneficiaries within the contiguous U.S. hospitalized between 1 January 2000 and 31 December 2016. The exposure of interest is the daily maximum heat index during the warm season (May-September), converted to percentiles using climate region-specific warm season heat index distributions. We used distributed lag models to estimate the immediate and lagged associations of heat index on hospitalization with PD. RESULTS: Our sample included 427,813 individuals (89.3% White, 47.7% female, mean age 79.8). In nationwide analyses, the odds ratio (OR) of hospitalization with PD comparing days in the 99th versus 50th percentile of the heat index distribution was 1.010 (95% CI 1.002, 1.017). Results suggest extreme heat effects persist 2 days beyond the initial day. The cumulative OR of hospitalization with PD after 3 days of continuous exposure (i.e., cumulative over lags 0-2) to heat indexes at the 99th versus 50th percentile was 1.022 (95% CI: 1.005, 1.039). Estimates were larger in temperate climates, while tropical, arid, and continental regions showed varying impacts with non-significant associations. SIGNIFICANCE: High heat index exposure is associated with increased odds of hospitalization with PD amongst older adults, particularly those living in temperate climates in the US South. These results may inform both medical practice and policy through crafting PD-patient-centered hotweather advice and via the issuance of local and state extreme heat advisories. IMPACT: For an aging society, the threat of increased frequency of extreme heat from climate change poses significant risks to older adults, especially those living with Parkinson's Disease (PD). Our work addresses gaps in several preceding studies by exploring more fully how effects of extreme heat on the risk of PD-related hospitalization differ across climate types and by sex. The additional insight presented in our analysis can equip practitioners and policymakers with the data required to help mitigate the threats of extreme heat on patients with PD.