In-hospital outcomes and documented 90-day readmission to the index hospital in older patients with Parkinson's disease hospitalised for lower respiratory tract infection: a single-centre retrospective cohort study.

Background: Lower respiratory tract infection (LRTI) is a major cause of hospitalisation in older adults with Parkinson's disease (PD), but it remains uncertain whether PD-related measures provide clinically relevant information beyond general vulnerability and acute infection severity. Methods: We conducted a single-centre retrospective cohort study of patients aged ≥65 years with neurologist-diagnosed PD who were hospitalised for LRTI between 2018 and 2025. The primary outcome was a composite of intensive care unit admission, invasive mechanical ventilation, or in-hospital death. Documented readmission to the index hospital within 90 days among survivors was analysed as a secondary exploratory outcome. Multivariable logistic and Cox regression models evaluated clinical factors associated with these outcomes. A hierarchical extension added Hoehn-Yahr stage and pre-admission wheelchair- or bed-bound status to the base clinical model. Calendar-period analyses and bootstrap internal validation were performed. Results: Among 246 patients, 62 (25.2%) experienced the composite in-hospital outcome. In the PD-specific extended model, higher Charlson Comorbidity Index (adjusted odds ratio [OR] per 1-point increase 1.19, 95% confidence interval [CI] 1.00-1.42), hypoxaemia (OR 2.00, 95% CI 1.01-3.96), serum albumin <35 g/L (OR 3.18, 95% CI 1.65-6.14), sepsis or septic shock (OR 2.41, 95% CI 1.17-4.98), and pre-admission wheelchair- or bed-bound status (OR 2.08, 95% CI 1.08-4.01) were associated with the outcome. Hoehn-Yahr stage, PD duration, tube feeding, and antiparkinsonian medication burden were not independently associated. Among 228 patients discharged alive, 74 (32.5%) had a documented readmission to the index hospital. Hypoalbuminaemia (adjusted hazard ratio [HR] 1.82, 95% CI 1.12-2.95) and non-home discharge (HR 1.96, 95% CI 1.19-3.24) were among the factors associated with documented same-hospital return. Bootstrap-corrected discrimination was 0.81 for the extended logistic model and 0.70 for the Cox model. Conclusion: Severe in-hospital deterioration was associated mainly with general physiological vulnerability, acute infection severity, and pre-admission mobility dependence, whereas most other available PD-specific measures showed no clear independent association. These findings support integrated clinical assessment but not a validated PD-specific prediction strategy; the post-discharge analysis reflects documented return to the index hospital rather than complete population-level readmission.