Co-morbidity burden in Parkinson’s disease: Comparison with controls and its influence on prognosis

BACKGROUND: Many aspects of co-morbidity burden in Parkinson’s disease (PD) are unclear, but it may be an important predictor of prognosis or confounder of associations in epidemiological studies. OBJECTIVES: To determine how best to assess co-morbidity burden in PD, to compare with matched controls, and investigate its association with prognostic outcomes. METHODS: Data from an incident, community-based cohort with prospective follow-up (the PINE study) were used (198 patients with PD and 151 controls). The reliability of three co-morbidity scales (the Charlson co-morbidity index (CCI), the Cumulative Illness Rating scale and a simple disease count) were evaluated. The association with mortality and development of dependency was assessed with Cox regression. The co-morbidity burden in PD and controls was compared at baseline and over 5 years of follow-up using linear mixed modelling. RESULTS: The CCI was more reliable and was an independent predictor of mortality with a time-dependent effect (hazard ratio = 1.27 [1.08–1.49] in first four years of follow-up; no significant association after four years). Associations between the other scales and mortality and between each scale and development of dependency were non-significant once adjusted for confounders. Co-morbidity burden was similar between cases and controls at baseline and there was no evidence of differential accrual of co-morbidity between patients and controls (p = 0.94). CONCLUSIONS: The CCI is probably the better scale for measuring co-morbidity burden in PD. There were no differences between PD and controls. Co-morbidity burden at diagnosis was associated with mortality in the early part of the disease course, but not later.