Exclusion of older patients from randomized clinical trials in Parkinson's disease

Prevalence of Parkinson's disease (PD) increases with age. The purpose of this study was to evaluate the eligibility criteria in randomized clinical trials (RCTs) in PD, especially those limiting the enrollment of older adults. We examined RCTs of pharmacological and non-pharmacological anti-parkinsonian interventions registered with ClinicalTrials.gov and started from 2013 through 2022. Primary outcome was proportion of RCTs with an upper age limit of 85 years of age or less. Secondary outcome was proportion of RCTs with other exclusion criteria. Associations between trial characteristics and the presence of the age limits were determined using logistic regression. Our study included 420 RCTs. Two hundred thirty-nine (57%) of these had an upper age limit of 85 years of age or less. Proportion of these trials significantly increased over time. The odds of the presence of an upper age limit were significantly associated with the investigational site location, phase, and timeframe for the primary endpoint assessment. Three hundred fifty-six (85%) trials had other eligibility criteria limiting the enrollment of older patients; these often (n = 285; 68%) included cognitive impairment. Overall, 386 (92%) RCTs either explicitly excluded older adults or had criteria indirectly limiting their enrollment. Underrepresentation of older patients in clinical trials in PD considerably reduces the generalizability of their results. Some eligibility criteria should be modified to enable the investigators to assess the benefits and harms of new therapeutic interventions in older adults. This problem is important in view of rapidly growing number of older patients with PD.