Parkinsonism Co-occurrence Among Older Autistic Adults, Adults With Intellectual Disability, and a Control Sample of Adults in National Health Care Claims Data

Emerging evidence suggests that Parkinson's Disease (PD)-related conditions (i.e., parkinsonism) co-occur more commonly with autism than in the general population. However, prior prevalence-based studies did not account for the influence of antipsychotic usage, which is linked to secondary parkinsonism as a possible side effect, or co-occurring intellectual disability (ID). In addition, no study of incidence rates of parkinsonism among older autistic adults has been completed to date. Prevalence and incidence were examined among 56,970,786 45+ year old persons across four groups (autism only, ID only, autism + ID, and control sample) utilizing U.S.-based, individually linked Medicaid and Medicare health care claims data from 2017 to 2019. Compared with the control sample (1.57%), highly elevated prevalence of co-occurring PD-related diagnoses was found across groups (autism only: 3.83%; ID only: 4.32%; autism + ID: 4.86%). This elevation in prevalence persisted after the exclusion of individuals prescribed antipsychotic medications. Whether examining broader or narrower (excluding secondary) parkinsonism, the age-standardized incidence or risk of newly documented co-occurring parkinsonism was highest in those with autism + ID, followed by those with autism only and those with ID only, all of which far outpaced control sample findings. Overall, elevated co-occurrence of autism and parkinsonism has significant scientific, clinical, and service-system implications.Lay AbstractSome studies find that people with autism are more likely to have co-occurring parkinsonism, or the core motor features linked to Parkinson's Disease, like tremors and slowed movements. However, previous prevalence (number of cases at any one point in time) studies usually did not account for the influence of antipsychotic usage, which is relatively high in autism and can be associated with parkinsonism symptoms. Prior studies also rarely examined the influence of intellectual disability (ID) on the co-occurrence of parkinsonism and autism. Finally, no study of incidence rates (i.e., newly emerging cases over time) of parkinsonism among older autistic adults has been completed to date. Prevalence and incidence of parkinsonism were examined among 56,970,786 45+ year old persons across four groups (autism only, ID only, autism + ID, and control sample) utilizing U.S.-based, individually-linked Medicaid and Medicare health care claims data from 2017 to 2019. Relative to the control sample (1.57%), highly elevated prevalence of co-occurring PD-related diagnoses was found across groups (autism only: 3.83%; ID only: 4.32%; autism + ID: 4.86%), even after the exclusion of individuals prescribed antipsychotic medications. Whether examining broader or narrower (excluding secondary) parkinsonism, the age-standardized incidence or risk of newly documented co-occurring parkinsonism was highest in those with autism + ID, followed by those with autism only and those with ID only, all of which far outpaced control sample findings. Overall, elevated co-occurrence of autism and parkinsonism has significant scientific, clinical, and service system implications.