Older adults diagnosed with autism face a significantly higher risk of developing movement disorders related to Parkinson’s disease than the general population, according to a large study published in the journal Autism.

Researchers analyzed Medicare and Medicaid claims involving nearly 57 million Americans aged 45 and older. The data covered the period from 2017 through 2019.

Adults on the autism spectrum, as well as people with intellectual disabilities, received parkinsonism diagnoses at substantially higher rates than people without autism.

Parkinsonism describes a range of neurological conditions involving movement symptoms. According to the Parkinson’s Foundation, those symptoms can include tremors, muscle rigidity, balance problems and slowed voluntary movement.

Earlier research had suggested an overlap between autism and motor decline later in life. However, researchers had not determined whether those problems stemmed from the condition or from antipsychotic medications known to cause symptoms resembling Parkinson’s.

To examine whether medication use explained the association, researchers excluded people who took antipsychotic medications. Higher rates of diagnoses related to Parkinson’s remained among the neurodivergent populations.

In the general population control group, the prevalence of parkinsonism was approximately 1.57%. It rose to 3.83% among adults with autism alone and 4.32% among those with an intellectual disability alone.

The highest prevalence, 4.86%, appeared among people diagnosed with both autism and an intellectual disability.

“A critically important new contribution of this study is increased incidence rates of parkinsonism for autistic people in middle and older adulthood, which suggests that these cases aren’t simply a byproduct of lifelong motor challenges,” Greg Wallace said in a press release.

Wallace is the lead author and a professor in the Department of Speech, Language and Hearing Sciences at The George Washington University in Washington, D.C.

The study marked the first time scientists tracked the incidence rate, meaning the risk of newly emerging cases over time, among older autistic people.

“It is therefore important for clinicians to establish clear baselines of motor skills and challenges during adulthood that can be tracked over time,” Wallace added.

Dr. Lee Murray, a neurologist based in Jackson, Tennessee, said the findings clarify previous research indicating that patients with autism face a higher risk of having Parkinson’s. Murray was not involved in the study.

“This study takes into account the use of antipsychotic medications that can cause a Parkinson's look (resting tremor, stiffness, shuffled gait, stooped posture, softened voice), which is a different pathology than stereotypical or idiopathic Parkinson's disease,” Murray told Fox News Digital.

“This study showed patients with autism that was associated with intellectual disability seem to have the greatest association with concomitant Parkinson's.”

Murray cautioned that autism includes a broad range of symptoms and levels of severity. The findings do not mean people with milder cases necessarily face a significantly higher risk of Parkinson’s disease.

“It certainly is an interesting correlation, although it does not imply that someone with autism is certain to develop Parkinson's,” Murray added.

“From a clinical perspective, it's helpful to review medications with the autistic patient's physicians and, if possible, try to avoid medications that may cause a Parkinson's appearance.”

The study’s authors identified several limitations related to their use of Medicare and Medicaid insurance records. Billing and diagnostic codes can contain errors or reflect differences in how clinics and medical providers diagnose conditions.

Claims data also prevented the researchers from evaluating the severity of individual motor symptoms. They could not examine the possible roles of lifestyle factors, genetics or family history.

The records included only adults enrolled in public insurance programs. That limitation may have excluded older adults who rely exclusively on private health insurance.

Diagnosis can also be complicated because autistic people may experience coordination problems, repetitive behaviors or executive functioning challenges. Early signs of Parkinson’s disease could therefore be missed or mistaken, potentially delaying care.

“Patients with autism can have atypical movements that can be misdiagnosed as Parkinson's if the examiner is not accustomed to diagnosing it,” Murray said.

Researchers emphasized that physicians, long term care facilities and family caregivers should closely monitor older autistic patients for declining motor function. Such monitoring could allow interventions to begin as early as possible.