Summary: People living with a neurological or mental health condition face a higher risk of developing a second, related disorder later in life. For example, individuals with Parkinson’s disease were found to have about four times the rate of developing dementia; those with psychiatric disorders also showed an elevated risk of later dementia.
Source: University of Waterloo
New population-based research shows that many common neurological and psychiatric disorders are linked, often bidirectionally, and that sex influences the likelihood of developing a second condition.
Researchers from the University of Waterloo and the Institute for Clinical Evaluative Sciences analyzed more than a decade of provincial health records to map associations between widely occurring brain and mental health conditions. Supported by the Neurodegenerative Disease Research Initiative (ONDRI) through the Ontario Brain Institute, this study is the largest of its kind in Ontario in both scale and duration.
“Neurological and psychiatric disorders are among the leading causes of disability and death worldwide,” said Colleen Maxwell, a professor at the School of Pharmacy at the University of Waterloo and lead author on the study. “Identifying which conditions increase the risk of others, and how long that risk persists, can help clinicians, caregivers and health systems intervene earlier and plan better care.”
The team examined linked health administrative data for more than five million Ontario residents aged 40 to 85, following diagnoses over 14 years. They focused on common, high-burden conditions such as dementia, Parkinson’s disease, stroke and mood or anxiety disorders, and assessed how having one disorder affected the likelihood of developing another. Importantly, the researchers evaluated these links in both directions—for example, how prior stroke affected later dementia risk and how prior dementia affected later stroke risk.
In nearly all pairings examined, a prior diagnosis of one condition was associated with a higher rate of developing a second condition. Notable findings included a roughly fourfold increase in the rate of dementia among people with prior Parkinson’s disease and more than a twofold increase in dementia risk after stroke. Prior psychiatric disorders were also associated with an elevated rate of subsequent dementia. For some condition pairs, an increased risk remained evident for a decade or more after the first diagnosis.
The analysis also revealed meaningful sex differences in absolute risk. For example, women who had experienced a stroke were more likely than men with stroke to develop dementia later on. Overall, many associations were strongest within the six months following an initial diagnosis and followed a J-shaped pattern over time—showing elevated risk shortly after the first event, declining, and then in some cases rising again later.
Key numeric findings reported in the study include adjusted hazard ratios demonstrating increased rates of second conditions: dementia rates were higher after prior Parkinson’s disease (adjusted hazard ratio, adjHR, 4.05), after prior stroke (adjHR 2.49), and after psychiatric disorder (adjHR 1.79). Parkinson’s disease rates were higher after dementia (adjHR 2.23) and after psychiatric disorder (adjHR 1.77). Stroke incidence was elevated following dementia (adjHR 1.56). Prior dementia, Parkinson’s disease and stroke were each associated with higher rates of incident psychiatric disorders as well.
These patterns of bidirectional association suggest opportunities to improve early detection and coordinated care. Clinicians can use this information to monitor patients proactively for likely comorbid conditions, and health systems can plan resources and education to better address the overlap between neurological and psychiatric illness.
“Our findings can inform clinical practice, caregiver support and health-system planning,” Maxwell said. “They also point to the need for training programs that prepare health-care providers to recognize and manage common comorbidities across neurology and mental health.”
Funding: This research was supported by the Neurodegenerative Disease Research Initiative (ONDRI) through the Ontario Brain Institute.
About this neurology and mental health research news
Author: Ryon Jones
Source: University of Waterloo
Contact: Ryon Jones – University of Waterloo
Image: The image is in the public domain
Original Research: Closed access. “Incidence of neurological and psychiatric comorbidity over time: a population-based cohort study in Ontario, Canada” by Colleen Maxwell et al., published in Age and Aging.
Abstract
Incidence of neurological and psychiatric comorbidity over time: a population-based cohort study in Ontario, Canada
Introduction
Comprehensive, population-based studies that examine how common neurological and psychiatric disorders overlap and evolve over time are uncommon. Understanding the timing and strength of these associations can highlight windows for early diagnosis and intervention.
Methods
This retrospective cohort study used linked administrative health data for Ontarians aged 40–85 years as of 1 April 2002. The researchers estimated adjusted rates of incident dementia, Parkinson’s disease, stroke and mood/anxiety disorders over 14 years according to the presence and timing of a prior disorder, and evaluated sex differences in cumulative incidence.
Results
The cohort included 5,283,546 Ontarians (mean age 56.2 ± 12.1 years, 52% female). Compared with people without those prior conditions, the rate of incident dementia was substantially higher among those with prior Parkinson’s disease (adjHR 4.05, 95% CI 3.99–4.11), prior stroke (adjHR 2.49, 95% CI 2.47–2.52), and prior psychiatric disorder (adjHR 1.79, 95% CI 1.78–1.80). Parkinson’s disease incidence was higher after dementia (adjHR 2.23) and after psychiatric disorder (adjHR 1.77). Prior dementia, Parkinson’s disease and stroke were each associated with elevated rates of later psychiatric disorder. Associations were generally strongest within six months after the index diagnosis and showed a J-shaped pattern over time. Several conditions showed significant sex differences in absolute risk.
Conclusions
The observed bidirectional relationships between common neurological and psychiatric disorders highlight opportunities for earlier recognition and intervention, with potential to improve patient outcomes and better inform health-care planning.