Attention-deficit/hyperactivity disorder (ADHD) affects approximately 11% of children in the United States, and some previous research has suggested that that exposure to stimulants commonly used to treat the disorder (such as amphetamine or methylphenidate) can result in persistent basal ganglia dopaminergic deficits. Now, new research shows that patients with ADHD have an increased risk of developing Parkinson disease (PD) and related basal ganglia and cerebellum (BGC) diseases, and patients treated with stimulants have an even greater risk.
In a paper published today in Neuropsychopharmacology, researchers from the University of Utah explain that patients with ADHD were more than twice as likely to develop early-onset PD or a BGC disease than peers who do not have ADHD. Among patients with more severe disease who are prescribed stimulant medications to control their ADHD, the risk was 6- to 8-fold higher.
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Using the Utah Population Database (which contains records of more than 11 million individuals, or 85% of patient encounters in Utah annually), the investigators in this retrospective cohort study, led by Glen Hanson, DDS, PhD, professor of pharmacology and toxicology in the school of dentistry at the University of Utah, examined records of patients who were at least 20 years old in 2011. They arrived at a cohort of 31,769 individuals with a history of ADHD, 4960 of whom were treated with stimulants. An age- and sex-matched cohort of 158,790 individuals with no ADHD history was randomly selected.
In the ADHD cohort, the rate of incident BGC diseases was 0.52%, compared with 0.19% in the non-ADHD cohort, and the age of disease onset was slightly younger (43 years) among patients with ADHD than in those without ADHD (45 years).
Overall, the adjusted hazard ratio (aHR) for BGC diseases in patients with ADHD was 2.4 (95% CI, 2.0-3.0; P < .0001), while in patients whose ADHD was treated with stimulants, the risk was significantly higher (aHR, 6.0; 95% CI, 3.9-9.1; P <.0001) than it was for those without stimulant treatment (aHR, 1.8; 95% CI, 1.4-2.3; P <.0001).
Among patients who had a BGC disease, 32.3% of patients without ADHD and 33.7% of patients with ADHD had PD. A 2.6-fold increased risk of PD was observed for the patients with ADHD versus those without ADHD (95%CI 1.8-3.7; P <.0001).
The study’s authors cautioned that, while patients whose treatment for ADHD included stimulants had a higher risk of BGC diseases in general and PD in particular, the observed risk may not be directly linked to stimulants .
“The jury is still out,” said Karen Curtin, PhD, associate professor of internal medicine at the University of Utah, and one of the authors of the paper, in a statement. “The increased risk we observed in people could be linked to having ADHD itself or perhaps a more severe form of ADHD, which may be more likely to be treated with medications.”
Hanson did encourage patients to discontinue treatment for ADHD, saying, “I believe the treatment is still a benefit, especially for children who cannot control their ADHD symptoms,” Hanson said. “Medication really should be considered on a case-by-case basis.”
Curtin K, Fleckenstein AE, Keeshin BR, et al. Increased risk of diseases of the basal ganglia and cerebellum in patients with a history of attention-deficit/hyperactivity disorder [published online September 12, 2018.] Neuropsychopharmacology. Accessed September 12, 2018.