Investigators at the University of Utah (U of U) Health have released some interesting, if not disturbing new findings: attention-deficit hyperactivity disorder (ADHD) patients have a greater risk of developing Parkinson's and Parkinson-like diseases than individuals with no ADHD history. The results from the new study were released in Neuropsychopharmacology through an article titled “Increased risk of diseases of the basal ganglia and cerebellum in patients with a history of attention-deficit/hyperactivity disorder.”

This new data is significant as 11% of children (4-17 years old) nationwide have been diagnosed with ADHD. Moreover, the long-term health effects of having ADHD and of common ADHD medications remains understudied.

“Parkinson's disease is commonly thought of as a neurodegenerative disease associated with aging,” explains senior study investigator Glen Hanson, D.D.S., Ph.D., professor of pharmacology and toxicology in the School of Dentistry at U of U Health. “This may be the first time where a childhood disease and its treatment may be linked to a geriatric expression of a neurodegenerative disorder.”

Employing a retrospective, population-based study, the research team found that ADHD patients were more than twice as likely to develop early onset (21-66 years old) Parkinson's and Parkinson-like diseases compared to non-ADHD individuals of the same gender and age. Amazingly, the estimated risk was six to eight times higher for ADHD patients prescribed stimulant medications, including methylphenidate (Ritalin, Concerta, Daytrana, Metadate, and Methylin), mixed amphetamine salts (Adderall), and dexmethylphenidate (Focalin).

“If we were to follow 100,000 adults over time, in one year we would expect 1 to 2 people will develop Parkinson's disease before age 50,” notes lead study investigator Karen Curtin, Ph.D., associate professor in internal medicine at U of U Health. “If we were to follow 100,000 adults prescribed treatment for ADHD over time, we estimate that over a year 8 to 9 patients will develop Parkinson's disease before age 50.”

However, the authors did caution that patients with a more severe type of ADHD may inherently be at an increased risk of motor neuron diseases like Parkinson's, and the results may or may not be a direct result of the stimulant medication. Future studies are needed to reach a more definitive conclusion.

“The jury is still out,” Dr. Curtin remarks. “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.”

The research team used the Utah Population Database (UPDB), which contains vital and medical records of more than 11 million individuals who have lived in the state, to examine twenty years of historical records. Eligible patients were born between 1950 to 1992, were at least 20-years old by the end of 2011, were residents of Utah after January 1, 1996, and had no prior diagnosis of Parkinson's or Parkinson-like diseases.

Using the UPDB, the U of U team compiled an ADHD population, consisting of 31769 patients, of which 4960 were prescribed stimulant medications (2716 received amphetamine salts, 1941 received methylphenidate, and 303 received both). The non-ADHD comparison population consisted of 158790 individuals who were matched to the ADHD group on gender and age (5 to 1).

In addition to accounting for differences in gender and age, the study controlled for the effects of psychotic disorders and tobacco use that could be associated with Parkinson's independent of ADHD. Patients with a history of drug or alcohol abuse were excluded from the study. The team was not able to account for other factors that could contribute to the development of Parkinson's disease, including head trauma, brain injuries, and environmental toxins.

According to Dr. Hanson, the study results should be considered preliminary. This study may be limited by the misclassification of non-ADHD subjects, who were diagnosed with the disorder outside of Utah, missed or incorrect diagnosis of Parkinson-like disease symptoms and the lack of information on the duration of use and dosage of ADHD medication prescribed.

“I believe the treatment is still a benefit, especially for children who cannot control their ADHD symptoms,” Dr. Hanson concludes. “Medication really should be considered on a case-by-case basis.”

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