Concussion Linked to Risk for Dementia, Parkinson's, ADHD

Erik Greb

August 11, 2020

Concussion is associated with increased risk for subsequent development of attention-deficit/hyperactivity disorder (ADHD), as well as dementia and Parkinson's disease, new research suggests.

Results from a retrospective, population-based cohort study showed that controlling for socioeconomic status and overall health did not significantly affect this association.

The link between concussion and risk for ADHD and for mood and anxiety disorder was stronger in the female participants than in the men. In addition, having a history of multiple concussions strengthened the association between concussion and subsequent mood and anxiety disorder, dementia, and Parkinson's disease compared with experiencing just one concussion.

Dr Marc Morissette

The findings are similar to those of previous studies, noted lead author Marc P. Morissette, PhD, research assistant at the Pan Am Clinic Foundation in Winnipeg, Manitoba, Canada.

"The main methodological differences separating our study from previous studies in this area is a focus on concussion-specific injuries identified from medical records and the potential for study participants to have up to 25 years of follow-up data," Morissette told Medscape Medical News.

The findings were published online July 27 in Family Medicine and Community Health, a BMJ journal.

Almost 190,000 Participants

Several studies have shown associations between head injury and increased risk for ADHD, depression, anxiety, Alzheimer's disease, and Parkinson's disease. However, many of these studies relied on self-reported medical history, included all forms of traumatic brain injury, and failed to adjust for preexisting health conditions.

An improved understanding of concussion and the risks associated with it could help physicians manage their patients' long-term needs, the investigators note.

In the current study, the researchers examined anonymized administrative health data collected between 1990–1991 and 2014–2015 in the Manitoba Population Research Data Repository at the Manitoba Center for Health Policy.

Eligible patients been diagnosed with concussion in accordance with standard criteria. Participants were excluded if they had been diagnosed with dementia or Parkinson's disease before the incident concussion during the study period. The investigators matched three control participants to each included patient on the basis of age, sex, and location.

Study outcome was time from index date (date of first concussion) to diagnosis of ADHD, mood and anxiety disorder, dementia, or Parkinson's disease. The researchers controlled for socioeconomic status using Socioeconomic Factor Index, version 2 (SEFI2), and for preexisting medical conditions using the Charlson Comorbidity Index (CCI).

The study included 28,021 men (mean age, 25 years) and 19,462 women (mean age, 30 years) in the concussion group and 81,871 men (mean age, 25 years) and 57,159 women (mean age, 30 years) in the control group. Mean SEFI2 score was approximately −0.05, and mean CCI score was approximately 0.2.

Dose Effect?

Results showed that concussion was associated with an increased risk for ADHD (hazard ratio [HR], 1.39), mood and anxiety disorder (HR, 1.72), dementia (HR, 1.72), and Parkinson's disease (HR, 1.57).

After experiencing a concussion, the risk of developing ADHD was 28% higher and the risk of developing mood and anxiety disorder was 7% higher among women than men. Gender was not associated with risk for dementia or Parkinson's disease after concussion.

Sustaining a second concussion increased the strength of the association with risk for dementia compared with sustaining a single concussion (HR, 1.62).

Similarly, sustaining more than three concussions increased the strength of the association with the risk for mood and anxiety disorders (HR for more than three vs one concussion, 1.22) and Parkinson's disease (HR, 3.27).

A sensitivity analysis found similar associations between concussion and risk for mood and anxiety disorder among all age groups. Younger participants were at greater risk for ADHD, however, and older participants were at greater risk for dementia and Parkinson's disease.

Increased awareness of concussion and the outcomes of interest, along with improved diagnostic tools, may have influenced the study's findings, Morissette noted.

"The sex-based differences may be due to either pathophysiological differences in response to concussive injuries or potentially a difference in willingness to seek medical care or share symptoms, concussion-related or otherwise, with a medical professional," he said.

"We are hopeful that our findings will encourage practitioners to be cognizant of various conditions that may present in individuals who have previously experienced a concussion," Morissette added. "If physicians are aware of the various associations identified following a concussion, it may lead to more thorough clinical examination at initial presentation, along with more dedicated care throughout the patient's life."

Association vs Causation

Commenting for Medscape Medical News, Steven Erickson, MD, sports medicine specialist at Banner – University Medicine Neuroscience Institute, Phoenix, Arizona, noted that although the study showed an association between concussion and subsequent diagnosis of ADHD, anxiety, and Parkinson's disease, "this association should not be misconstrued as causation."

He added that the study's conclusions "are just as likely to be due to labeling theory" or a self-fulfilling prophecy.

"Patients diagnosed with ADHD, anxiety, or Parkinson's disease may recall concussion and associate the two diagnoses; but patients who have not previously been diagnosed with a concussion cannot draw that conclusion," said Erickson, who was not involved with the research.

Citing the apparent gender difference in the strength of the association between concussion and the outcomes of interest, Erickson noted that women are more likely to report symptoms in general "and therefore are more likely to be diagnosed with ADHD and anxiety disorders" because of differences in reporting rather than incidence of disease.

"Further research needs to be done to definitively determine a causal relationship between concussion and any psychiatric or neurologic diagnosis," Erickson concluded.

The study was funded by the Pan Am Clinic Foundation. Morissette and Erickson have disclosed no relevant financial relationships.

Fam Med Community Health. Published online July 27, 2020. Abstract

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