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, Dr. 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,” Dr. 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 versus causation
Commenting on the research, Steven Erickson, MD , sports medicine specialist at Banner–University Medicine Neuroscience Institute, Phoenix, Ariz., 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 Dr. 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, Dr. 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,” Dr. Erickson concluded.
The study was funded by the Pan Am Clinic Foundation. Dr. Morissette and Dr. Erickson have disclosed no relevant financial relationships.
A version of this article originally appeared on Medscape.com.