November 14, 2018
The twofold increased suicide risk revealed by the meta-analysis, which included 700,000 individuals with head trauma and more than 6 million individuals with no such history, came as a "surprise" to investigators.
"We were surprised to see just how many studies had identified that concussion was a clear risk factor for suicide, suicide attempt, and suicidal thoughts," principal investigator Michael Fralick, MD, of the Departments of Medicine and Epidemiology, University of Toronto, Canada, told Medscape Medical News.
However, he cautioned, the absolute number of suicides in the study was low.
"The take-home message is that over 99% of people who have a concussion will not have a suicide-related outcome," he added.
The study was published online November 12 in JAMA Neurology.
Largest Analysis to Date
In 80% of individuals with concussion, neurologic symptoms resolve within 7 days of injury. However, the investigators note that up to 25% of patients experience chronic neuropsychiatric symptoms &mdash including anxiety and depression — that may persist years after the initial injury.
"Although there has been anecdotal evidence reported in newspaper reports, movies, and documentaries suggesting a link between concussion and/or mild TBI and subsequent suicide, past studies on the topic have been limited by small sample sizes and conflicting results," the investigators write.
To assess suicide risk after concussion, the investigators conducted a systematic review and meta-analysis that included 713,706 patients who had been diagnosed with concussion and 6,236,010 individuals who had no history of concussion or mild TBI.
"Our team chose this [research] method after we learned there were a few large studies that investigated the association between concussion and suicide. By first identifying all past studies on the topic and then combining their results, it provides the largest and most update summary of the available studies of concussion and suicide," said Fralick.
The researchers identified 17 relevant studies published from 1963 to May 2017. These included 10 cohort studies, five cross-sectional studies, and two case-control reports. The review also included unpublished reports presented at annual conferences of the American Academy of Neurology from 2012 to 2017.
The studies were conducted in North America, Scandinavia, and Australia. Seven reports included military personnel, and three studies primarily focused on children or students.
Suicide Is Rare
In individuals who had been diagnosed with concussion or mild TBI, the investigators found a 2.03 relative risk (RR) for suicide (95% confidence interval [CI], 1.47 - 2.80) compared to the unaffected comparison population (P < .001).
The RR increased slightly when the meta-analysis was restricted to studies that adjusted for factors associated with concussion and/or mild TBI and suicide (RR = 2.10; 95% CI, 1.40 - 3.13). This finding also was statistically significant (P < .01).
The absolute risk of suicide varied from 0.28% to 0.59%
"We observed a higher risk of suicide for people diagnosed with concussion and/or mild TBI compared with those without such diagnoses. Despite this heightened risk, nearly all patients diagnosed with concussion and/or mild TBI did not die by suicide," the researchers note.
Studies that assessed suicidal ideation or suicide attempt were heterogeneous in design and were not included in the analysis.
"However, most of these studies reported a heightened risk of suicide attempt or suicidal ideation for people diagnosed with mild TBI compared with those not diagnosed," the researchers note.
The odds ratios for suicidal ideation ranged from 1.12 to 2.60. For studies that included data on suicide attempts, odds ratios ranged from 0.65 to 19.1.
Interestingly, military personnel who had a history of concussion or mild TBI did not have a higher risk for suicide. The combined estimate for military populations (RR, 1.46; 95% CI, 0.80 - 2.58) was lower than the estimated risk among nonmilitary participants (RR, 2.36; 95% CI, 1.64 - 3.40). This finding was also significant (P < .01).
Fralick speculated that the reason military personnel had a lower relative risk for suicide may be "because there were few studies of military personnel. Certainly future work in this area is necessary to better understand what we observed."
To Screen or Not to Screen
The results raise the question as to whether screening for suicidal ideation or behaviors is warranted.
"Studies have not identified whether screening for suicide risk is helpful after someone has had a concussion," Fralick said. "Anecdotally, I do ask my patients about symptoms of depression and/or suicidal thoughts if they have had a concussion."
In terms of limitations, most studies only provided relative risks in terms of rate ratios or odds ratios, the researchers note.
"Therefore, we could not conduct a meta-analysis to quantify the absolute number of excess cases of suicide attributable to concussions and/or mild TBIs," they write.
Another potential limitation is that studies that included absolute risk varied considerably with respect to follow-up times. In addition, few studies included the risk for suicide among athletes and children, "populations that may be at greatest risk of concussion and adverse sequelae," the investigators write.
There is hope for higher-quality data going forward. An ongoing prospective registry in the United States will include a broad range of patients with concussion and mild TBI. However, findings from this registry are at least a decade away, the investigators note.
Whether certain characteristics make some individuals more susceptible to these risks after concussion and/or mild TBI remains unknown.
"Future research is needed so we can identify this subgroup of people and develop strategies to reduce their risk of suicide-related outcomes," Fralick said.
In an accompanying editorial, Donald A. Redelmeier, MD, and Junaid A. Bhatti, MBBS, PhD, of the Departments of Medicine and Surgery at the University of Toronto, contend that "neurologists need to be aware of the suicide risks and consider screening patients with a concussion for additional factors, including substance use, mood disorders and past suicide attempts.
"Psychiatrists should also consider a concussion history when judging an individual patient's suicide risk. We should all recognize that a concussion, in its own way, can be lethal," the editorialists add.
Redelmeier and Bhatti note that the study's strongest contribution is in "providing a comprehensive review of medical science that suggests a significant association between concussions and an increased risk of subsequent suicide."
A weakness of this specific meta-analysis is that correlation does not prove causality, they note.
"Patients who receive a diagnosis of a concussion might have already had a latent psychiatric illness that contributed to the incident and the outcome. However, an overly skeptical interpretation is unjustified because a concussion could also amplify a latent psychiatric illness," they write.
The study findings warrant future studies to evaluate the molecular mechanisms that connect concussions to subsequent cognitive dysfunction, they conclude.
Dr Fralick, Dr Redelmeier, and Dr Bhatti have disclosed no relevant financial relationships.