Sports-related concussion has received increasing attention as a cause of short- and long-term neurologic symptoms among athletes. The King-Devick K-D test is based on measurement of the speed of rapid number naming reading aloud single-digit numbers from 3 test cards , and captures impairment of eye movements, attention, language, and other correlates of suboptimal brain function. We investigated the K-D test as a potential rapid sideline screening for concussion in a cohort of boxers and mixed martial arts fighters. The K-D test was administered prefight and postfight.
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Although the King-Devick K-D test has been used frequently in assessing sports related concussion early after injury, its characteristics over time after injury and in patients with prolonged persistent symptoms are unknown. The purpose of this paper was to: evaluate the ability of the K-D Test to distinguish patients seen early after concussion from those with symptoms persisting more than 3 months compared to controls, assess changes in the K-D test times over time after concussion, and determine the relationship of K-D times to the Stroop Color and Word Test scores.
We performed cross-sectional comparisons of patients with recent concussive brain injury acute group and those with symptoms persisting more than 3 months to healthy controls on the K-D test, the Sports Concussion Assessment Tool 3 SCAT3 , and the Stroop Color and Word Test. Longitudinal comparisons of the acute group over time within the first month after injury were also made.
K-D times at the second visit for the acute group were similar to those of controls While SCAT3 scores improved over time in the acute group, the K-D scores did not change between the first and second visit K-D scores correlated significantly with the Stroop scores for all three participant groups. The K-D test is likely useful very early after concussion in conjunction with baseline scores, and while scores in PCS patients remain elevated, they can be confounded by factors such as pre-morbid depression and medication use.
High correlations with Stroop scores also suggest that performance on the K-D test can by proxy provide additional insight about cognitive function and predict performance on more cognitively demanding tasks. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability: Due to ethical restrictions imposed by the St.
Michael's Hospital Research Ethics Committee, the data underlying this study are available to interested, qualified researchers upon request to: Dr. The funders had no role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing interests: The authors have declared that no competing interests exist. Rising public concern regarding the occurrence of mild traumatic brain injuries mTBIs including concussion in sports has led to the development of tools that can help assist in the screening, diagnosis and follow-up of these injuries.
Symptoms on the SCAT3 can be counted and given a rating of severity, but these scores share the same limitations of all self-reported scales: they may be difficult to assess in the presence of preexisting symptoms and are open to potential bias as athletes may under or over-report their symptoms. Due to such limitations, other tests have been investigated that can help aid clinicians in the screening and diagnosis of those suspected of brain injury.
The K-D test requires that participants read a series of three test cards of numbers, which become progressively more difficult to read, as quickly as they can [ 2 ]. The total time to complete all three test cards, and the number of errors committed are included in the total score. Studies have shown the K-D test to be a sensitive marker of brain injury by detecting attentional deficits and impaired saccadic eye movements, which have been associated with higher worse K-D scores among athletes [ 3 — 6 ].
The K-D test has become a popular sideline screening tool for concussions in sports, since it is easy to administer and usually takes less than two minutes to complete. Several studies have used it in hockey league cohorts [ 7 — 9 ], boxing and mixed martial arts MMA competitions [ 10 , 11 ], football games [ 6 , 12 — 15 ], as well as rugby league competitions [ 5 , 15 — 18 ]. Despite its extensive use immediately following a suspected TBI, the efficacy of the K-D test in tracking symptom resolution longitudinally has been less widely investigated.
Tjarks et al. They found that K-D scores improved at each visit over the four-visit study period [ 19 ]. In addition, only Silverberg [ 20 ] and Benedict et al. To our knowledge, previous studies have also not explored the option of correlating performance on the K-D test with tests assessing executive functions such as inhibitory control to see if the K-D test can by-proxy provide more understanding into cognitive function after head injuries.
The purpose of this study was three-fold. First, we wanted to determine if the K-D test could accurately distinguish between non-injured healthy controls, acutely injured patients, and those with persistent post-concussive syndrome with symptoms lasting more than 3 months PCS. We hypothesized that higher worse K-D test scores would be seen in the acutely injured group and PCS patients compared to healthy controls.
Second, we aimed to determine if K-D test scores changed over time from the original injury among the acute group patients and if it correlated to symptom resolution over time. We hypothesized that K-D scores would correlate with self-report symptom scores and show improvement over time as symptoms resolved.
Our third aim was to correlate and compare K-D scores with assessments of selective attention and processing speed, namely the Stroop Color and Word Test. Our hypothesis was that scores of the Stroop assessment would negatively correlate with K-D scores.
Healthy controls were recruited through word of mouth to family members or relatives of participants, as well as staff at SMH in the Emergency Department. Participants must have been able to: communicate, understand their current medical condition, understand the purpose of the research study, understand the option of declining to participate with no impact on medical care , understand the risks of participating, and make a decision that is not substantially based upon hallucinations, delusions, or cognitive signs of depression.
If any of these criteria were not met, we did not proceed to consent. Acute group patients were defined as patients who had suffered a non-penetrating head injury and exhibited a GCS score of 13—15 at the time of recruitment. PCS patients were defined as those who had sustained a mTBI three or more months prior to their first testing visit, and were still experiencing ongoing symptoms.
Inclusion criteria included: being the age of 16 or over, being able to provide informed written consent, and having sufficient fluency in English. Controls participants must also not have had a history of prior head injuries. All participants were also asked to complete a screening form to ensure their eligibility.
In addition, participants were excluded if they were unable to provide consent because of being medically unstable or intoxicated at the time of recruitment. At the time of screening we also asked for current medication use. PCS participants and controls were asked to come in for one visit, and those in the acute injury group were asked to come in for two visits.
PCS and healthy controls were asked to come in at their earliest possible convenience. The first visit for acute participants was conducted within 10 days of the injury, while the second was conducted at 2—4 weeks post-injury PI.
The minimum time between the first and second visit was seven days. The descriptions of these tests are outlined below. The K-D test is a saccadic eye measurement test that relies on the principle of rapid number naming [ 1 — 15 ].
The test contains a demonstration practice card and three test cards of variably spaced single-digit numbers [ 1 — 3 , 5 ]. Participants are asked to read out aloud the numbers from left to right as quick as they can without making any errors [ 1 — 15 ]. The time taken for each card as well as the number of errors was recorded and summed to provide the total K-D score [ 1 — 15 ].
The test usually takes less than two minutes to complete [ 3 , 5 ]. The symptom evaluation is composed of 22 different symptoms, each of which are rated on a scale of 0—6, with 0 indicating absence of symptoms and 6 being most severe [ 17 , 21 ]. The total score is out of 22, with symptoms being counted towards the total score if they are non-zero values [ 17 , 21 ].
The symptom severity score is obtained by summing the values of the individual symptom scores, resulting in a maximum score of [ 17 , 21 ]. The Stroop Color and Word Test is a neuropsychological test used to measure executive control and selective attention [ 22 — 25 ]. Participants are asked to name the colour of the words presented as fast as they can [ 22 — 25 ].
This becomes more difficult to do if the colour is incongruent with the word [ 23 — 25 ]. The scores on the task reflect how well participants can selectively direct attention to task relevant features while ignoring task-irrelevant features [ 23 — 25 ]. In our study, participants were asked to read the colour of words blue, red, green on a sheet of paper as fast as they can. There were 10 rows, each containing 10 words, resulting in a total of words.
The time limit was 45 seconds. If participants finished early, they were asked to read again from the beginning.
The total number of words and number of errors are included in the final score. Descriptive statistics were used to describe the participants. Paired t-tests were used to do compare scores between the first and second visit for the acute group. Pearson correlation coefficients were used to calculate the correlation between the test scores. All analysis was conducted using Stata The demographic data pertaining to each participant group are outlined in Table 1. Of these 12 participants in the PCS group, 3 were using benzodiazepines, 6 were using antidepressants, and 5 were using medications ibuprofen, acetyl salicylic acid, acetaminophen to relieve headaches.
For the first visit, K-D mean scores were K-D scores were not different from the first to second visit in the acute group For the acute group, symptom scores and severity scores improved significantly from the first visit to the second We also performed an analysis of K-D values over time to show the pattern of scores in the acute group. A scatterplot Fig 1 showing K-D scores and the time between date of injury and test visits showed no significant correlation or relationship.
Again, there were no significant differences between each time interval in terms of K-D scores. Abbreviations: SD, standard deviation. For the Stroop Color and Word Test, the acute group at the first visit got fewer words correct than the controls A strong, inverse correlation was found for all three groups Table 3.
We found that PCS patients performed significantly worse than controls and moderately worse than our acute group of patients on the K-D test. A number of potential explanations exist for this. Our PCS patients sustained their injuries more frequently in motor vehicle crashes MVC than the acute group and since MVC injuries are higher velocity events than those in sports, they are likely also linked with increased concussion severity and the prolongation of symptom burden [ 26 — 31 ].
Those suffering from PCS may have experienced greater damage to cortical and subcortical structures in the prefrontal cortex, thus resulting in ongoing cerebral impairment and slowing of saccades beyond the usual month period in which most decrements in cognitive function resolve [ 26 , 32 ]. In addition, the PCS group was more medicated for conditions like depression or anxiety which can contribute to prolongation of K-D times and post-concussive symptoms. Reilly [ 33 ] found that the usage of benzodiazepines and other sedatives used to relieve anxiety have been associated with a decrease in saccadic acceleration and velocity and an increase in saccadic latency, or the time interval between two consecutive saccades, which would slow down saccadic eye movements [ 33 ].
However, it was also reported that the usage of antidepressants had no significant effect on saccadic eye movements [ 33 ]. So, it is difficult to be certain whether tests of saccadic eye movements can be used as sensitive and objective markers of brain dysfunction following injury, particularly in patients on confounding medications for depression or anxiety [ 33 ].
As we only conducted one test session for PCS participants, we were not able to determine at what point in time K-D scores worsened. A study by Heitger [ 26 ] showed saccadic eye movements among PCS patients to be significantly worse at days PI compared with those with good recovery. Rizzo [ 32 ] also examined performance on the K-D test and found significant differences between PCS and healthy controls at a median of 54 weeks PI.
It is plausible that differences scores on the K-D test might already arise by days PI and remain elevated past the 1 year mark. To our knowledge, no studies have so far administered the K-D test over multiple test visits in a span of multiple months to over a year PI. Future studies should focus on conducting more frequent visits over time, to better elucidate the pattern of performance on saccadic eye movement tests such as the K-D test among those suffering from chronic concussion.
In terms of symptom scores, we found higher symptom and symptom severity scores among the PCS group compared to both controls and the acute mTBI, suggesting prolongation of symptom burden in this group. A strong possibility is that symptoms related to PCS might not stem from concussion per se but are also influenced by psychological, personality, and psychosocial factors. Individuals react differently to injuries, and it is plausible that those suffering from PCS may develop a shaken sense of identity as concussion recovery takes longer than usual.
This may lead to cognitive issues by suppressing attention, mental efficiency, learning and memory, therefore creating symptoms that are unrelated to those caused by the concussion itself [ 34 ].
The King-Devick test as a determinant of head trauma and concussion in boxers and MMA fighters
Although the King-Devick K-D test has been used frequently in assessing sports related concussion early after injury, its characteristics over time after injury and in patients with prolonged persistent symptoms are unknown. The purpose of this paper was to: evaluate the ability of the K-D Test to distinguish patients seen early after concussion from those with symptoms persisting more than 3 months compared to controls, assess changes in the K-D test times over time after concussion, and determine the relationship of K-D times to the Stroop Color and Word Test scores. We performed cross-sectional comparisons of patients with recent concussive brain injury acute group and those with symptoms persisting more than 3 months to healthy controls on the K-D test, the Sports Concussion Assessment Tool 3 SCAT3 , and the Stroop Color and Word Test. Longitudinal comparisons of the acute group over time within the first month after injury were also made. K-D times at the second visit for the acute group were similar to those of controls
King Devick Test
Quickly recognize impaired eye movements on the sidelines with King-Devick Test in association with Mayo Clinic. The King-Devick Test is a two-minute rapid number naming assessment in which an in individual quickly reads aloud single digit numbers and evaluates impairments of eye movements, attention and language function Concussion, The King-Devick test of rapid number naming for concussion detection: meta-analysis and systematic review of the literature, Peer-reviewed research has shown that adding a vision-based performance measure to cognitive and balance testing enhances the detection capabilities of current sideline concussion assessment Journal of Neuro-Ophthalmology, Adding Vision to Concussion Testing: A Prospective Study of Sideline Testing in Youth and Collegiate Athletes Any worsening of King-Devick Test from baseline indicated a five-times greater likelihood of concussion Concussion, The King-Devick test of rapid number naming for concussion detection: meta-analysis and systematic review of the literature, Some off-label uses of devices described in the peer-reviewed scientific research have not been cleared by FDA.