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. Post-concussive syndrome (PCS) patients had significantly higher K-D times compared to controls (p = 0.01), while the acute group did not differ from controls (p = 0.33). K-D times at the second visit for the acute group were similar to those of controls (54.7 vs. 49.6, p = 0.31). While SCAT3 scores improved over time in the acute group, the K-D scores did not change between the first and second visit (55.2 vs. 54.7, p = 0.94). 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.
Summary Points:
- 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.
- PCS patients performed significantly worse than controls and moderately worse than the acute group of patients on the K-D test.
- Results did not show positive correlation between K-D scores and symptom scores suggesting that the reporting of subjective symptoms does not predict performance on K-D Test.
- Given results in the acute group tested within 10 days of injury the findings do not support the acute mTBI screening use of the K-D Test without a baseline score.
- Results showed novel and robust finding that K-D times were significantly correlated with Stroop Color and Word Test (patients with better, faster K-D Test times had more words correct in the Stroop Color and Word Test supporting the use of the K-D Test to indirectly indicate the level of interference control and selective attention measured by the Stroop Color and Word Test. This provides convergent validity for the K-D Test as it also assesses mental abilities such as selective attention.
- The K-D Test can by-proxy provide insightful information about more complex cerebral functions associated with selective attention, such as response inhibition.
Findings support the value of the K-D Test as a screening test very early after injury.