New subtests included in the SCAT5 rapid neurological screen were normal in the majority of players undergoing off-field concussion screening. Sensitivity and specificity of the comprehension, passive neck movement, and diplopia subtests were 0, 8, 5% and 0, 91, 97%, respectively. The new neurological screen subtests did not affect the diagnostic accuracy of the SCAT5. No players had any abnormality in comprehension, or had diplopia, or painful passive neck movement, in the absence of abnormalities in other SCAT5 sub-components.
The SCAT5 is the fourth iteration of the Sports Concussion Assessment Tool [2]. The original version had a ‘neurological screening’ domain, including subtests similarly examining speech and eye motion [7]. However, these were subsequently removed from the SCAT2 and SCAT3 [8, 9], prior to re-introduction in the SCAT5 [2]. ‘Neck pain’ has been part of the symptom checklist in all SCAT editions, with a neck examination introduced from the SCAT3 onwards [9]. However, specific evaluation of full range of pain-free passive cervical spine movement is specific to the SCAT5.
Concussion is considered a subset of mild traumatic brain injury largely reflecting a functional disturbance of brain disturbance [1]. The new SCAT5 neurological subtests of comprehension and diplopia are blunt examinations, which might be expected to be normal in the absence of other grossly abnormal neurological symptoms or signs. The findings that these subtests were largely normal in a population without overt signs of concussion, and only abnormal in conjunction with other SCAT5 subtest abnormalities, may therefore be unsurprising. Previous studies have demonstrated visual problems associated with traumatic brain injury and more detailed neuro-ophthalmological testing might have utility in off-field concussion screening [10].
Pain on passive neck movement is not a traditional neurological examination, and neck pain would not be expected in an isolated functional brain injury. However, neck examination could provide useful information during concussion screening. Concussion is commonly associated with concomitant neck injury including muscle strain, ligamentous sprains or, rarely, arterial dissection or bony injuries, which could confound the detection of concussion [11]. Moreover, despite limited evidence, if the presence of a neck sprain is also predictive of concussion, passive neck movement could potentially be a useful screening test. However in this study, passive neck examination did not appear to add any value over and above other SCAT5 subtests.
The SCAT5 consist of multiple subtests applied concurrently. In this testing paradigm, as further subtests are added, sensitivity will increase and specificity fall. Ideally, to maximise diagnostic accuracy, the optimal combination of individual subtests would be chosen that individually demonstrate reasonable sensitivity to detect new cases of concussion over and above other subtests; but that also have satisfactory specificity to minimise false-positive cases. The performance of individual SCAT components for off-field concussion screening, and their optimal combination, has been examined previously [3]. In the current study, the new comprehension, passive neck movement, and diplopia subtests demonstrated worse performance than other individual SCAT subtests, with no additional value. Their very low sensitivities (0, 8, and 5%, respectively) also indicate that they could not be substituted for other SCAT5 components. These results should be generalizable throughout Rugby and, as the subtests tests are relatively simple, are likely to have external validity in other elite sports. It is essential to note that ‘the diagnosis of concussion relies on a clinical synthesis of complex, non-specific and at times contradictory information’ [2]. It has been shown previously that team doctors often use expert judgement when interpreting off-field screening tests results compared to baseline or normative thresholds [3]. Despite not providing direct information, it is therefore possible that the new neurological subtests provide global information to inform an overall clinical assessment. Importantly, the SCAT5 is also used in other contexts, such as diagnosis or tracking recovery, and the new neurological subtests may be more useful in these applications, which were outside the scope of the current study.
This study has several limitations. Firstly, the sample size is relatively small, although the 95% confidence intervals for sensitivity and specificity are not consistent with a clinically significant ability of new subtests to discriminate concussed players. Secondly, there was missing data in some players which could have introduced selection bias. These were predominantly non-concussed cases with normal HIA-1 off-field screening results (n = 17/26), where the neurological sub-tests are highly likely to be normal, suggesting that our results are conservative and are unlikely to have underestimated sensitivity. Thirdly, team doctors administered the SCAT5 in both index test and reference standard assessments, there is a risk of incorporation and diagnostic review bias. Finally, there are no convincing and objective gold standard criteria for the diagnosis of concussion which could lead to outcome misclassification and information bias.
