The study findings indicate that PCS did not consistently discriminate between children with high- and low-severity mild TBI at different times postinjury. Post hoc analyses revealed that only ratings of individual items from the initial assessment discriminated the high- and low-severity mild-TBI groups. In all other instances, the discriminant scores only differentiated between children with mild TBI and OI. Furthermore, classification accuracy was relatively modest, even for discriminating children with mild TBI from those with OI. At best, only 78% of cases were correctly classified as either mild TBI or OI when ratings of individual items from the initial assessment were used. These results represent a significant improvement on chance classification, but the error rate suggests that PCS ratings cannot be used alone to make diagnostic decisions.
In almost all cases, somatic symptoms showed the strongest correlation with discriminant scores. Somatic symptoms were associated with all functions that discriminated children with mild TBI from the OI group, occurring more frequently and severely in the mild-TBI groups. Moreover, headaches, dizziness, and feelings of the room spinning were among the most discriminating symptoms. In addition, analysis of ratings from the initial assessment suggests that these symptoms discriminated children with mild TBI who sustained an LOC from those without an LOC. Although cognitive symptoms discriminated among groups less successfully than somatic symptoms, both types of PCS correlated with discriminant scores at 3 months postinjury. This finding is consistent with data indicating that cognitive symptoms may increase several months after mild TBI.13
As predicted, discriminant scores derived from individual items displayed better discriminatory power and classification than those produced from summary scores. For instance, discriminant scores based on individual item ratings at the initial assessment discriminated significantly among all 3 groups, but none of the discriminant scores based on summary scores did so. Furthermore, when summary scores were used, sensitivity to detect children with mild TBI who sustained an LOC was substantially lower than when individual items were used. As noted earlier, the symptom summary scores (ie, cognitive and somatic) were based on strong, reliable factors.22
Thus, it is somewhat surprising that the summary scores did not perform as well as individual items. A possible explanation for the better results obtained with individual items is that the differential weighting of items applied in this approach enhances the accuracy of group classification.
Thus, the results suggest that only a subset of PCS have discriminatory power in determining injury severity following mild TBI. Two symptoms in particular consistently emerged as strong discriminators, headaches and dizziness. Previous research has documented the increased prevalence of these symptoms in individuals with mild TBI, and the incidence of these symptoms correlates with later ratings of PCS.23
Headaches are reportedly common following mild TBI, with estimates ranging from 50% to 80%.24
Analysis of post-concussion headache in high school athletes revealed that those individuals experiencing headaches also experienced a greater number of PCS.25,26
Furthermore, individuals experiencing migraine headaches following head injury are more likely to display longer recovery times and more complex concussions.27
Studies have not yet demonstrated a link between injury severity and postural stability deficits, which may be reflected in subjective symptoms of dizziness. Deficits in postural stability have been documented in both adult and child samples, and postconcussion headache has been linked to deficits in balance.28–30
However, it is unclear whether deficits in postural stability can differentiate mild TBI on the basis of injury severity. Recent evidence shows that the acute presence of headaches and postural stability deficits predict postconcussion disorders 3 months postinjury,31
suggesting a link between these symptoms and persistent problems. Furthermore, the worsening of headaches can be used as part of a decision rule to determine the need for neuroimaging following injury.32
The ability to classify severity of a mild TBI from early PCS presentation would be beneficial to clinical care and research. Neuroimaging or neuropsychological evaluation is uncommon following mild TBI unless indications suggest that the injury is complicated. At present, GCS is the primary tool used to determine injury severity, although it is clear that this tool coarsely separates individuals with TBI and cannot differentiate levels of impairment.33
In other words, a clinical need exists for a valid and useful decision rule for diagnosing mild TBI. On the basis of the evidence documented here, early PCS may be a part of such a model. Unfortunately, any attempt at diagnostic classification derived from the current results would have poor sensitivity. Many children with mild TBI with LOC would be misclassified as low-severity mild TBI or even OI. Classification accuracy needs to be increased before PCS can be used clinically to diagnose mild TBI. One possible way to increase discriminatory power is to conduct a more thorough evaluation of the best discriminating symptoms, in this case, headaches and dizziness. Extensive assessment of headaches should include history, family history, and questions regarding type, chronicity, and severity. Postural stability can be quickly and easily assessed by using various techniques designed to assess central and peripheral deficits.28
In the future, we intend to include more detailed assessments of both headache and postural stability in our research in an attempt to improve discriminatory power.
The primary limitation of the study was the inability to include all PCS from the HBI. The sample size was too small to include all 50 variables, so only the cognitive and somatic items and summary scores were used. Although emotional and behavioral symptoms did not cluster together in robust factors,22
specific emotional or behavioral symptoms might increase the accuracy of group classification. Another limitation of the study is the use of LOC as an indicator of injury severity. Although many studies have used LOC as an indicator of injury severity, it is only an indirect indicator of brain abnormalities. As part of the present study, children with mild TBI also underwent MRI of the brain. About 18% of the children with mild TBI displayed neuroimaging abnormalities felt to be trauma-related. When children with and without abnormalities were compared with children with OI in analyses parallel to those presented here, very similar results were found. However, the subgroup of children with MRI abnormalities was small in size (n
= 32) and differed from the other groups in ethnicity and cognitive ability,34
making the results more difficult to interpret. Given the similarity of the findings, only the results using LOC to index injury severity were reported here.
To summarize, the current findings indicate that PCS are able to discriminate between children with mild TBI and OI with modest accuracy. Somatic symptoms appear to have the strongest discriminatory power. Although ratings obtained shortly after injury were able to discriminate between mild-TBI groups as a function of severity, overall classification was relatively poor. Therefore, further refinement of PCS-based measures is needed before relying on PCS to differentiate mild TBI from injuries not involving the head and particularly to differentiate among mild TBIs of varying degrees of severity.