The present findings support the hypothesis that children with mTBI have PCS that can not be accounted for by the effects of traumatic injuries more generally or by pre-existing symptoms. Controlling for preinjury symptoms, parent ratings of somatic and cognitive PCS and parent-based counts of PCS were higher in children with mTBI than in children with minor OI. The results illustrate the benefits of examining different types of PCS and of considering variations in these effects in relation to time since injury and injury and non-injury characteristics. Group differences in parent ratings of somatic PCS and counts of PCS were most evident at the initial follow-ups and had resolved by 12 months post injury. In contrast, parent ratings of cognitive PCS in children with mTBI did not peak until the 3-month assessment and remained higher for these children than for the OI group throughout the follow-up period. The parent ratings confirm our expectations that changes in PCS after mTBI vary for different types of symptoms and suggest that some types are more persistent than others.
Similar to results for the parent-based measures, child self-report revealed higher ratings of somatic PCS in the mTBI group only at earlier in follow-up, with children in the two groups endorsing similar levels of physical complaints by 3 months post injury. However, like parent ratings of cognitive PCS, the mTBI group had higher self-reported counts of PCS than the OI group across the follow-up interval. Correlations between child and parent reports of PCS provide consensual validation for the findings. The consistency of child self-ratings of somatic PCS and counts of PCS with the corresponding parent data also helps to establish the validity of self-report in 8- to 15-year-old children.
Consistent with previous studies and with high base rates of PCS in the general population, PCS were evident in children with OI as well as in those with mTBI (Bijur & Haslum, 1995
; Gasquoine, 1997
; Goldstrohm & Arffa, 1995; Kashluba, Casey, & Paniak, 2006
; Meares et al., 2006
; Light et al., 1998
; Wong, Regennitter, & Barrios, 1994
). Early in follow-up, both groups showed increases in parent ratings of cognitive PCS and decreases in ratings of somatic PCS and in counts of PCS, suggesting that some symptom changes after mTBI reflect responses to injury more generally rather than effects of brain insult.
Also in keeping with past studies, PCS were related both to injury characteristics and non-injury factors (Kirkwood et al., 2008
). Higher levels of preinjury symptoms predicted higher scores on all corresponding measures of PCS. Other associations included younger age and female sex with higher parent counts of PCS; lower SES and female sex with higher child self-ratings of somatic PCS; and lower SES and older age at injury with higher child self-ratings of cognitive PCS. Although these associations were evident for both groups of children, they underscore the importance of considering non-injury background characteristics in evaluating PCS in children with mTBI.
Several injury characteristics assumed to reflect greater risk for brain insult predicted higher levels of PCS within the mTBI, including LOC, acute CT scan abnormality, parenchymal lesion on MRI, hospitalization, MVRT, and injuries to body regions other than the head (Falk et al, 2006
; Levin et al., 2008
; Luis et al., 2003
; McKinley et al., 2002
; Ponsford et al., 2000
; Yeates et al., 2009
). The effects of LOC and MVRT were observed throughout the follow-up interval, suggesting that persisting symptoms are more likely in children with higher-risk head injuries. These findings highlight the need for further investigation of ways to grade injury severity in this population and are consistent with suggestions that a minimal level of severity may be necessary for head-injury-specific PCS (Asarnow et al., 1995
; Satz et al., 1997
We recently found that MRI abnormalities were associated with higher parent ratings of cognitive PCS, but only in children with lower cognitive ability (Fay et al., in press
). The present findings indicate that this association may extend to the broader mTBI sample when abnormalities are defined in terms of parenchymal lesions. These findings are also consistent with adult data showing greater cognitive deficits following complicated compared with uncomplicated mTBI (Williams et al., 1990
). It is unclear why parenchymal lesions on MRI predicted more cognitive PCS only at the 3-month assessment, but higher rates of MVRT (implicating more severe mTBI) in children with lower SES may explain why the association of brain lesions with cognitive PCS was evident only in this subset of the TBI group. The association of acute CT scan abnormalities with higher parent ratings of emotional PCS is also consistent with previous findings (de Andrade et al., 2006
; Levin et al., 2008
). In the present study, both this association and that between LOC and parent counts of PCS were more evident for children injured at younger ages. This age-at-injury effect is similar to that observed in studies of other outcomes of pediatric mTBI (Gronwald et al., 1997
; McKinlay et al., 2002
) and suggests that younger age at injury increases risks for PCS.
The results of this study accord well with the hypothesis that both neurological and psychological factors contribute to PCS in children with mTBI (Alexander, 1997
; Binder, 1986
). An implication of post-injury changes in PCS in both injury groups is that the experience of trauma or factors not specific to head injury, such as physical discomfort or difficulties in adjusting to the effects of injury, are likely to contribute to PCS after mTBI. Consistent with findings from both animal and human studies (Bigler, 2008
), neurological disruption may result in problems in functioning that precipitate or add to these effects, at least in a minority of children with mTBI (Kasluba et al., 2008
; Massagli et al., 2004
; Ponsford et al., 1999
; Ponsford et al., 2000
; Yeates et al., 1999
). An alternative possibility is that group differences reflected greater expectancies for behavior change after injury to the head than after other injuries (Ferguson, Mittenberg, Barone, & Schneider, 1999
; Gunstad & Suhr, 2001
), though the association of injury factors to PCS within the mTBI group argues against such an interpretation. More definitive support for a neurogenic component of PCS will require investigation of associations of subjective symptoms with residual injury-related changes in brain structure or function (Bigler, 2008
; Kibby & Long, 1996
). Potential influences on PCS of children's coping skills and of neural “reserve” (Dennis, Yeates, Taylor, & Fletcher, 2007
) may also need to be considered, as these characteristics may obscure the effects of demonstrable brain insults.
A major limitation of the study is that information regarding the children's status at the time they presented to the ED was determined by retrospective review of medical records rather than via structured procedures for intake and evaluation. Substantial inter-individual variability likely exists among ED health care providers in methods of evaluating children with minor traumatic injuries and in details regarding the injury and the child's current medical status included in the medical record. Reliance on these data constrained our ability to assess injury factors in a more uniform and probing manner and to detect relations between injury factors and PCS. A further weakness is the lack of a non-injury comparison group (Satz et al., 1997
). Inclusion of an uninjured group would have been useful in clarifying child and family characteristics associated with minor traumatic injuries and in providing a yardstick against which to assess the extent of post-injury PCS in both the mTBI and OI groups. A third limitation is that the MRI procedures employed in this study, although selected to be the most sensitive available at the time the study was designed, may have been insensitive to some of the subtle insults associated with mTBI. Scans conducted soon after injury or methods more sensitive to white matter injury, such as diffusion tensor imaging or susceptibility-weighted scans, may provide for a more sensitive assessment of neuropathology (Bigler, 2008
Although we have recently demonstrated that persisting effects of PCS occur in a minority of children with mTBI (Yeates et al., 2009
), further research is needed to find ways to identify these children, isolate the neural and cognitive correlates of their problems, and determine the implications of these symptoms for children's behavior, learning, and daily functioning. A focus on individual symptoms that distinguish children with mTBI from other traumatic injuries at a point at which more transient symptoms have resolved may be one useful strategy (Kashluba et al., 2006
: Overweg-Plandsoen et al., 1999
). Another way to advance this goal is to examine other potential risk factors. As an example of this approach, we are currently examining pre-injury child behavior and the family environment as moderators of group differences in PCS in the present sample. Investigation of the mechanisms responsible for persistent PCS is also essential. Persistent cognitive deficits that are subtle and present in only a minority of children may help to account for the largely negative results of well-controlled studies of the cognitive outcomes mTBI (Beers, 1992
; Cassidy et al., 2004
; Satz et al., 1997
). Another possibility is that children have problems coping with initial the cognitive or physical effects of injury, and that these adjustment difficulties perpetuate problems in functioning even in the absence of brain-based cognitive weaknesses (Gasquoine, 1997
Research on the psychosocial outcomes of mTBI would also profit from closer examination of family consequences of these injuries. Study of family outcomes at baseline and 3 months in the present sample revealed only a temporary increase in burden among families of children with mTBI compared to those of children with OI (Ganesalingam et al., 2008
). However, because higher levels of PCS at baseline were associated with greater family burden and distress in both injury groups, PCS may be of clinical concern even if not specific to head trauma. Additional research is required to determine if families are adversely affected by persistent PCS, if the longer-term burden of mTBI is greater than that associated with other traumatic injuries, and how to help families and children manage these symptoms.
In conclusion, these results add to the existing literature and our previous report on postinjury changes in PCS (Fay et al., in press
; Yeates et al., 2009
) in several ways. They reveal that: (1) while postinjury changes in PCS are observed following mild traumatic injuries other than mTBI, these changes are more pronounced in children with mTBI; (2) different patterns of change over time post injury are evident for different types of PCS; (3) negative effects of mTBI on PCS are evident on child self-report as well as on parent ratings; (4) multiple indicators of mTBI severity are associated with more PCS following mTBI, including MVRT, LOC, hospital admission, acute CT scan abnormality, parenchymal abnormality on MRI, and accompanying non-head injury; and (5) the effects of mTBI on PCS are moderated by non-injury factors such as age at injury and SES. These findings imply a need for more careful monitoring of PCS in children after mTBI, including efforts to distinguish among different types PCS, as well as for additional studies of injury and non-injury factors that place children at risk for persistent symptoms. Further research is required to investigate factors useful in identifying individual children who are most likely to experience elevations in PCS after mTBI and to examine the relation of these symptoms to learning or behavior problems. Nevertheless, our results provide initial clues regarding potentially useful injury and non-injury markers of increased risk, supporting the possibility of targeting subsets of children for closer post-injury monitoring. Larger-scale investigations of the neurological, neuropsychological, and psychosocial dimensions of PCS that employ rigorous research designs are imperative for further progress in this area (Carroll et al., 2004
). As the vast majority of children with mTBI and other minor traumatic injuries are released from the ED without systematic follow-up (Hawley, 2003
; Kirkwood et al., 2008
), the promise of this research is improved methods to monitor, identify, and treat the sequelae of mTBI and other traumatic injuries.