Our findings provide evidence of sleep disturbances post-TBI in children and adolescents that persisted up to 24 months post-injury. Children with moderate or severe TBI demonstrated the highest scores for sleep disturbance at 24 months post-injury. In comparison, children with mild TBI experienced less sleep disturbance and a tendency toward recovery to pre-injury sleep over time. These findings add to the limited pediatric research on sleep disturbances following TBI. We found a similar persistence in the moderate/severe TBI group as reported in a 48-month longitudinal analysis conducted by Beebe and associates (2007
With regard to risk factors for sleep disturbances, injury severity was a significant predictor of the frequency of sleep disturbances reported by parents. Mild TBI I/II was a significant predictor, but mild TBI III and moderate/severe TBI were not. Similar findings have been documented in the adult literature, where mild TBI has also emerged as a risk factor for sleep disturbances (Beetar et al., 1996
; Clinchot et al., 1998
; Fichtenberg et al., 2000
). While more severe injury was associated with higher overall rates of sleep disturbances in our sample, milder injury was the most predictive factor in a multivariate model with demographic and psychosocial factors. Children with more severe (versus milder) injury may have also had systematic differences in demographic and psychosocial factors that were also related to increased sleep problems. In addition, it has been proposed that persons with mild TBI may have increased recognition of post-injury impairments, and therefore may be more likely to report sleep disturbances as an injury complication. In children with mild TBI, sleep disturbances may also be a symptom of increased awareness of post-injury changes subsequently reported by parents and caregivers. Finally, it is unknown whether there is a physiological or neuroanatomical basis unique to mild TBI injury to account for this finding. Further work is warranted in this area.
Other risk factors associated with sleep disturbances were examined in our TBI cohort, supporting the finding that frequent pain and the presence of psychosocial problems were significant predictors. These same risk factors for disturbed sleep have been identified in various pediatric medical populations, including children with epilepsy, juvenile arthritis, and functional abdominal pain, suggesting some shared risk across medical conditions (Huntley et al., 2007
; Ward et al., 2010
; Wirrell et al., 2005
). Children with acute and chronic medical conditions have an increased risk of sleep disruptions (Hysing et al., 2009
), that are more often chronic and persistent compared to children without medical conditions (Sivertsen et al., 2009
), as shown in this study comparing children with TBI and children with isolated orthopedic injuries. Common mechanisms that may account for the association between sleep problems and medical conditions include underlying disease-related processes (e.g., pain and inflammation), treatment regimens (including medications), hospitalization, and behavioral and psychological factors (Lewandowski et al., 2011
). In the case of pediatric TBI, pain may be a particularly important yet understudied factor contributing to sleep disturbances. It is increasingly recognized that sleep disturbances and pain have a bi-directional relationship (Ohayon, 2005
; Smith and Haythornthwaite, 2004
). Furthermore, the triad of symptoms of sleep, pain, and depression (Chung and Tso, 2010
; Kashikar-Zuck et al., 2010
) may be explained by shared neurotransmitter systems that may be affected after a traumatic brain injury event. In addition to sleep regulation, endogenous factors such as serotonin and hypocretin-1 may also play a role in pain transmission and modulation of depression (Bartsch et al., 2004
; Lautenbacher et al., 2006
). This triad has been described in adults subsequent to a TBI event (Bushnik et al., 2008
; Cantor et al., 2008
; Ouellet et al., 2006
). Further research is needed to identify the mechanisms accounting for disturbed sleep in the pediatric TBI population, which may lead to informed approaches to recognition and clinical management of sleep problems.
Importantly, our findings demonstrated that not only are sleep disturbances likely to occur post-TBI, but that they also are associated with decrements in children's post-injury functioning. This was particularly the case for children with moderate or severe TBI, who may already be struggling with the impact of TBI on physical and cognitive functioning. Further research is needed to better understand the relationship between sleep and outcome parameters such as cognitive function and daytime fatigue, which may also be impacted in children with TBI.
Findings should be interpreted in light of several limitations. First, our measurement of sleep disturbances was limited to a single parent-report question that may not have adequate specificity or sensitivity for identifying the full range of sleep disturbances experienced by children post-TBI. Well-validated questionnaire measures of sleep (such as the Children's Sleep Habits Questionnaire) will be important to use in future studies in the pediatric TBI population to better characterize the specific nature of the sleep problems experienced after injury. The advantage of using this single item to assess for sleep problems is that in a large population cohort it increases feasibility. The validity of a single item of sleep disturbance was examined in a recent study (Gregory et al., 2011
), demonstrating that one item from the Child Behavior Checklist, “trouble sleeping,” was correlated with sleep latency as assessed by sleep diary and actigraphy. Similarly, functional outcome measures were based on parental reports, resulting in common method variance, which is a limitation of this study. For future investigations, the addition of self-report of sleep disturbances and functional outcomes would complement information obtained from caregiver reports. An additional methodological limitation was that only subjective reporting of sleep problems was used to evaluate for sleep disturbances. Ideally, sleep disturbances should be assessed via a comprehensive approach, using parental reports, self-reports, and objective measures (e.g., actigraphy and polysomnography). Finally, this study did not seek to identify the mechanisms of sleep disturbances in terms of neuroanatomical sites of injury or complications such as neurohormonal changes, which may also be important factors in the development of sleep disturbances post-TBI. Despite these limitations, there were several unique strengths of this study, including the longitudinal study design, the large sample size with high follow-up rates, and the inclusion of an orthopedic injury control group.
Our findings highlight the importance of timely evaluation for sleep problems post-TBI in children and adolescents. Furthermore, identification of potentially modifiable risk factors (e.g., pain or mood) may allow for the development of targeted interventions to mitigate the negative outcomes of TBI. Unrecognized and untreated sleep problems in this medically-important population may represent a missed opportunity to improve health outcomes.