Concussion, or mild traumatic brain injury (mTBI), is a common injury, with national estimates of more than 2 million TBI-related outpatient visits to the emergency department (ED) in 2014, of which 812,000 occurred in children 0-17 years of age.¹ In recent years there has been increased attention centered on concussion; however, it has been mostly focused on sports concussions in older youth and young adults, with less attention on the concussion burden in early childhood, especially those 0-4 years of age. Children ages 0-4 have the highest rates of ED visits for TBI of all severities across the pediatric age span^1,2 and have increased risk compared with older children for ongoing cognitive and behavioral effects of TBI because of their developmental stage.^2-9 Recent reports have documented differences in cognitive functioning, behavioral regulation, and emotional functioning in young children within and beyond the first year post-TBI, including mTBI,^10-12 highlighting the importance of recognition and diagnosis at the time of injury. Much of the research in early childhood has focused on moderate-to-severe TBI, with less attention on the burden of concussion on children in this age group.

Young children who experience concussion pose a unique diagnostic challenge for clinicians due to the developmental limitations on subjective patient symptom recognition and report, the mainstay of concussion diagnosis. Tools developed for concussion diagnosis and management have been suitably validated for older children who are capable of symptom self-report. For example, the Graded Symptom Checklist (GSC), Acute Concussion Evaluation (ACE), Post-Concussion Symptom Scale (PCSS), Post-Concussion Symptom Inventory (PCSI), and Child SCAT-5 (Sport Concussion Assessment Tool 5- Child Version) have been validated for children ages 5 and up.^13,14 However, these assessment scales have limited usefulness for this 0-4-year age group where verbal skills are non-existent or emerging. This results in a heavy reliance on report of signs and symptoms from parents/caregivers, who have been shown to report fewer symptoms in preschool children compared with parents of school-aged children, or only report readily observable symptoms (e.g., loss of consciousness or vomiting).^15,16 In a study relying on parent report of symptoms, children younger than 6 years were reported to have faster resolution of concussion symptoms, compared with school-aged children, although it is not clear if this is due to differences in the injury or the limitations of parental reporting.¹⁷ In a small sample of 28 pre-school children with concussion, Suskauer et al, described a broad spectrum of reported symptoms including appetite changes, behavioral dysregulation, decreased engagement, enuresis, increased dependence, and stomachaches, which are not typically associated with concussion or included on traditional concussion symptom scales.¹⁸ A more comprehensive understanding of the characteristics of concussion in children 0-4 years of age would improve diagnosis and management in these very young children by providing insight into the mechanisms of injury, symptom profile, typical location of presentation for care, and clinical course of care. Thus, the purpose of this study was to comprehensively describe the natural history and presentation of concussion in early childhood, specifically ages 0-4 years.

Concussion in early childhood among children 0-4 years of age remains a diagnostic challenge for clinicians, and many may feel ill-equipped to care for concussion in this young population.^21,22 Findings from this study, one of the most comprehensive descriptions of children 0-4 years of age with a diagnosed concussion, provide valuable insight into characteristics of concussion in this early childhood population during their course of care. Awareness of this information by clinicians may, in turn, facilitate improvements in diagnosis and clinical management.

Symptom report is the current cornerstone of concussion diagnosis, often through the use of concussion symptom scales, such as the PCSS; however, most scales have only been validated for children over the age of 5.^23,24 In our study sample, most patients were found to have 1-3 distinct symptoms that are included on the PCSS, and those reporting the greatest number of symptoms (>6) were children 2-4 years of age. Current concussion symptom scales, like PCSS, contain abstract concepts (e.g., feeling mentally “foggy,” feeling slowed down, nervousness, difficulty concentrating) that could be difficult for very young children to comprehend or verbally express, leading to heavy reliance on parent/caregiver reports. Similar to previous work¹⁵, the fewer number of symptoms reported in those less than 2 years in our study may suggest either a lower symptom burden or under-reporting or under-recognition of symptoms by parents/caregivers for the youngest children in our cohort.

Our study found that children 0-4 years of age do present with similar symptom categories as older children and adolescents. Almost one-third of patients reported at least one somatic symptom, with almost half of patients reporting sleep symptoms, similar to findings by our group in older children.²⁵ Further, visio-vestibular symptoms were also common in our study sample (20.4%). Previous studies by our group have shown the visio-vestibular exam can be reliably completed in those as young as 10 years and by approximately 50% of 6-year-olds.^26,27 While clinicians may attempt to assess these deficits in 2-4 year-olds, developmental limitations present a challenge in testing this population (e.g., assessing balance and eye tracking).

Importantly, our study confirms and extends the work of others^15,17,18 by examining a larger cohort of concussed patients in early childhood and adding a description of concussion in children less than 2 years of age. The results reinforce previous findings¹⁵ that patients and/or parents/caregivers will often report symptoms not commonly captured on standard concussion symptom scales, with “personality change” as the most common in our study. Other behavioral changes reported by parents/caregivers included increased crying, increased neediness or attachment to parent/caregiver, increased meltdowns, regressive behaviors, decreased interaction, and increased frustration. Additional symptoms reported that are not part of typical concussion scales include increased/decreased appetite, increased/decreased urination, urination accidents, and constipation/diarrhea. These types of symptoms are not frequently reported among cohorts of older children, highlighting the importance of incorporating a behavioral change assessment into the clinical concussion assessment in very young children. These findings support the need for the establishment of developmentally appropriate diagnostic tools tailored to early childhood. Symptom scales for very young children should include common concussion symptoms observed across all ages, but should also include additional symptoms specifically observed in this age group in order to improve the recognition, diagnosis and management of concussion.

Our study also found that more than three-fourths of patients diagnosed with a concussion presented to the ED or urgent care for initial care; the majority presented on the same day of injury, especially those <2 years of age. The remaining patients generally presented within one week of injury. These findings confirm previous work done by our group; the most common point of entry into the CHOP healthcare network for this age group was found to be the ED followed by the primary care setting.¹⁹ Those less than 2 years of age are at risk for skull fractures and more serious brain injuries,^28,29 and their most commonly-experienced symptoms of concussion (e.g., vomiting) could also be suggestive of a more serious traumatic brain injury, prompting parents to seek immediate evaluation in an ED.

In this setting, clinicians often rely on radiological imaging to exclude more serious TBI or trauma, particularly in very young children. Consequently, it is not surprising that a large proportion of our study sample received radiological imaging, even though the majority (88.3%) were found to have normal radiological findings. The use of head injury clinical decision rules has made significant headway in decreasing unnecessary radiation exposure for children,^30,31 however, they are not intended for use in children under the age of 2 years. Further research is needed to determine if there are well-defined circumstances in the 0-2 year population where imaging can be avoided.

Due to recent increased public awareness, pediatric concussion is often thought of primarily in relation to organized sports. However, children 0-4 years of age engage in different types of activities resulting in different mechanisms of injury compared with older children.²⁰ Broadly, the most common mechanism of injury in our study population was a fall, which is consistent with prior literature.^1,32 The most frequent fall scenarios that provide an opportunity for injury prevention were those from furniture or down stairs and these data suggest providers should consider evaluation for a concussion whenever children present with these injury histories. This pattern of injury in this age range also provides potential opportunities for prevention, such as anticipatory guidance regarding the need for gates at the top of stairs in homes with young children.

There are several limitations to note for this study. First, as a retrospective cohort study, data variables were not collected as systematically as in a prospective study. Consequently, the frequency of particular symptoms may be underrepresented if they were not uniformly assessed especially for those symptoms that are not part of common scales such as the PCSS. In addition, symptom prevalence, specifically vestibular symptoms, may be a conservative estimate for this population as most children in this age range present to the ED and may not be systematically assessed. However, shortly before the beginning of our study period, CHOP implemented clinical decision support tools into the EHR and network wide training to increase systematic symptom assessment and clinical documentation of concussion care.³³ Second, our sample may not be generalizable to all early childhood concussion since it only includes children who sought some type of care within the CHOP Network. Characteristics, clinical course, and management may differ among children seen outside of the CHOP healthcare network. The sample primarily represents a suburban and urban population with access to a specialized children’s hospital and pediatric ED, which may not be representative of all geographic areas. Third, the study used ICD-9-CM diagnostic codes in the EHR to identify concussed patients. The lack of clear diagnostic criteria for concussion in young children may have resulted in providers erroneously using other diagnosis codes or misdiagnosing cases of concussion, thus resulting in our study potentially missing some true concussions.

In summary, this study is the most comprehensive characterization of concussion in early childhood, 0-4 years, to date. Despite improvements to concussion diagnosis and management in older children and adolescents, young children with concussion remain a diagnostic challenge. Importantly, while young children frequently present with symptoms similar to those observed in their older counterparts, many experience symptoms not included in tools validated for older ages. In addition, unlike older children, the diagnosis of concussion in children 0-4 years relies heavily on parent/caregiver symptom reporting. Symptoms commonly reported in very young children include changes in behavior, personality, appetite, and urinary/gastrointestinal systems; standardized assessment tools for concussion in early childhood should be developed so as to account for these symptoms. While clinicians can diagnose concussion in early childhood using existing tools validated for older children, assessment of these additional symptoms observed in this very young age group may further support the diagnosis, thereby improving identification and management of concussion in this vulnerable population.