The cerebellum, located in the posterior fossa, plays an integral role in the neural circuits related to cognition, motor function, coordination, equilibrium, emotions, attention, and social functions.1,2 The cerebellum is a primary component of the central vestibular system, which integrates and processes sensory input from the visual, somatosensory, and peripheral vestibular systems.3 Properly functioning central and peripheral vestibular systems are necessary for an individual to coordinate neural output for postural control, spatial orientation, and eye movement control.3 Children who experience damage to the central nervous system may also experience damage to the central vestibular system, leading to delayed gross motor development.3
Children who are treated for posterior fossa lesions have a high rate of survival but also a high likelihood of developing posterior fossa syndrome (PFS). Posterior fossa syndrome is reported to develop in 8% to 25% of children who undergo cerebellar tumor resection and is characterized by postoperative mutism, ataxia, hypotonia, hemiparesis, oculomotor dysfunction, behavioral abnormalities, and neurocognitive deficits.1,4,5 The underlying mechanisms of PFS are not well understood, but proposed risk factors include midline location of the tumor, tumor localization next to the fourth ventricle, length of vermis incision, and young age.2 The syndrome usually manifests 1 to 2 days after surgery and can persist for as little as 1 day or as long as several months to a year.1,4
Children with vestibular-related impairments have poor gaze stability, delayed gross motor skills, impaired postural control, balance deficits, dizziness, and participation restrictions.6,7 Given the clinical presentation of PFS and the involvement of the cerebellum, it is likely that vestibular system dysfunction is contributing to the impairments observed.5 Vestibular rehabilitation (VR) is a type of physical therapy (PT) intervention that includes activities to drive neuroplasticity and central nervous system compensation through the use of specific exercises. Vestibular rehabilitation is effective in improving function of both children and adults with vestibular disorders.3,7,8 Currently, the treatment of PFS includes supportive care, which often involves speech therapy, occupational therapy, and PT.9 While VR exercises have been adapted for use in children with peripheral vestibular dysfunction,3,10 there is currently no research exploring the effectiveness of VR on symptoms of PFS. Thus, the purpose of this case report is to describe the use of VR in combination with standard balance training and developmentally appropriate PT activities to improve gaze stability, postural control, and balance for a child with PFS secondary to juvenile astrocytoma mass resection.
DESCRIPTION OF THE CASE
The participant's mother provided informed consent for medical treatment, as well as case report presentation. All information was gathered through parent interview, medical record review, and pre- and postintervention assessments. The focus of this case report is on a 3-year 10-month-old girl who was developing typically until she was diagnosed with a posterior fossa mass and moderate supratentorial hydrocephalus with mass effect on the brainstem at 3 years 4 months of age. Prior to diagnosis, she began experiencing left facial nerve palsy and ataxia. She was taken to the emergency department and imaging revealed the posterior fossa mass. After diagnosis of juvenile pilocytic astrocytoma, she underwent craniotomy and surgical gross total resection of the mass. Posterior fossa syndrome developed following successful removal of the mass. The child received outpatient speech therapy once per week for treatment of dysphagia following resection. Six months after surgical resection, she was referred to outpatient PT secondary to continued symptoms of PFS, including balance deficits and gross motor delays that continued to limit her safety, function, and participation in age-appropriate activities. She was not using adaptive equipment at the time of intervention. Her medications included acetaminophen (15 mg/kg by mouth as needed), hydrocortisone (10 mg 2 times per day during illness), ibuprofen (5 mg/kg by mouth as needed), and levetiracetam, an antiseizure drug (1.6 mL by mouth 2 times per day). The child attended a preschool 5 days per week and was a playful, energetic child.
Pre- and postintervention assessments were completed by a board-certified clinical specialist in pediatric PT. A board-certified clinical specialist in neurologic PT and advanced training in VR assisted with the initial assessment. Both assessments took place at a community-based pediatric therapy clinic and lasted approximately 1 hour. Physical examination included analysis of posture; clinical observation of functional movement and gross motor skills; and standardized assessment of balance, postural control, and vestibular function. Participation was voluntary, and the child's insurance was billed for the 10-week intervention program. All treatment sessions took place at the child's preschool.
Outcome measures used for the pre- and postintervention assessments included the Pediatric Balance Scale (PBS), Modified Clinical Test of Sensory Interaction on Balance (MCTSIB), Dynamic Visual Acuity (DVA) test, and Head Impulse Test (HIT). The PBS and the MCTSIB were used to assess balance and postural control. The DVA and the HIT were used to assess gaze stability and functioning of the vestibulo-ocular reflex (VOR). The MCTSIB, HIT, and DVA were administered at visits 1 and 20. The PBS was administered at visits 3 and 20.
Pediatric Balance Scale
The PBS was developed for pediatric use based on the adult Berg Balance Scale and is a 14-item measure used to evaluate balance in children.11,12 Good to excellent test-retest reliability of the PBS has been reported for both children developing typically and children with mild to moderate balance dysfunction.11
Modified Clinical Test of Sensory Interaction on Balance
The MCTSIB is an outcome measure used to evaluate postural control under various sensory conditions.13 To perform the test, the child was asked to stand with her hands at her side in the following conditions: (1) firm surface with eyes open; (2) firm surface with eyes closed; (3) foam with eyes open; and (4) foam with eyes closed. The child's performance was timed for up to 30 seconds in each position. The mean of each of the 3 trials was summed to create a total score. The MCTSIB has a total score of 120 points. A score of less than 110 indicates a potential vestibular problem.14 Test-retest reliability of the MCTSIB in children developing typically and those with vestibular hypofunction has been reported as good (ICC ≥ 0.73) for all test conditions except condition 4.14
Dynamic Visual Acuity Test
The DVA is a noninstrumented test used to examine gaze stability by assessing function of the VOR.10,13 The DVA test is reported to be a reliable test of gaze stability in children as young as 3 years old.14 To perform the DVA test, the child sat 10 ft away from the Lea Symbols chart. The chart had 5 symbols (ie, circle, square, house, apple) on each line. The child was asked to identify the symbols, starting at the top of the chart, and continued naming symbols until she missed more than 2 symbols on 1 line. This was performed under 2 conditions: (1) head stationary and (2) neck flexed 30° and passively rotated, by the physical therapist, 15° right and left to a metronome set to 2 Hz. The lowest line that the child could read correctly (not missing more than 2 symbols) was recorded for each testing condition. The DVA score was calculated by subtracting the difference between the static and dynamic testing condition scores. A difference of more than 2 lines is indicative of potential vestibular-related impairments.6,13,14
Head Impulse Test
The HIT is an examination used to identify hypofunction of the peripheral vestibular system.6 To complete the HIT, the child's neck was flexed approximately 30°, and she was asked to keep her eyes fixed on the examiner's nose while the examiner rapidly turned the child's head 5° to 10° to the right or left. The HIT was repeated 3 times to each side in random order.6 With an intact peripheral vestibular system and functioning VOR, the child should be able to keep her eyes fixed on the examiner's nose. If the child's gaze is not stable and a corrective saccade to return her gaze back to the target at the end of the head thrust is noted, peripheral vestibular hypofunction is suspected.6,15
DESCRIPTION OF INTERVENTION
The child began PT 6 months after surgical resection of the posterior fossa mass. Dosing was based on the available literature, which suggests that VR exercises should be performed up to 20 minutes total per day, for the duration of at least 6 weeks.16–18 Therefore, the child was seen by a physical therapist 2 times per week for 60 minutes per session for a total of 20 visits. Each PT session included approximately 40 minutes of developmentally appropriate gross motor activities. Table 1 provides examples of these activities. The remaining 20 minutes of each session were dedicated to VR, primarily gaze stabilization exercises. The specific interventions performed each day depended on the child's attention, interest, and compliance. All interventions were adapted to be fun and engaging for a young child. Vestibular rehabilitation exercises were progressed by increasing the repetitions or difficulty of each activity. If she was unwilling to complete additional repetitions, due to boredom with the activity, then an exercise was made more challenging by increasing the speed of the objects (ie laser, marbles, small pictures) to be tracked or identified. Exercise difficulty was also progressed by incorporating the VR exercise into a higher-level functional skill such as walking, sliding, or riding a bike. Combining specific rehabilitation exercises with age-appropriate gross motor skills provided the child with opportunities to practice gaze stabilization in a functional context. Activities in Table 2 are organized according to progressive difficulty for this child. The child's home exercise program included (1) standing on a compliant surface (ie, foam, pillow, mattress) while singing a song with arm movements, (2) identifying pictures in a book with 10 head turns in the yaw and pitch planes, and (3) tossing and catching a medium-sized playground ball.
The child walked independently but had difficulty running with appropriate speed and form, secondary to balance deficits and left lower extremity weakness. She inconsistently veered to the left while walking and running. She was unable to perform tandem walking and required use of a handrail to climb stairs using a step-to pattern. She would not attempt to jump down from an elevated surface and was unable to successfully catch a playground ball using only her hands. Frequent falls, especially when she was moving quickly through space (ie, running, jumping, bending over to pick up items), were also noted. She was able to follow directions and willingly attempted a variety of activities.
The child's score on the MCTSIB was within normal limits. Scores on the PBS, DVA, and HIT identified deficits at the body structure and function level. Case data are shown in Table 3.
POSTINTERVENTION ASSESSMENT AND OUTCOMES
The child jumped down from a 7-in step and forward 6 to 12 in without loss of balance upon landing. She briefly maintained single-leg stance to step over objects and kick a ball without falling. She negotiated a 6-in wide balance beam independently. Veering left and falling while walking and running decreased.
Pediatric Balance Scale
Her PBS score increased from 41 to 48 out of 56 points, an increase of 7 points between the pre- and postintervention assessments (Table 3). Her scores improved on items assessing both static and dynamic balance, including standing with 1 foot in front of the other, standing on 1 foot, turning to look behind, and reaching forward. While her postintervention assessment score of 48 is below the mean score of 4-year-old girls developing typically, her score was within 1 standard deviation of the mean.19
Modified Clinical Test of Sensory Interaction on Balance
Her MCTSIB score decreased from 110 to 96 points (Table 3). She had difficulty focusing on this test at postintervention assessment, requiring multiple verbal cues to attend to task. Her score decreased on the basis of her performance on conditions 3 and 4 of the MCTSIB. However, the physical therapist noted improvements in the child's balance and postural control under various sensory conditions throughout the intervention period. For example, on the first day of treatment, the child required contact guard assistance to maintain static standing on foam while completing an 8-piece puzzle. By the end of the intervention period, she was able to stand independently on foam while weight shifting to reach 8 puzzle pieces.
Dynamic Visual Acuity Test
While the child's DVA test score improved by 1 line at the end of the intervention period, the results of the DVA at postintervention assessment continued to fall in the abnormal range (Table 3), indicating dysfunction of the child's gaze stability, mediated by the VOR. At preintervention assessment, she had 5 lines of difference between her static and dynamic testing conditions. At postintervention assessment, she only had 4 lines of difference between static and dynamic testing conditions and could correctly read 1 line lower in the static condition.
Head Impulse Test
Upon completion of the intervention period, the child continued to present with an abnormal HIT to the left (Table 3), indicative of unilateral peripheral vestibular dysfunction on the left. While peripheral vestibular dysfunction was not initially suspected based solely on her diagnosis, the corrective saccade noted when her head was quickly turned to the left was a consistent response and believed to be an accurate finding.
A 3-year 10–month-old girl with PFS secondary to cerebellar juvenile pilocytic astrocytoma tumor resection received a total of two 60-minute PT sessions per week for the duration of 20 visits. Her physical therapist incorporated VR exercises and balance training in addition to age-appropriate gross motor therapeutic activities.
Following intervention, the child's balance abilities, based on the PBS, improved. At preintervention assessment, her PBS score of 41 was 7.5 points away from the mean PBS score of 3.6- to 3.11-year-old girls developing typically.19 Her postintervention assessment score improved to 48, which is approaching the mean score of 51.2 for girls between 4.0 and 4.5 years of age who were developing typically.19 While the minimal clinically important difference for children with PFS is not available, her PBS score improved by 7 points, which exceeds the PBS minimal clinically important difference score reported for children with cerebral palsy at 5.83 points.20 Furthermore, functional improvements in the child's balance were noted, as previously described.
The MCTSIB has been used to examine postural control in school-aged children and is recommended for use in children with suspected vestibular-related impairments; however, no published research has used the MCTSIB with preschool-aged children.6 During the postintervention assessment, she had difficulty following directions and giving her best effort on 2 conditions (standing on foam with eyes open and closed) of the MCTSIB. Scores on these conditions decreased. Condition 4 on the MCTSIB is reported to have the lowest test-retest reliability (ICC = 0.56).6 Thus, we suggest the results of condition 4 on the MCTSIB be viewed with caution. Further research is needed to determine the reliability and validity of this outcome measure when used with children younger than 6 years.
While this child's postintervention assessment DVA test score indicated that she still had dysfunctional gaze stability, she was able to correctly read 1 line lower on the static testing condition and 2 lines lower on the dynamic portion of the postintervention assessment DVA test, indicating that improvements in visual acuity and gaze stability had occurred. Braswell and Rine10 reported similar improvements in a child with acquired vestibular hypofunction following completion of a 6-week bout of visual-vestibular exercises, indicating that gaze stabilization exercises may lead to positive changes in children with peripheral and central vestibular-related impairments.
Dysfunction in unilateral peripheral vestibular dysfunction, as measured by the HIT, was initially not anticipated because of the assumption that this child would only present with central vestibular deficits secondary to the cerebellar location of her tumor. However, Camet et al13 reported that children treated for brain tumors have a significant risk (P = .009) of failing both central and peripheral vestibular screens, including the HIT test, due to the exposure to ototoxic chemotherapy agents used for brain tumor treatment. The child in this case study was not exposed to either chemotherapy or radiation, yet she had peripheral vestibular dysfunction during pre- and postintervention assessments. While she may have had peripheral vestibular dysfunction prior to the development of PFS, this finding highlights the need for physical therapists to conduct vestibular screening on pediatric patients treated for brain tumors.
The body of literature related to dosing of VR for children is limited. The available research suggests that VR exercises, in order to be effective, should be performed 3 times per week for 20 to 30 minutes for the duration of 6 to 10 weeks.17,18 Adult clinical practice guideline suggests that gaze stabilization exercises should be performed 2 to 3 times per day.16 The dosing of this child's VR program was designed while taking into consideration constraints imposed by insurance coverage regarding the number of PT visits. While the child did complete VR exercises 2 times per week for 20 minutes for the duration of 10 weeks, her overall outcomes may have been improved if dosing had been increased to 3 times per week and/or if exercises had been performed multiple times per day. The child was provided with a home program, but home practice of exercises was inconsistent and progression of home exercises did not occur.
The results of this case study should be interpreted with caution, as the outcomes of a single-subject case study have limited generalizability to a larger population. While this child did show improvements in balance and gaze stability, her plan of care ended prematurely, potentially before maximal improvements could have been made, due to the child moving to a new preschool in a different town. However, the description of this case suggests that both central and peripheral vestibular dysfunctions may accompany PFS in children treated for brain tumors and adds to the growing body of evidence that VR is safe and can be effective in reducing symptoms of vestibular dysfunction in young children. Additional research with larger sample sizes is needed to determine the optimal dosing and therapeutic intervention design of VR required for maximal improvements in balance, postural control, and gross motor skill performance in children with PFS. Finally, exploring a longer duration (>10 weeks) and earlier initiation of VR and developmentally progressive PT post–tumor resection (sooner than 6 months postoperative) could be useful to determine whether better outcomes could be achieved.
WHAT THIS CASE STUDY ADDS TO EVIDENCE-BASED PRACTICE
This study was the first assessment of vestibular dysfunction and a clinically designed VR plus PT program for a child with PFS resulting from brain tumor resection. Our results support the use of VR and balance activities that are adapted to be fun and engaging for young children. The outcome measures and interventions used in this case report can be easily replicated by pediatric physical therapists in a variety of settings.
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