As an infant, "Sam" was diagnosed with congenital, profound hearing loss due to Mondini malformation, an inner-ear abnormality. Following a hearing aid trial, he received a left-sided cochlear implant when he was 21 months old. But despite Sam's significant gross motor developmental delays—he could not sit independently until 18 months, stand independently until 24 months, or walk independently until 30 months—no one recommended an evaluation of his vestibular system.
At age 17, Sam was still unable to ride a two-wheeled bike. We recently saw him at the Boys Town National Research Hospital clinic for a vestibular evaluation. We learned that Sam has no vestibular input, and diagnosed a global, bilateral vestibular loss. After identifying his vestibular loss, we found his visual acuity to be abnormal during head movement.
Sam has never received physical therapy. But if he had, many of his functional deficits could have been addressed and potentially improved: Vestibular rehabilitation exercises can help improve visual acuity, reading acuity and gross motor developmental delay. Unfortunately, at the time of Sam's initial diagnosis, vestibular testing was virtually nonexistent—clinicians typically neither recommended nor performed vestibular tests on children with hearing loss.
Until recently, vestibular function in children has received little attention clinically or in research. This inattention is perhaps due to the low incidence of vestibular loss in typically developing children, and the fact that not all children with hearing loss have vestibular loss. But the association between vestibular and hearing loss is significant: Vestibular loss is present in approximately 50 percent of children prior to cochlear implantation. There is a small risk—about 10 percent—for additional vestibular loss following cochlear implantation, as a result of the surgical procedure. Vestibular loss is also more likely to occur as hearing loss becomes more severe.
Vestibular loss is commonly associated with meningitis, cytomegalovirus, inner ear anomalies and connexin 26 mutations, among other conditions. Given this information, audiologists, speech-language pathologists and physicians should suspect vestibular loss in children with these diagnoses and in children with more severe hearing loss. According to these criteria, Sam would have been considered at risk for vestibular loss because his hearing loss was profound and due to an inner ear anomaly.
Many children with vestibular loss do not complain of dizziness. Rather, the condition may present as gross motor developmental delay, and later as reductions in visual acuity. Vestibular rehabilitation exercises can help—if they are recommended. But vestibular rehabilitation is generally not recommended unless vestibular loss is diagnosed—and vestibular loss cannot be diagnosed without appropriate testing.
Vestibular tests and modifications
Despite the relatively strong association between hearing and vestibular loss, there are no guidelines for performing vestibular tests on children with hearing loss. Unfortunately, this means that some children with vestibular loss—like Sam—do not receive testing that could help ameliorate developmental delays.
Fortunately, even in the absence of such guidelines for children, most vestibular function assessments used for adults can also be used with younger patients, with some general modifications. Here are brief descriptions of vestibular tests with recommended modifications for infants and children.
Bedside test. The bedside test is a quick way to obtain preliminary information about the vestibular system—both central and peripheral—with very little equipment. An ocular motor assessment (smooth pursuit, saccades, nystagmus direction, ocular range of motion, etc.) and a quick vestibular assessment (head impulse, head shake, Clinical Test of Sensory Integration on Balance, etc.) can all be completed bedside. For children—given limited assessment time or a lack of readily available equipment—the bedside test results can tell us whether we need to refer for more comprehensive tests.
Modifications to the bedside test include the use of finger puppets or stickers for visual targets, as well as the use of "fun glasses" that prevent the use of vision for head shake or the Clinical Test of Sensory Integration on Balance. Audiologists may attempt bedside assessments on children of all ages. Generally, we find that children older than 3 can complete a full bedside exam.
Vestibular evoked myogenic potentials. These assessments of otolith function come in two varieties: cervical and ocular. The ocular and cervical VEMP are particularly helpful in testing children as they provide ear-specific information about the utricle and saccule, are quick to administer and do not induce dizziness. VEMP responses are electromyograms, meaning they measure changes in muscle activity. As discussed in the sidebar (see below), the vestibular system is responsible for initiating a variety of reflexes, and the VEMP uses these reflex pathways.
The cervical VEMP is a measure of saccule function and is measured by putting an electrode on either side of the neck, specifically on the sternocleidomastoid muscle (see photo 2). A loud acoustic stimulus is presented to the ear, causing the neck muscles to relax from contraction. The ocular VEMP is a measure of utricle function, and is measured by putting an electrode under the eyes. Just like the cervical VEMP, a loud acoustic stimulus is presented to the ear, but this time it causes the muscles under the eyes to contract. The chart [PDF] shows Sam's absent ocular and cervical VEMP responses (top) in comparison to normal cervical and ocular VEMP responses (bottom).
Cervical VEMPs can be measured in newborns, but ocular VEMPs are typically not present until at least 12 months of age. One of the biggest issues in cervical VEMP testing with young kids is maintaining sustained muscle contraction. General reinforcement and coaching is sufficient for many children, otherwise toys or fun computer animations can be used to help sustain head turning. With ocular VEMP, for which children need to sustain an upward gaze, older children can lie in a semi-recumbent position and view fun stickers on the ceiling. Due to the high sound levels used for VEMPs, many clinicians have expressed concern about safe sound levels for children's ears. We are working on a study to determine safe presentation levels for the pediatric population.
Video head impulse test. The vHIT, an assessment of the horizontal, superior and posterior semicircular canals, is new on the vestibular testing scene. The vHIT is exceptionally helpful in assessing children for the same reasons as VEMP: vHIT provides ear-specific—even canal-specific—information, is quick to administer and does not cause dizziness. Complete the vHIT by having the patient—child or adult—sit approximately one meter from a visual target on the wall. While the patient watches the visual target, the examiner stands behind the patient and performs brief, abrupt and unpredictable head impulses in the plane of each semicircular canal. The vHIT goggles measure eye and head velocity, providing information about the function of each semicircular canal.
At Boys Town, we have had excellent success completing vHIT with children older than 6. When testing children, we provide frequent breaks to eliminate fatigue, and we put children's stickers—super heroes, princesses and so forth—on the wall as visual targets. To ensure children maintain gaze on the target, we ask questions about characters on the stickers (for example, "What color is Superman's cape?") while performing head impulses.
Rotary chair. Rotary chair is the only assessment of semi-circular canal function available for children, specifically infants. The child sits in a motorized chair, which is rotated at various computer-controlled frequencies. One of the downsides of rotary chair is that it does not provide ear-specific information.
Most children tolerate rotary chair fairly well, especially if they are put at ease by singing songs. We sometimes ask children to count or recite nursery rhymes. A car seat can be placed in the rotary chair for small children to ride by themselves, but generally children are seated on a parent or practitioner's lap. At Boys Town, 6 months is the youngest age we complete rotary chair testing on children.
Videonystagmography. Most clinicians are familiar with VNG testing. We have found that full VNG testing, including ocular motor, positional and caloric testing, can be completed on children as young as 5, depending on the child's willingness.
Who needs vestibular testing?
Although we don't yet understand fully the functional consequences of vestibular loss in children, vestibular assessment should be considered for high-risk children—those who obtain a cochlear implant, have a hearing loss etiology known to be associated with vestibular loss (CMV, meningitis, etc.), or have hearing loss with complaint of gross motor developmental delay. Like adults, children can develop vestibular disorders—such as vestibular neuritis or migraine variant—unrelated to hearing loss. Therefore, vestibular assessment should also be considered whenever a vestibular disorder is suspected.
In addition to asking parents questions about their children's gross-motor milestones, rotary chair continues to be the assessment of choice for children younger than 4 or 5. For older children, experts recommend cervical and ocular VEMPs along with some assessment of canal function—such as rotary chair, vHIT or caloric testing—to provide information about canals and otolith organs. Be sure to consider age-appropriate normative data when assessing children, because vestibular function can vary as a child grows.
Following a diagnosis of vestibular loss, audiologists should consider habilitation to address vestibular-related symptoms. Children with significant vestibular loss or who have a history of developmental delay are recommended for—at minimum—a vestibular rehabilitation consultation.
Continued research is needed to establish criteria for both assessment and rehabilitation. Most important, for children like Sam who have both hearing and vestibular loss since birth, research is needed to understand the developmental consequences of vestibular loss—and to better understand the extent to which these consequences can be remediated.