Just as early identification of hearing loss has gained prominence within our profession, the early identification of vestibular disorders is also an important topic of discussion. It makes sense that the vestibular system may also have been affected by a pathology that has affected the cochlea. As one delves into this professional body of literature, although it appears sparse, he/she sees that vestibular disorder may occur co-morbidly with a number of hearing disorders. Similarly, it may be evident in the presence of normal hearing sensitivity.
The audiology profession has exploded with new technology, including in the area of vestibular assessment with patients of all ages. Clinical services have greatly progressed since the days of viewing post-rotatory nystagmus through Frenzel lenses. While one of the gold standards of care still appears to be Videooculography (VOG) in many clinics, the audiologist also may add the following diagnostic measures to the evaluative battery: Rotary Chair (RC), Computerized Dynamic Posturography (CDP) and Vestibular Evoked Myogenic Potentials (VEMPs). Of course, these important sections of a vestibular evaluation battery are also performed within a larger framework including comprehensive audiologic evaluations, other electrophysiologic measures, and thorough otolaryngologic examination, imaging, and methods.
Audiologists with vestibular-related practices have come to realize the limitations that arise upon performing VOG with young children. Traditionally, electrodes have been used (via electrooculography or EOG), resulting in great challenges to keep them in place. Goggles and the accompanying infrared camera utilized for a more updated examination via VOG may also present difficulty in acceptance of the head gear by the pediatric patient. In progressing through the entire VOG battery, the creative examiner has also sought novel ways to attain valid results during head and body maneuvering and especially during bithermal caloric irrigation.
As the above-mentioned newer evaluative measures came into play, audiologists began to consider whether these measures may be more appropriate than VOG for use with younger children. There are two major premises that must be highlighted, when considering vestibular evaluation with pediatric patients. The first is that creativity must be exerted in adapting adult techniques for pediatric use. Secondly, pediatric normative data must be gathered, so that diagnostic results obtained in the clinic with children are not compared to adult normative data.
Review of Literature
Maturational effects of per-rotatory responses in children were especially studied in the 1970s (Eviatar, Eviatar, & Naray, 1974;Eviatar, Miranda, Eviatar, Freeman, & Borkowski, 1978). Although full-term infants demonstrate a stronger nystagmic response than premature cohorts, the responses appear to be comparable by nine months of age. Effects of age upon the vestibular-ocular reflex (VOR) following caloric irrigation has also been studied by numerous researchers with varying results. Van der Laan and Oosterveld (1974) found less intense nystagmic beat frequency and higher amplitudes with children, as compared with adults. Krejcova and colleagues (1975), however, reported that children demonstrate a higher frequency of beats than adults. Andrieu-Guitrancourt et al. (1981) discovered that frequency of beats increases as a child matures, while maximum eye speed diminishes. Amplitude and eye velocity measures have been found to be stronger in infants versus adolescents in some studies (Ornitz, et al., 1979) while other researchers noted more intense response in adulthood (Mulch & Peterman, 1979). The VOR goes through several developmental stages in infancy (Donat, Donat, & Swe Lay, 1980) and it should be considered abnormal if the VOR is absent by the age of ten months of age (Fife, et al., 2000). The examiners referenced have stressed the importance of considering these age differences when interpreting pediatric test results (Kenyon, 1988;Levens, 1988).
As one peruses the literature related to pediatric vestibular evaluation, several bodies of literature are apparent with little overlap. The first body has been contributed by Occupational (OT) and Physical Therapy (PT) colleagues, suggesting that vestibular disorders may co-exist with such entities as dyslexia, motor delay, autism, learning disability and others. Upon collaboration with OT and PT colleagues, one learns about diagnostic measures that are very different than those utilized within audiology and otolaryngology communities. Regarding treatment, clinicians hear such terms as "vestibular stimulation" and "sensory integration" that are not household terms within the audiology profession. The second body of literature has been provided by audiology and otolaryngology colleagues;although not an abundant body, co-morbidity been described between vestibular disorders and etiologies such as sensorineural hearing loss, otitis media, benign vertigo of childhood, numerous childhood syndromes and others.
Diagnostic Measures for Use with Children
Rotary Chair (RC)
Cyr and colleagues (1980, 1983) were at the forefront in stressing the importance of vestibular evaluation in children, adapting adult techniques for pediatric use, and reminding the profession that many children may and should be evaluated. Their RC enclosure was painted to resemble an inviting spaceship and they sat children as young as three months of age upon parental laps. They filled the visual field with cartoon characters for optokinetic testing, while the characters served additional roles in calibration, pursuit, and other oculomotor tests. These examiners piped familiar children's songs into the "spaceship" for tasking purposes and adapted an infrared camera for observation of the VOR. While only a screening could be adapted for this population (.08 Hz), as opposed to implementing all RC subtests, much valuable information was gained. While the testing techniques were quick and efficient, one of the major obstacles to overcome was keeping the electrodes intact and properly placed!
Staller et al. (1986) also described RC testing with children, although these investigators tested frequencies from .01 to 16 Hz. While nystagmus could not be observed in response to rotation at .01 Hz in very young children, it could be elicited by the age of ten months. The authors felt that phase differences found in subjects younger than four years were an indication that the VOR was still developing at this age. Valente (2007) performed RC testing at .08 Hz and .5 Hz with a group of preschool children and a group of pre-adolescent children. No significant age effects were seen with regard to gain, phase or symmetry measures. When pediatric results were compared with adult normative data, however, both groups of children demonstrated a significantly higher gain measure at .08 Hz. All children also demonstrated a significant phase lead at .08 Hz when compared to adult normative data. The author also performed Step Velocity subtests, where time constants were measured for both clockwise (CW) and counterclockwise (CCW) conditions. Measured time constants are defined as the time (in seconds) it takes for pre-rotary and post-rotary nystagmus to diminish to 37% of its original strength. Improved head stabilization methods may be recommended so that more reliable measures may be attained with children.
Adaptation of adult RC techniques for children is extremely important, and a decorative enclosure is especially inviting. While many children consider RC to be ridelike and may be tested without benefit of a parent lap, the examiner should bear in mind that the environment is darkened. Continual interaction, reassurance and positive reinforcement are crucial. Many children adapt well to pediatric-sized goggles and older children are comfortable with the adult size. Even though gain, phase, and symmetry measures appear to be reliable with children, it is important to also view and record the VOR via infrared camera and television screen. In view of limited attention span, the audiologist may wish to vary the protocol with regard to frequencies tested, in the event that all frequencies may not be performed.
Computerized Dynamic Posturography (CDP)
The Sensory Organization Test (SOT) subtest of Computerized Dynamic Posturography (CDP) has also been studied with children. The reader may recall that this is considered to be a test of functional balance that measures relative contributions of visual, proprioceptive and vestibular systems. There are six conditions, with the first being a baseline where the visual surround and platform are stable. Conditions become increasingly more difficult such that the subject maintains balance with use of vestibular cues alone during the fifth and sixth conditions. Di Fabio and Foudriat (1996) reported that a child as young as three years of age may be efficiently tested with CDP techniques. Hirabayashi and Iwasaki (1995) reported that somatosensory function reaches adult maturational levels by the age of three or four years. The visual system develops to adult acuity by fifteen years of age while the vestibular system is the last to develop. Shimizu et al. (1994) found that pediatric scores on SOT subtests differed significantly from adult scores in many conditions. Males' scores continued to improve after seven years while scores of female subjects remained relatively stable. Rine et al. (2000) conducted CDP studies with three to seven year old children, finding that this test provides useful information related to the sensory systems and their maturation. Cyr et al. (1988) studied CDP in addition to RC, advising that CDP be used with children when the following conditions exist: history of imbalance, clumsiness according to parental report, neurological involvement, and suspected organic disease.
Valente (2007) studied the SOT and the Motor Control Test (MCT) with the same two groups of children described above and compared pediatric results with adult normative data. Significantly poorer performance was seen on all six SOT conditions when scores of younger, pre-school aged children were compared with those of older, pre-adolescent children. Similarly, significantly diminished scores were seen on all conditions when pediatric findings of both age groups were compared with adult normative data. These findings underscore the importance of studying maturational effects and of comparing pediatric results with pediatric normative data. With the MCT, the child is secured with feet on the platform and the platform undergoes unexpected, random forward and backward translations. Translations are of small, medium and large magnitudes with a latency measure in milliseconds calculated. This latency represents the time it takes from the beginning of platform movement to the time pressure is exerted by the feet to maintain balance. Extent of translation is dependent upon height of the subject and, at the time the study was conducted, equipment manufacturer recommendations were that the child weigh at least 40 pounds for optimally reliable research measures. Valente (2007) adapted MCT techniques and found that the latency measure could also efficiently be attained with children and contributed to pediatric normative data banks for this subtest.
Adaptations for children include utilization of the smallest harness and implementing an interesting, child-like visual surround. With SOT, reliability is improved with performance of three trials of each condition. During the 20 seconds of each trial, continual positive reinforcement is essential. Children oftentimes also feel that this measure is "ride-like" and it reassures them to know they cannot fall and that a parent is not far away.
Vestibular Evoked Myogenic Potentials (VEMP)
Vestibular evoked myogenic potentials (VEMPs) have gained clinical utility with adults over recent years, adding an important measure of otolith function to the test battery. Colebatch and Halmagyi (1992) described a procedure for recording the VEMP from the sternocleidomastoid (SCM). Many research studies followed that described test protocols and findings displayed when a patient exhibits various disorders. The authors demonstrated that this response is most likely saccular in origin, noting that VEMP has been effectively recorded in the presence of profound sensorineural hearing loss (Colebatch & Halmagyi, 1992;Halmagyi & Colebatch, 1995). Important parameters measured and utilized by the clinician for interpretation include waveform latencies, amplitude, morphology and threshold measures. The time-efficient, objective and non-invasive nature of VEMP has facilitated its utilization with the pediatric population.
Sheykholeslami, Megerian, Arnold, and Kaga (2005) successfully attained VEMP tracings with typically developing neonates and with a group demonstrating clinical findings. Wave morphology was found to be similar to that of adults, although latencies appeared shorter and amplitudes were more variable than those observed with adults. Kelsch and colleagues (2006) recorded the VEMP in children from 3-11 years of age, also finding shorter latencies than in adults. They concluded that this is a well-tolerated measure for screening vestibular function in children. Valente (2007) successfully performed VEMP testing with groups of preschool and preadolescent children, following procedures thoroughly described by Akin and Murnane (2000). Stimuli used to obtain recordings were 500 Hz tonebursts and clicks. The most robust waveforms were elicited via the 500 Hz stimulus, and normalized amplitude measures were calculated. No age effects were seen with P1 or N1 waveform latencies between the two groups of children, although both groups demonstrated significantly shorter latencies when compared to adult normative data. Among other recommendations were that methods be developed to monitor and standardize the level of neck contraction in children, since this may introduce variability into interpretation of P1-N1 amplitude measures. This area has been studied in adults, with application of additional electrodes and computer software to monitor EMG activity levels (Akin & Murnane, 2000). It may be helpful to have a child seated on a parent lap for performance of VEMP. Additionally, simultaneous, bilateral recordings may be more effective with children than traditional unilateral adult recordings.
Additional Components of the Evaluative Battery
The above measures, effectively utilized with children, may be considered portions of an overall evaluative battery, with the audiologist serving as one important team member. Other important aspects of the diagnostic session may include a thorough history, audiologic evaluation, neuro-otologic evaluation, physical examination, visual examination, and others. The clinician should not overlook Video-oculography (VOG) as a useful tool, whenever it may be implemented. Development of an efficient vestibular evaluation battery must also consider adaptations for special needs and at-risk children. In addition to the samples of hearing children described above and to help address the issue of adaptation for special-needs children, Valente (2007) also recruited a sample of hearing-impaired children. These children ranged in age from pre-school to pre-adolescence, and it was found that RC, CDP and VEMP could efficiently be performed with modifications. The following paragraphs outline two very interesting case studies where the battery was performed with hearing-impaired children. Although younger subjects were recruited, the two case studies highlighted below are nine-year-old friends who came to the clinic together and who demonstrated very different results.
Case Studies with Hearing Impaired Children
Case #1
Subject #1's mother accompanied him to the evaluation and reported that the etiology of his hearing loss is unknown, as is acquired versus congenital status. Audiologic evaluation revealed a profound, sensorineural hearing loss bilaterally, with the right ear slightly better than the left in lower frequencies. The child wears a cochlear implant in the left ear. RC testing was performed easily at .08 Hz and .5 Hz, revealing normal gain, symmetry and phase measures. Step Velocity testing also revealed time constants within normal limits in response to both clockwise and counterclockwise rotations. Robust nystagmic activity was noted with each frequency tested. Special adaptations with hearing-impaired children were to make certain all instructions were provided in a well-lit environment with integration of both auditory and visual cues. This is especially important, since the talk-back system may not efficiently be utilized when the child is seated within the darkened enclosure. Tasking may be accomplished via traditional means with children who utilize oral communication, making certain that they take an active role. Although case studies highlighted here do not use total communication, past studies have effectively tasked children as they signed familiar songs or stories (Brookhouser, Cyr, & Beauchaine, 1982).
With the SOT subtest of CDP, results were unremarkable until a fall was noted with Condition #4, where the platform was sway-referenced and eyes were open. Performance tended to improve with subsequent trials of this condition and this possible practice effect carried over to Condition #5. Significantly lowered scores were seen for Condition #6, when the platform and visual surround were sway-referenced. These results are indicative of functional balance difficulty when visual and proprioceptive cues are compromised. Latencies obtained on all trials of the MCT were unremarkable and appeared grossly within normal limits.
VEMP latencies and amplitudes were obtained for both click and 500 Hz toneburst stimuli. VEMP tracings were present, and all measures for both the right and left ears appeared to be consistent with those obtained for normal-hearing cohorts. In summary, this child appeared to exhibit essentially normal vestibular function, at least with regard to RC and VEMP. He appeared confident and sure of his surroundings during the session, even when visual cues were removed. As previously described, CDP revealed some functional difficulty particularly when the system was taxed. Information gained from this case study includes verification that techniques may be utilized with hearing-impaired children with little modification. Hearing-impaired children may demonstrate normal or near-normal vestibular findings on many subtests, with more subtle difficulties on others, as well as normal VEMP tracings as in this case.
Case #2
Subject #2's mother also accompanied him to the evaluation and reported that the hearing loss is a result of suffering from meningitis at the age of two years. Audiologic evaluation revealed a profound, sensorineural hearing loss bilaterally, with the left ear slightly better than the right in lower frequencies. The child wears a cochlear implant in the left ear. RC testing was performed easily at .08 Hz and .5 Hz, revealing immeasurably low gain measures at .08 Hz. Because the gain measure was so low, accurate calculations/interpretations could not be ascertained regarding phase and asymmetry measures. No nystagmic activity could be observed in response to chair rotation. When RC testing was performed at a higher frequency of .5 Hz, however, borderline normal/hypoactive gain and borderline asymmetry measures were observed with a questionably abnormal phase measure. Although nystagmic activity could not be observed via camera at this frequency, test results do indicate presence of some vestibular function. Step Velocity testing also revealed hypoactivity to both clockwise and counterclockwise rotations, resulting in inability to measure time constants. No nystagmic activity was noted in either direction during this subtest. The child easily adapted to testing techniques, including wearing of goggles, tasking, and tolerance of the darkened enclosure.
With the SOT subtest of CDP, results were essentially unremarkable with practice effects seen across trials until significantly reduced scores were noted with Condition #4, when the platform was sway-referenced and eyes were open. Significantly lowered scores and falls were seen for Conditions #5 (eyes closed and platform sway-referenced) and #6 (platform and visual surround sway-referenced). These results are indicative of severe functional balance difficulty when the child relied upon vestibular cues alone. Some latencies obtained following trials of the MCT were slightly prolonged and it appeared that better performance was seen with forward, as opposed to backward, translations.
VEMP latencies and amplitudes were obtained for both click and 500 Hz toneburst stimuli. No VEMP tracing could be attained for the right ear, in response to the 500 Hz stimulus. VEMP tracings were present for other stimuli, and measures for both the right and left ears appeared to be consistent with those obtained for normal-hearing cohorts. In summary, this child appeared to exhibit significant vestibular function concomitant with his profound, sensorineural hearing loss. He appeared unsure of his surroundings and disoriented when visual cues were removed and his mother corroborated these behaviors at home. Abnormal findings were seen with several RC and CDP subtests, with actual falls noted upon vestibular system reliance. A VEMP tracing was absent for the right ear, with stimulation at 500 Hz.
Conclusions
The area of pediatric vestibular evaluation is a highly interesting one, where additional clinical work and research are needed. It is important to further study vestibular disorders and aspects of their co-morbidity with a myriad of other disorders. Many clinicians feel that a vestibular case history is one of the most valuable tools utilized with a patient of any age who demonstrates a vestibular disorder. More efficient and cost-effective case history protocols and screening tools should be developed for pediatric patients, in addition to a greater degree of collaboration among disciplines. It is important to carefully consider input from all team members and all components of the diagnostic battery, as clinicians modify adult evaluative techniques for use with children. More research is needed regarding optimum test battery reliability and validity, as well as evaluative tools and subtests that have not yet been studied. As procedures are developed, it is also crucial to collect pediatric normative data so that pediatric results are not compared to adult normative data and so that misinterpretation does not take place. Testing techniques may be modified for hearing-impaired and other at-risk children who may demonstrate a high incidence of abnormal vestibular findings. Many should be tested as early as possible. With regard to treatment, it is important to gather evidence, apply best-practice toward management of the child and his/her vestibular disorder, and employ a team approach as with evaluation. Clinicians should not assume that maturation or compensation will automatically preclude the need for treatment. As with hearing loss, clinicians must seek ways to identify at earlier ages and to initiate early intervention when and if warranted.
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