Influence of a vestibular dysfunction on the motor development of hearing impaired children

Hearing impaired children have a higher risk for motor deficits and more specifically balance deficits. Since balance control requires integration of visual, somatosensory, and vestibular information by the central nervous system to generate motor responses that keep the body in balance, the balance problems of hearing impaired children might not be surprising. The vestibule and the cochlea are closely related both anatomically and developmentally. Consequently, it is reasonable to presume that many hearing impaired children have concomitant vestibular loss. However, all mechanisms causing poor balance are not yet investigated systematically in auditory impaired children. The main objective of this thesis was to identify the predictive ability of vestibular function test results as well as other factors like the degree of the hearing loss, the etiology of the hearing loss, a cochlear implantation, and additional disabilities on the motor performance in hearing impaired children. Beforehand, the usefulness of different assessment tools to evaluate postural stability in children needed to be investigated. This aim was achieved through different studies: reliability and validity of posturography and clinical balance tests in children between 6 and 12 years, usefulness of the norm reference values of the Alberta Infant Motor Scales (AIMS) in Flemish infants between 0 and 18 months, and reliability and validity of the Ghent Developmental Balance Test (GDBT) in children between 18 months and 5 years. Reliable information regarding postural stability of typically developing children and hearing impaired children between 6 and 12 years may be obtained utilizing posturography and clinical balance tests. From different COP (Center of Pressure) stability parameters, sway velocity is the most reliable parameter. The standard deviation (SD) of sway velocity, sway area, SD of anterior–posterior and SD of medio-lateral COP data showed moderate to excellent reliability but some caution must be taken into account in some conditions, like in bipedal standing with eyes open. Clinical balance tests have proven to be as reliable as the sway velocity of posturography. Correlations among the different balance assessment tools were low, confirming that posturography and clinical balance tests are two different constructs in the assessment of balance control. They provide different but complementary information. Therefore, an assessment protocol for balance consisting posturography as well as clinical balance tasks is proposed. Balance cannot be evaluated by a single test and it can only be interpreted in relation to different tests used in an assessment. New reference values are needed for the AIMS, an assessment tool to examine the gross motor movement repertoire in infancy, for accurate identification of infants at risk for motor developmental delay. The lower motor scores seen in Flemish infants seems to be related to the sleep position, the amount of play time in prone, in supine, and in a sitting device. Tummy time in a supervised environment and variation in play positioning must be advocated to optimize early motor milestone acquisition. The GDBT is a new assessment tool for the evaluation of balance in toddlers and preschool children. The GDBT appears to be a promising outcome measurement tool to screen for balance difficulties and to plan intervention programs aimed at improving balance. Test-retest and inter-rater reliability of the GDBT is excellent. Correlations between the GDBT and balance subscales of other motor assessment tools are moderate to high while correlations with subscales measuring constructs other than balance are low, confirming the construct validity of the GDBT. Hearing impaired children are at risk for balance deficits. The balance deficits can be predicted by vestibular function test results, rotatory chair and Vestibular Evoked Myogenic Potential (VEMP) testing, as well as by the etiology of the hearing impairment. Presence of a VEMP response is an important clinical parameter because comparison of motor performance among hearing impaired children between those with present and absent VEMPs showed significant differences in balance performance. The three most important predictor variables on motor performance by bivariate regression analyses are the vestibular–ocular reflex (VOR) gain value of the rotatory chair test at 0.01 and 0.05 Hz frequency, as well as the VEMP asymmetry ratio. Multivariate regression analyses suggest that the VOR asymmetry value of the rotatory chair test at 0.05 Hz and the etiology of the hearing loss seem to have additional predictive value. It can be concluded that balance deficits in hearing impaired children are strongly associated with the function of the vestibular apparatus and that reliable and valid test protocols are available to evaluate the balance performance in children. Those test protocols are important for future research about the influence of a cochlear implantation on the motor performance of hearing impaired children