Chapter 3 Assessments of Vestibular Functions

Transcription

1 Chapter 3 This chapter describes methods for assessments of vestibular function by clinical methods under two sections. The first part of assessments relies on neurophysiological mechanism and the second section is based on sensory integration model. Under Sensory Integrative model, the vestibular-system is assessed for its efficiency in modulating the sensory information for the end-product of praxic abilities. It concludes with discussion on other alternative standardized assessment tools for interpreting vestibular dysfunctions Assessment Based on Neurophysiological Mechanisms The integrity of the vestibular system is assessed by testing the functions mediated through: I. Vestibular-spinal mechanism and II. Vestibular ocular mechanism. For a comprehensive interpretation of the vestibular system researcher recommend assessment of both mechanisms Vestibulo-spinal Tests: It includes static and dynamic conditions to evaluate the peripheral vestibular functions by a series of tests assessing balance or postural reactions. Montgomery (1985) provides a comprehensive review of test used to measure vestibular function. A brief overview of tests are provided below to help understand the historical importance vestibular system has received and to appreciate the complexity of test performance and interpretation of the results. i) Postural Control Test: Therapist primarily relies on postural tests to assess vestibular system integrity. Postural test primarily assess balance on a series of position or tasks (Fife et al., 2000). Postural control is not very specific for vestibular dysfunction, because, of complex interaction from other sensory systems (visual, somatic, and proprioceptive) on postural control (Montgomery, 1985). The clinical tests can be classified as static and dynamic postural tests. Static postural tests used with children are Romberg - or standing with eyes closed. However, its clinical utility is limited because children with intact proprioceptive system can compensate well despite vestibular deficits. Standing with heel-to-toe position with eyes closed, arms folded across chest (sharpened Romberg) is a more demanding measure of balance and can discriminate children with or without vestibular deficits. P a g e 25

2 Dynamic postural tests provide valid results on vestibular dysfunctions. These include a range of tests such as: tandem walking; walk on floor eyes closed, changing-consistency board and past-pointing test. The past pointing test involves, subject with eyes closed raises arms with extended finger and then returns to the examiner's finger. The arm that deviates represent ipsilateral vestibular deficit (Montgomery, 1985). Cunningham and Goetzinger (1972) reported normative data for tandem walking in children from 8-18 years. Tandem gait test is included as the routine neurological examination for posture and balance dysfunctions. When performed with eyes open, tandem walking is primarily a test of cerebellar function. Falls in the tandem gait test, eyes closed, are indicative of peripheral vestibular dysfunction (Ronthal, 2002). However, some healthy subjects are unable to succeed in this test and thus, the test results are non-specific (Baloh & Hornubia, 2001). Nyabenda et al. (2004) observed clinical postural tests lack normative information especially for children and subsequently developed norms for the vestibulospinal (Romberg test, Unterberger-Fukuda and Babinski- Weil tests; gait testing eyes closed for a 5-m distance) and rotational tests in young and older adults of 20 to 70 years. Other evaluations involve use of technology such as force platforms and computer based analyses of data consisting of weight, pressure and center of gravity Vestibular-Ocular Reflex (VOR): VOR is reliable indicator of vestibular function. It is mediated by mechanism of semicircular canals and its connections to ocular nucleus. The labyrinth impulses through vestibular nuclei relay to cranial nerve nuclei III (Oculomotor), IV (Trochlear), and VI (Abducens). It helps to stabilize image on retina while head is rotated or as body move linearly. It is elicited by subjecting the body to rotate/spin for a short while and bringing to sudden halt. This maneuver, induces nystagmus - an involuntary oscillation of eyes, characterized by alternating slow and fast (rapid) ocular movements. By convention, the nystagmus is named by the direction of the fast component. This phenomenon is referred to as Vestibular-Ocular reflex (VOR) and is generally limited to responses from the horizontal semicircular canals. The function of the vertical semicircular canals and the utricle and saccule are not tested by commercially available vestibular testing equipment. Nystagmus has been demonstrated in newborn infants as early as days of life through caloric stimulation (Eviatar et al., 1974), and by rotatory stimulation (Ornitz et al., 1979). VOR responses normalize by 2 months of age and mature further in the first 2 year of P a g e 26

3 life. Sometimes responses are not obtained in premature neonates and in those less than 6 months old (Eviatar & Eviatar, 1979). VOR is interpreted with respect to duration, frequency, short phase and long phase. The normative data indicates the nystagmus parameters to decrease with increasing age. On contrary the frequency of nystagmus increased from 2 years through ten years in old children but maximum eye speed in the slow phase decreased (Ornitz et al., 1979). Among these parameters, the duration is the preferred measure of choice with examiner using manual or direct observation method. Ayres (1978) measured duration of nystagmus (popularly known as post rotatory nystagmus test - PRNT) to differentiate vestibular dysfunction in children with learning disability. Scores less than 1SD (standard deviation) below mean was indicative of abnormality. However, other researchers have cautioned against use of duration of nystagmus as an indicator of vestibular function. It is reported that duration of nystagmus varied little with increase in rotatory stimuli indicating duration is more or less constant for each individual. However, later research indicated that increased duration of PRN is a result of decreased inhibitory influences of cortical centers (Markham, 1972). Kantner et al. (1976) postulated that increased duration indicated vestibular hyper-reactivity resulting from failure in maturation of an inhibitory circuit in the central nervous system. Other researchers postulate, speed of the slow phase of nystagmus and frequency of nystagmus beat to be better indicator of vestibular integrity (Montgomery, 1985). VOR is influenced by many central nervous system mechanisms (which act as inhibitory and excitatory), sate of arousal and on environment as well. Thus, it is not a sensitive measure of vestibular mechanism (Tibbling, 1969) and children in both normal and with learning disability showed large variation on PRNT (Ayres, 1976) Assessments of Vestibular Dysfunction Based On Sensory Integration Model Two approaches are followed for assessment of sensory integration dysfunction for vestibular system: i) Modulation of sensory input by studying the behavioral or responsivity pattern to vestibular stimuli and ii) Analyzing the motor output of vestibular integration. Sensory integration and praxis test (SIPT) is one such tool developed by Ayres (1989) to assess praxis as the end-product of sensory integration with emphasis on vestibularproprioceptive processing. These assessments are further supplemented with evaluation of P a g e 27

4 vestibular function and includes assessment based on clinical observations of posture/muscle tone, equilibrium reactions and strength and standardized motor proficiency tests such as Bruninks-Oseretsky Test of Motor Performance (BOTMP) (Bruininks, 1978), Movement Assessment Battery for Children (MABC) (Henderson & Sugden, 1992) Assessment of Sensory Modulation: In these methods, the responsivity pattern of children to various sensory experiences are obtained through interview with parents/teachers. Therapists rely on non-standardized inventories, questionnaires or on direct observation. Sensory profile is one such tool developed by Dunn (1994) to determine sensory processing abilities of children in every- day activities rated by parents on frequency of behavior on 5 point scale. Daniels and Dunn (2000), Dunn (1994), Dunn and Westman (1997), Parush et al. (1994), reported sensory responsivity to tactile system across age and gender. Other questionnaires and inventories used by occupational therapist are sensory history questionnaire (Larson, 1982) and Touch Inventory for Elementary-School-Aged Children (Royeen, 1986); Touch Inventory for Preschoolers (Royeen, 1985, 1987); Sensory Rating Scale (SRS) (Provost & Oetter, 1993). Parush et al. (1994) reported tactile responsivity in typical children to differ among gender of 1 ½ 2 ½ years. Developmental trend in sensory responsivity was reported to differ in children with abnormal neurological involvement (Daniels & Dunn, 2000). Wartling et al. (2001) recommends study of the typical responsivity behavior pattern for various sensory systems, in typical children across age and gender. Bar- Shalita et al. (2005) reported no difference in the vestibular and tactile responsivity patterns in 3 and 4 years Israel children for hypo- and hyper-responsivity behaviors Assessment of Functional Support Capabilities (Kimball, 1999): i) Clinical Observations of Postural Movements: To substantiate findings from standardized tests, a set of clinical observations is recommended (Ayres, 1989). These items are believed to closely related with tests of cerebellar-vestibular function (Wilson et al., 1992), and reflect soft neurological signs (Short et al., 1983; Wilson et al., 1992). The original protocol included 19 items: examination of muscle tone, postural control, reflex integration (asymmetrical tonic neck reflex-atnr) and rapid alternation movements of the hands, prone extension pattern against gravity, elicitation of righting and equilibrium responses (DeGangi et al., 1980). A 3- point scale P a g e 28

5 rating scale was proposed, however, administration was not standardized. Dunn (1981) brought standardization in administration and scoring for the observations. Ottenebacher (1978) adopted 3 point scale, with higher scores indicating normal. Holding the prone extension and supine flexion for 20 seconds was considered desirable. Harris (1981) scored on the quality of posture held for each body segment on 2-point scale. Cluster of postural-ocular movement disorders was proposed to indicate vestibular-proprioceptive dysfunction (Fisher, 1991). The following six subtests constitute the clinical observations suggestive of poor postural-ocular movement disorder: a. Prone extension. b. Supine flexion c. Muscle tone (Extensor) d. Proximal joint stability (or muscle co-contraction) e. Postural adjustments f. Equilibrium and g. Post rotatory nystagmus (PRN) Prone extension is ability to hold hyper extended posture with legs and arms abducted, elbow flexed and head held above supporting surface. Supine flexion is to hold posture with arms crossed on chest, ankles crossed, and neck, hips, and knees flexed ( roll up in a ball ). Both positions were scored for holding posture up to 20 seconds duration. Sellers (1988) used a four point scale for measuring the quality of posture for both tests. Muscle cocontraction is observed for ability to hold rigid posture of body segments by simultaneous contraction of antagonistic muscle groups while examiner applied alternating resistance (Ottenbacher, 1978); Muscle tone is evaluated by passively extending joints of upper extremities. The muscle tone, is attributed to vestibular function. Researchers, evaluated muscle tone by checking the hyper- extensibility at elbow, but is reported as not suitable for clinical assessment (Short et al., 1983). It is hypothesized, maintaining prone extension posture depends on adequate processing of gravity information via vestibular nuclei and lateral vestibulo-spinal tract to extensor motor neurons. Short et al. (1983) established norms on 156 pre-school children. Gregory-Flock and Yerxa (1984) provided normative data on 242 normal children from 4 8 P a g e 29

6 years for duration and quality of prone extension test. The duration of holding the posture varied in different studies. Bundy and Fisher (1981) and Short et al. (1983) considered 20 seconds duration for holding static posture. On the other hand, Gregory-Flock and Yerxa (1984); Harris (1981); Wilson et al. (2000) observed that six years old children were able to maintain posture for 30 seconds. In general, it indicates that maturity in vestibular nuclei mediated motor tracts by 6 years of age. Younger children demonstrated variable performance. Parvatikar and Vaidhya (2010) reported that Indian children of 5-8 years could hold the prone extension posture for an average duration of 15 seconds with marginally longer duration for the 5 years older than the 8 years. Clinical methods of assessment are reported to correlate with low PRN scores (Ottenbacher et al., 1981), however, Bundy and Fisher (1981) did not find correlation of prone extension with the PRN scores, which are indicative of vestibular impairment. Sellers (1988) observed supine flexion performance was significantly related to static and dynamic balance performance, whereas prone extension performance was related only to the quality of dynamic balance performance. Assessment of equilibrium reflects vestibular and proprioceptive function (Bundy, 2002). Righting and equilibrium responses are elicited by tilting child in space laterally or assuming position on unstable surface (Montgomery, 1985). Fisher (1989) developed objective tests of quality of equilibrium on tilt board and flat board in school children. They reported qualitative difference in response to tilt board by children with learning disability when compared with normal children in clinical set up. The difference reported were that children with vestibular dysfunction used primitive strategy more often than their typical counterparts. Post rotary nystagmus considered the best indicative of vestibular system is tested (Mulligan, 2011) with child seated on rotating platform with neck flexed forward to 30 degrees (to stimulate the horizontal semicircular canals). Therapist rotates the platform for 20 seconds, following which duration of nystagmus is observed. According to Ayres (1978) hypoactive or hyperactive nystagmus is indicative of vestibular dysfunction. Cohen (1989) and Polatajko (1983) questioned the validity of results interpretation, as it involves testing with eyes open. Further, testing of oculomotor function by occupational therapists is controversial within the field of pediatrics (Wilson et al., 1992). Therefore, therapist often P a g e 30

7 depended on other clinical methods discussed above and in this thesis, PRN is not covered or used as screening tool to identify children with vestibular dysfunctions Assessment End Product Abilities (Kimball, 1999): i) Praxis: Ayres (1979) hypothesized that efficient sensory integration, is foundation for ability to plan and execute movement. The praxic ability enables to interact with environment and learning. Sensory Integration and Praxis Test (SIPT) developed by Ayres (1989) evaluates processing deficits related to visual, tactile, vestibular and kinesthetic sensation as well as motor performance. It is modified from the earlier version of Southern California Sensory Integration Test (SCSIT) (Ayres, 1980) and Post-rotary nystagmus test (PRNT) (Ayres, 1975). SIPT consists of 17 brief tests. Although, role of vestibular and proprioceptive systems in the process of sensory integration is highly emphasized, the SIPT contain only three measures of vestibular or proprioceptive functions: a. Post rotatory nystagmus (PRN) test, b. Standing and Walking balance and c. Kinesthesia. Mulligan (1998) concluded from a factor analytic study that these three items to be a weak measure. Therefore, it is recommended to supplement SIPT with clinical observations of neuro-motor performance (CONP) (Fisher, 1991). ii) Bilateral Motor Coordination: It includes observation of age-appropriate hopping, skipping, and jumping with both feet together. Magalhaes et al. (1989) studied the development of jumping jacks, symmetrical jump and reciprocal jumping in children and reported jumping jacks was attained by 7 years. The jumping tasks is hypothesized to depend on praxis abilities and was reported as suitable for screening praxic abilities in children (Magalhaes et al., 1989). Subtest of the Bruininks-Ostersky Test of Motor Proficiency (BOTMP) consists of bilateral integration (Bruininks, 1978) on non-habitual motor tasks as well. To get a comprehensive assessment of vestibular functions in children the clinical tests are combined with standardized tests such as SIPT or BOTMP Other Standardized Assessment Tools Various test of standing balance (with eyes open and eyes closed); and of tandem walking which are parts of larger test batteries such as BOTMP, Pediatric Balance scale are P a g e 31

8 used as alternative tests to indicate vestibular function. Selected items on standardized tests, such as Movement Assessment Battery for Children (MABC) (Henderson & Sugden, 1992), Miller Assessment for Pre-schoolers (MAP) (Miller, 1988) are also used by practioners (Kinnealey & Miller, 1993). Horak et al. (1988) remarked that the balance test of BOTMP could detect the balance disorders arising due to the peripheral vestibular loss in children with learning disability. Some other scales used by the therapist are: righting and equilibrium reactions (Steindl et al., 2006), Sensory Organization Test (SOT) using posturography (Forssberg & Nashner, 1982) and Pediatric Clinical Test of Sensory Interaction for Balance (Richardson et al., 1992). A laboratory setting on computerized force platform with fixed/moving base or with fixed/moving visual surround, to provide relative movement of body to moving surround is used for posture evaluation. However, the extensive setting and cost limits their use only for research purposes Assessment of Vestibular Dysfunction in Children with Learning Disability Ayres (1972) observed vestibular dysfunctions in some children with learning disability (see section 2.6 of this thesis). Proprioception dysfunctions are usually implicated along with the dysfunction of vestibular system or vice-versa. For all clinical and practical purpose, both these dysfunctions are evaluated and intervened together. The abnormalities of vestibular system are characterized by abnormal nystagmus, muscle hypotonicity and atypical postural responses. Abnormal post-rotatory nystagmus is viewed as most definitive and objective sign of peripheral vestibular dysfunction. However, it s application and interpretation is criticized by Cohen (1989) and Polatjko (1983). The researchers subsequently modified and adapted testing procedures of PRN, but still is not popular tool among the occupational therapists, probably because of strict administrative procedures. Researchers and clinicians recommend standardized tests to infer on status of vestibular functions. However, Bundy, (2002), and other researchers recommended that results of standardized tests be substantiated with clinical methods of motor and postural skills evaluation (Bundy, 2002). Clinical methods form an important part of assessment in daily practice among pediatric occupational therapists, as the standardized assessments are lengthier and some require specialized training for administration and interpretation (e.g. SIPT). Ottenbacher (1978) reported encouraging evidence of clinical based tools to correlate with low PRN scores. However, Short et al. P a g e 32

9 (1983) reported prone extension, standing balance-eyes closed and muscle tone accounted for 37 percent of variance in children with learning disability with low scores on post-rotary nystagmus. Alternatively, therapists often seek behavioral patterns to movements or relation with gravity from interview with parents. Response to swing is also included along with many other situations (such as to vehicle, bouncing in air or to different playground equipment (slide) as part of questionnaire (Dunn, 1994; LaCroix, 1993) exploring vestibular processing deficits. Ayes (1972) observed failure to make adaptive responses to swing as indicative of impairment in the processing of vestibular sensation. In her early research, Ayres (1978) reported that some children with learning-disability were overwhelmed by vestibular stimulation and were unable to make adaptive response. Steinberg and Rendle-Short (1977) observed that children with vestibular dysfunction manifested fear on spinning compared with normal development and those with soft neurological deficits. May-Benson and Koomar (2007) in a pilot study developed an assessment of gravitational insecurity in children on 15 selected tasks such as: jumping, swinging ball, jump off chair, catch the bounced ball. They reported a developmental trend in performance of these tasks in typically developing children, with 9 such tasks able to identify children with gravitational insecurity (and decreased falsepositive identification). However, literature in occupational therapy is scanty about information of adaptive responses on swings in typical children or their difference in atypical children (e.g. with vestibular processing dysfunctions). P a g e 33