Measures of activity restriction The DHI, VADL, and ABC are all measures that focus on determining the level of limitation of activity in daily life in patients with vestibular dysfunction. The DHI is the most widely used self-assessment tool in patients with vestibular disorders. It assesses the emotional, functional, and physical impact of vestibular disease over 25 items using a 3-point scale. The total score is obtained by summing the subscale scores, to a maximum score of 100 points, with higher scores indicating more severe disability (Jacobson & Newman, 1990). Although the DHI cannot guide treatment because it does not indicate specific tasks or activities that cause the patient’s symptoms, it has been shown to be well correlated with level of functional impairment as measured by the Five Times Sit-to-Stand test, ABC, and incidence of falling (Whitney, Wrisley, et al., 2004). The VADL assesses the impact of vestibular dysfunction on activities of daily life. It uses 28 items to measure level of disability in the domains of basic self-care, mobility, and instrumental activities of daily living (Cohen & Kimball, 2000). The items on the VADL do not address the symptoms or emotional component of vestibular dysfunction, but rather focus on domains of function. The VADL has been shown to be moderately correlated with the DHI and is able to detect changes in function after vestibular rehabilitation (Cohen & Kimball, 2003), although the Minimally Clinically Important Difference (MCID) psychometrics have not been established. The FES assesses fear of falling during activities of daily living in the older adult population. The 10-item scale asks patients to rate their confidence in being able to perform activities without falling. Activities rated include getting out of bed, reaching into cabinets, and getting dressed (Tinetti et al., 1990). The FES is an appropriate tool to use for the frail older adult, but scores have been shown to skew toward 100% confidence in the community- dwelling older adult due to the low physical demand of the items scored (Maki et al., 1991).
The ABC was established to assess self-perceived balance confidence in performing 16 common daily activities in the community-dwelling older adult population (Powell & Myers, 1995). The stem question asks patients to rate their level of confidence (“How confident are you that you will not lose your balance or become unsteady…”) in performing activities such as walking up and down the stairs, getting on and off an escalator, and walking in a crowded mall. The average of all scores is calculated, with higher percentages indicating greater confidence in balance. The ABC has been extensively studied and has been found to have good correlation with the FGA (Wrisley & Kumar, 2010), and is strongly correlated with the BBS and TUG in the community-dwelling older adult population (Hatch et al., 2003). In patients with vestibular dysfunction, the ABC has also been shown to have excellent correlation with the DHI (Whitney, Hudak, et al., 1999) and good correlation with the DGI (Marchetti et al., 2011). A cutoff score of 67% (and below) has been established to predict fall risk in the community-dwelling older adult population with 84.4% sensitivity and 87.5% specificity (Lajoie & Gallagher, 2004). An important note to clinicians is the finding that although the ABC is intended to be administered as a self-report measure, it has been determined that patients find the stem questions difficult to interpret, responding in terms of whether they perform the activity, rather than their level of confidence should they encounter the activity. Thus, studies have determined that this tool would be best administered by interview (Hatch et al., 2003; Powell & Myers, 1995). The Life Space Assessment (LSA) is a self-report clinical assessment of the achieved “life space” over the previous month, ranging from movement in the home, to in the neighborhood, to out of the town. It also asks about the amount of movement, the need for assistance, and the use of an assistive device. The LSA has been found to have concurrent validity with the DHI and good test-retest reliability (Alshebber et al., 2020).
MEDICAL EXAMINATION OF VESTIBULAR DYSFUNCTION
In addition to the “bedside” clinical examination of vestibular function, there are a number of vestibular function tests that are performed in a laboratory setting. These are caloric tests, rotational chair testing, and vestibular evoked myogenic potentials. The caloric exam is considered part of the “gold standard” for identifying unilateral peripheral vestibular hypofunction. While clinical tests for peripheral vestibular hypofunction involve head movements, which essentially assess both sides simultaneously, caloric tests can determine the side of the deficit because each side is tested separately. These tests systematically introduce warm and cold air or water into the external auditory canals, creating a temperature gradient across the horizontal canal and subsequent endolymph flow. Warm temperatures cause an excitation response, generating lateral nystagmus with the fast phase beating toward the test ear. Conversely, cool temperatures create an inhibitory response, generating a lateral nystagmus away from the test side. A reduced or absent response (no nystagmus) is indicative of vestibular hypofunction or loss. The caloric test has inherent limitations. The first is that it stimulates only horizontal canal function, and thus assesses afferent activity only from the superior vestibular nerve. It also generates a low frequency of stimulation; thus, it may not accurately measure vestibular function. Finally, it is not well tolerated by many patients (Jacobson & Shepard, 2008). Rotational chair testing is another “gold standard” test to identify bilateral vestibular hypofunction. This is a sophisticated test to measure VOR gain (ratio of head-eye movement), VOR symmetry (right and left rotations), and VOR phase (relationship of head and eye position). In this test, the patient
is securely seated in a mechanical chair that will rotate at a variety of velocities, typically 60°/second and 240°/second. Electromyogram (EMG) recordings track eye movement both during rotation and upon stopping to measure VOR metrics, which identifies presence and degree of vestibular hypofunction on each side. As with caloric testing, the rotational chair test only measures components of horizontal canal function. Vestibular evoked myogenic potentials (VEMP) measure otolith function. The neurophysiological basis for VEMP testing starts with the knowledge that otoliths can be stimulated by vibration and high-level acoustical inputs. The cervical vestibular evoked myogenic potential (cVEMP) test uses loud clicks to evoke stimulation of the sacculus and inferior vestibular nerve. Thus, sound-evoked otolith activity will elicit postural responses through the VSR pathway. The EMG activity of the sternocleidomastoid muscles are used as a measure of otolith function. In the ocular VEMP (oVEMP), vibration over the center of the forehead is used to stimulate utricle activity, resulting in an excitatory response of the inferior oblique muscles (Jacobson & Shepard, 2008). Although these tests provide more sophisticated and diagnostic information regarding vestibular function, they are not performed routinely given the need for highly specialized equipment and highly trained staff, and the time-consuming nature of the tests. However, the clinician working with patients with vestibular disease must be able to appreciate the diagnostic value of these test results that may be part of the patient’s initial work-up.
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