Comparative Analysis of Vestibular Asymmetry Parameters in Acute Unilateral Peripheral Vestibulopathy

BACKGROUND AND OBJECTIVES: There are known parameters that indicate vestibular asymmetry, such as directional preponderance (DP) on caloric test, asymmetry on slow harmonic acceleration (SHA) test, asymmetry of time constant (Tc) and slow cumulative eye position (SCEP) on velocity step test. Aim of this study is investigate the sensitivity and predictability of the vestibular asymmetry parameters among them. MATERIALS & METHODS: Twenty six patients who were diagnosed as acute unilateral peripheral vestibulopathy were enrolled in this study. We compared each parameter with site of lesion based on the direction of spontaneous nystagmus and canal paresis (CP) which were totally correlated in this group of patients. RESULTS: Positive predictability of each parameter showed 58% in DP, 62% in SHA asymmetry, 62% in SCEP, 38% in Tc. In the cases that each parameter showed positive result, all of DP and SHA asymmetry indicated site of lesion, and showed high correlation coefficient(r=0.89). But in 27% of SCEP and 23% of Tc did not indicate site of lesion. CONCLUSION: All parameters showed low sensitivity for identifying laterality of lesion even the tests were performed within one week after vertigo attack. DP and VOR asymmetry showed high positive predictability for indicating lesion site.

Analysis of Body Sway and Nystagmus with Galvanic Stimulation in Normal Subjects

BACKGROUND AND OBJECTIVES : The purpose of this study is to evaluate the possibility of clinical application of 'vestibular function test by electrical stimulation' measuring nystagmus and body sway which are generated by electrical stimulation. MATERIALS AND METHODS : Twelve normal subjects for measurement of nystagmus and eight for body sway volunteered to participate as subjects of the experiment. We used continuous direct current from 1mA to 3mA, and its polarity could be switched through the surface electrode on the bilateral mastoid process. Videooculogram was used to measure the nystagmus. Lateral body sway was recorded by using Computerized Dynamic Posturography. RESULTS: When stimulating the positive electrode over the right mastoid, left nystagmus and body sway toward right are observed. When stimulating the negative electrode over the right mastoid, right nystagmus and body sway toward left are observed. The nystagmus occurred 42% at 1mA, 75% at 1.5mA, 92% at 2mA, and 100% at more than 2.5mA. The slow phase velocity of the nystagmus were increased from an average of 1.9 deg/sec at 1mA to an average of 3.6 deg/sec at 3mA. However, they were variable from minimum of 0.1 deg/sec to maximum of 4.8 deg/sec even stimulated with fixed amount of current. Also, the asymmetry of the nystagmus on the each direction was observed over 27% at the stimulation of 2.5mA and 3mA. The body sway was observed on the 7 subjects except one. Among them, body sway occurred on stimulation of 1mA in 5 subjects. CONCLUSIONS : Evaluation of nystagmus with galvanic stimulation revealed high right-left asymmetry in normal subjects and needed more electrical stimulation. Evaluation of body sway with galvanic stimulation is more feasible as a vestibular function test, because it has higher manifestation rate, less asymmetry, and it need less electrical amplitude which cause less discomfort to the subjects.