Significance of Correcting the Spontaneous Nystagmus in Siusoidal Harmonic Acceleration Test / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: Spontaneous nystagmus may have an influence on the results of sinusoidal harmonic acceleration (SHA) test, although it has not been ascertained through sufficient studies. This study evaluated the effect of spontaneous nystagmus on the gain, asymmetry and phase values of the SHA test. SUBJECTS AND METHOD: We retrospectively analyzed 19 patients with acute unilateral vestibular weakness and spontaneous nystagmus (sn). All patients underwent a battery of vestibular testing including videonystagmography, bithermal caloric test, and SHA test. Gain, asymmetry, and phase were calculated with the conventional method without correcting for sn, thus the non-corrected SHA (nSHA). Then the same three parameters were calculated again after manually correcting for spontaneous nystagmus, thus the corrected SHA (cSHA). The two methods were compared with respect to gain, asymmetry and phase values. Correlation between the SHA test and caloric test was also analyzed. RESULTS: The gain of nSHA was significantly larger than that of cSHA in all frequencies. There was no difference in the phase values between the two analysis methods. The asymmetry of nSHA was 2.8 times larger than that of cSHA. The asymmetry values of both nSHA and cSHA showed a significant correlation between the caloric test and degree of spontaneous nystagmus. CONCLUSION: It seems that the SHA test is significantly influenced by spontaneous nystagmus. Although correcting for spontaneous nystagmus may not always be necessary, we should consider the effect of spontaneous nystagmus when interpreting the SHA test results of a patient who has spontaneous nystagmus.

New Proposal of Functional Status of Vestibular System Based on Vestibular Function Tests Findings in Dizzy Patients with Normal Caloric Response / 대한평형의학회지

BACKGROUND AND OBJECTIVES: Vestibular function tests are very useful in diagnosing dizzy patients. Among them, bithermal caloric test is most commonly used test for localizing their permanent vestibular loss. However, it causes much discomfort to the patients with non-physiologic stimuli. In addition, it doesn't represent the present functional status of vestibular system. Therefore, normal caloric result does not accurately correspond to normal vestibular function in dizzy patients. Currently, rotation chair test and dynamic posturography have been introduced adjunctly to assess vestibular function accompanied by bithermal caloric test. It has not been elucidated for their specific role in diverse settings of vestibular disorders. So we planned this study to evaluate clinical usefulness of rotation chair test, videonystagmography and computerized dynamic posturogr-phy in dizzy patients with normal caloric response. MATERIALS AND METHODS: We reviewed clinical records of 46 patients who met their inclusion criteria. They were categorized into five subgroups according to abnormal vestibular function test findings. RESULTS: In each subgroup, we hypothesized its clinical relevance, possible mechanism of dizz-iness and presumed diagnosis. Five categories are as below; visual dependency, imbalance of vestibular tones, chronic peripheral vestibulopathy, abnormality in the vestibulospinal tract and abnormality of oculomotor system. CONCLUSION: We suggest new classification of abnormal vestibular functional status in dizzy patients with normal caloric results. These are comparable according their clinical features and thought to be helpful in managing and counseling each patient.

Clinical Implication of High VOR Gain in Slow Harmonic Acceleration / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: The purpose of this study was to verify if high vestibulo-ocular reflex (VOR) gain in slow harmonic acceleration (SHA) test can be considered as a hallmark of a distinct disease entity. We hypothesized that patients with high VOR gain in the SHA test can be classified as a distinct disease group and looked for evidence that can support this hypothesis. SUBJECTS AND METHOD: For this study, 306 patients who had undergone a rotation chair test were enrolled. We checked other VOR measurements (caloric test and step velocity) and clinical manifestation of the patients with high gain in SHA (HG group). The data were compared to those of the migraine associated vertigo (MAV), benign recurrent vertigo (BRV) and psychogenic dizziness (PsyD). RESULTS: An abnormally long time constant and a large response to the caloric test were found more frequently in the patient group with high gain in SHA. The incidence of high gain in SHA was significantly higher in MAV, BRV and PsyD. The clinical manifestation of HG group was not distinguishable from the effects of BRV and PsyD. But MAV was different from HG group. CONCLUSION: We failed to find any evidence that the patients with high gain in the SHA could be classified as a distinct disease group. It seems that high gain is not merely a non-specific or incidental finding but a reproducible finding that reflects an aspect of the subject's vestibular function. Also, the high gain in SHA is more suggestive of BRV or PsyD than MAV.

Evaluation of Compensation in Peripheral Vestibulopathy / 대한이비인후과학회지

The initial severe and disabling symptoms of vestibular dysfunction diminish gradually by a process of compensation. Although the process is complex and not fully understood, knowledge of the extent of compensation makes physicians to identify the causes and to determine treatment choices of the dysfunction. In this report we present 2 common cases of peripheral vestibulopathy that result from different disease processes, and review the physiologic and functional changes as the compensation proceeds that can be evaluated by vestibular function tests including electronystagmography(ENG), rotation chair, and dynamic posturography. These tests are valuable tools in the assessment of the degree of compensation as well as the side and site of lesions in vestibulopathy.