Role of posturography in the management of vestibular patients.

Computerized dynamic posturography uses a force platform that can both translate and rotate. When combined with visual stimuli, it can be used to determine the relative importance of the various sensory inputs critical for balance, namely vision, somatosensation, and vestibular sensation. Studies to date have shown several patterns of abnormalities on posturography, the best recognized being the vestibular pattern. Many patients with a high suspicion of having a peripheral vestibular abnormality (based on other information) have such a pattern. Moreover, few normal subjects have such abnormalities. Although computerized dynamic posturography does not help in localizing a lesion or determining its etiology, such testing does provide a functional measure that can be helpful in understanding a patient's ability to properly use vestibular system information. Posturography is helpful in the management of patients with suspected vestibular disorders. In addition to suggesting the presence of a vestibular system abnormality, particularly an uncompensated peripheral vestibular deficit, a bilateral peripheral vestibular deficit, or a central vestibular abnormality, computerized dynamic posturography may help guide the clinician regarding choice of treatment and counseling of patients. Further studies are required to determine the ultimate role of computerized dynamic posturography in the management of patients with vestibular disorders.

Jongkees' formula re-evaluated: order effects in the response to alternate binaural bithermal caloric stimulation using closed-loop irrigation.

Normal limits for the response to caloric irrigation typically are specified as percentage of reduced vestibular response (RVR) and directional preponderance (DP). These measures are calculated using Jongkees' formula without regard to which ear is stimulated first. To assess the influence of the order in which the caloric stimuli are delivered we reviewed the responses to closed loop caloric irrigation of two groups of normal subjects and a group of unselected patients. Results indicated a consistent declining trend in response from the first caloric administration to the last administration in all groups and subgroups except in male patients over 60 years of age. Consequently, a significant bias in RVR was observed. Specifically, with the order of irrigation left cold, right cold, left warm, right warm, the mean percentage RVR for both the patients and control subjects was about a 5% right RVR. The bias resulted in right-sided unilateral hypofunction being diagnosed 2.4 times more often than left-sided hypofunction in patients aged 16-59. Our results differ from the previous literature that describes the effect of order on the response to caloric irrigation; this discrepancy may be related to our use of a closed-loop system for caloric irrigation. We conclude that vestibular laboratories should account for the effect of order in their patients' responses to caloric stimulation. We offer suggestions on how Jongkees' formula can be corrected for the effect of order.

Familial sensorineural hearing loss: a correlative study of audiologic, radiographic, and vestibular findings.

A multidisciplinary approach to the study of a family with autosomal dominant sensorineural hearing loss is presented. The affected family members underwent extensive clinical and laboratory evaluation. They were found to have various degrees of bilateral congenital inner ear anomalies as imaged by computed tomography. The degree of structural abnormalities in the inner ears correlated with the severity of hearing impairment. Vestibular testing revealed nonspecific abnormalities generally correlating with audiologic and radiographic findings. This report presents a unique form of sensorineural hearing loss not previously described and is the first in-depth clinical study of nonsyndromal "Mondini dysplasia" occurring in a family.

Asymmetrical ocular pursuit with posterior fossa tumors.

We report two patients with posterior fossa neoplasms who demonstrated asymmetrically impaired horizontal ocular pursuit documented with electrooculography. One patient had impaired pursuit contralateral to a pontomedullary lesion, whereas the second patient had impaired pursuit ipsilateral to a pontocerebellar lesion. These patients demonstrate that posterior fossa lesions may impair ocular pursuit either contralaterally or ipsilaterally unlike cerebral hemispheric lesions, which impair ocular pursuit ipsilaterally or bilaterally.

Vestibular function in periodic alternating nystagmus.

The vestibulo-ocular reflex of 4 patients with periodic alternating nystagmus (PAN) was studied in detail. Rotational testing was used to investigate the horizontal semicircular canal-ocular reflex, canal-otolith interaction, and the dynamic otolith-ocular reflex. Results indicated abnormal gain and phase of the horizontal semicircular canal-ocular reflex during sinusoidal rotation and a variable rate of decay of postrotatory responses. Each patient had abnormal canal-otolith interaction. An enlarged modulation component of the dynamic otolith-ocular response was observed in each patient. This study supports the idea that PAN is caused by an instability in the velocity storage element, a hypothetical neural circuit that perseverates the eye movement response to both vestibular and optokinetic stimulation. Further, we postulate that PAN may be caused by lesions of the cerebellar uvula and nodulus or their connections with the brainstem vestibular nuclei.

Epileptic nystagmus.

We report a 52-year-old woman with episodes of vertigo accompanied by right beating nystagmus and left posterior temporoparietal sharp waves and spikes on electroencephalogram without change in level of consciousness. Electrooculography demonstrated that the episodes of nystagmus were not preceded by gaze deviation and that nystagmus slow component velocities were linear. This patient's epileptic nystagmus may have been the result of excitation of cerebral ocular pursuit pathways.

Nystagmus responses in a group of normal humans during earth-horizontal axis rotation.

Horizontal eye movement responses to earth-horizontal yaw axis rotation were evaluated in 50 normal human subjects who were uniformly distributed in age (20-69 years) and equally divided by gender for each decade. The subjects were rotated with eyes open in the dark, using clockwise and counterclockwise 60 degree/s velocity trapezoids. The nystagmus slow component velocity (SCV) was analysed using four parameters: Amp, Bias, Mod and Tau. Amp and Tau characterize the canal-ocular reflex to constant velocity steps, while Mod and Bias characterize the "AC" and "DC" components of the otolith-ocular reflex. Results indicated that intersubject variability was larger than that seen in earth-vertical axis data. Tau depended significantly (p less than 0.05) upon subject gender, while Mod increased monotonically with age decade. Linear regression showed a positive correlation between pairs of SCV magnitude parameters (Amp, Bias and Mod), suggesting a common scaling effect. In addition, there was a negative correlation between the value of the decay time constant Tau and each of the three magnitude parameters. Thus, despite large intersubject variability, parameters that describe earth-horizontal yaw axis responses are loosely interrelated and some of them vary significantly with gender and age.

Eighth nerve signs in a case of multiple sclerosis.

We evaluated a 25-year-old woman with multiple sclerosis who presented with the acute onset of a profound unilateral high-frequency, sensorineural hearing loss that resolved clinically within 10 days. Click-elicited brain stem-evoked responses were abnormal at the time of presentation and demonstrated only limited recovery over a follow-up period of 11 months. Magnetic resonance imaging disclosed a lesion in the eighth nerve root-entry zone and the cochlear nucleus. Our findings in this case support the hypothesis of eighth nerve root-entry zone involvement in sudden hearing loss in multiple sclerosis and reinforce the notion that click-elicited brain stem-evoked responses are useful primarily to evaluate the high-frequency regions of the auditory system.

Vestibular responses in Wernicke's encephalopathy.

Two patients with Wernicke's encephalopathy were evaluated with quantitative vestibulo-ocular reflex and ocular motor testing. Vestibulo-ocular reflex testing included caloric irrigation, earth vertical axis rotational sinusoids, and rotational impulses. Both patients demonstrated hypoactive vestibular responses to both caloric and rotational stimuli at the time of presentation. One patient had unbeating nystagmus that diminished with upgaze, downgaze, or convergence. Following treatment with thiamine, both patients' vestibular responses improved but remained abnormal, with a short vestibulo-ocular reflex time constant and increased low-frequency rotational phase lead. Impairment of the velocity storage element attributable to damage to the vestibular nucleus and nucleus prepositus hypoglossi may account for this permanent effect on the vestibulo-ocular reflex.

Central adaptation models of the vestibulo-ocular and optokinetic systems.

A theoretical analysis of two models of the vestibulo-ocular and optokinetic systems was performed. Each model contains a filter element in the vestibular periphery to account for peripheral adaptation, and a filter element in the central vestibulo-optokinetic circuit to account for central adaptation. Both models account for 1 adaptation, i.e. a response decay to a constant angular acceleration input, in both peripheral vestibular afferent and vestibulo-ocular reflex (VOR) responses and 2 the reversal phases of optokinetic after-nystagmus (OKAN) and the VOR and 3 oscillatory behavior such as periodic alternating nystagmus. The two models differ regarding the order of their VOR transfer function. Also, they predict different OKAN patterns following a prolonged optokinetic stimulus. These models have behavioral implications and suggest future experiments.

Long-latency rotational evoked potentials in subjects with and without bilateral vestibular loss.

Human subjects with and without profound bilateral vestibular loss were evaluated using repetitive rotational stimulation about an earth-vertical axis and signal averaging of vertex-recorded potentials. The stimulus events to which averaging was synchronized were acceleration/deceleration pulses produced by abrupt reversals in direction of angular velocity. In control subjects the long-latency rotational evoked potentials elicited via this paradigm were robust and reproducible. The responses of subjects with vestibular loss did not differ remarkably from those of the control subjects. We conclude that the long-latency rotational evoked potential elicited using a conventional rotary chair is not primarily of vestibular origin.

Alternate and simultaneous binaural bithermal caloric testing: a comparison.

This study compares the results from simultaneous binaural bithermal and alternate binaural bithermal caloric testing of 652 patients with dizziness. Also compared are the abilities of these tests to distinguish between a population of healthy asymptomatic subjects and our patient population. Caloric testing used a closed-loop irrigation system. Eye movements were monitored with electro-oculography. The agreement between the results from the two tests was low. Also, while the simultaneous test was more sensitive, the alternate test was more specific. Using receiver-operator characteristic methodology, it was found that the ability of the alternate test to distinguish between a healthy population and a patient population was superior to that of the simultaneous test. There was no improvement in the ability to distinguish between a healthy population and a patient population when the results from the two tests were combined as compared to using the alternate caloric test alone.

Spontaneous remission of paraneoplastic ocular flutter and saccadic intrusions.

We report two women with ocular flutter and saccadic intrusions, documented by electro-oculography, who had complete spontaneous remission of their ocular motor findings prior to the appearance of a primary neoplastic process remote from the nervous system. Transient elevation of blood HVA and VMA levels was detected in one patient who subsequently had breast cancer. These cases indicate that spontaneous remission of saccadic oscillations does not necessarily imply a benign outcome. Patients with this ocular motor abnormality should be followed closely for signs of a remote neoplasm even if initial investigation is negative.