Unilateral Hypofunction Research Articles

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.

Monothermal differential caloric testing in patients with Meniere's disease

The monothermal differential caloric test allows determination of vestibular recruitment and decruitment, variables which may help discriminate peripheral from central vestibular lesions. Previous reports indicated a strong association between vestibular recruitment and Menière's disease. This study examined patients having unilateral Menière's disease. Nystagmus beat frequency (NBF) and slow-component velocity (SCV) responses were recorded by electronystagmography (ENG). Electronystagmographic findings showing unilateral dysfunction were present in 54% of patients by slow-component velocity and in 31% by nystagmus beat frequency. Unilateral hypofunction was the most frequent lateralizing ENG finding. Absolute vestibular recruitment occurred in less than 10% of patients but relative recruitment was found in nearly 20% of patients. Slow-component velocity had higher sensitivity than nystagmus beat frequency, with excellent clinical concordance. Monothermal caloric testing as described in this study best detects peripheral vestibular disease in Meniere's patients using slow-component velocity to determine unilateral hypofunction and relative vestibular recruitment.

回転眼振検査による一側性前庭補充現象検出の可能性

The possibility of detecting the unilateral recruitment phenomenon in the vestibular system by the rotation test was examined in an analogy model of cochlear recruitment, in which a response from the affected side is characterized by a raised threshold and the intensity of the response above the thresdold asymptotic to that from the normal side.According to the analogy model, the difference of intensity between leftward and rightward rotational nystagmus reaches its maximum at the threshold stimulus intensity of the affected side and keeps that maximum or decreases above the threshold, so that only in patients with mild hypofunction in comparison with the stimulus intensity range can the difference decrease monotonously (“converge”) with the stimulus intensity, as previouly reported. On the other hand, directional preponderence keeps constant below the threshold and decreases above the threshold.Moreover, assuming that the ratio of response to ampullopetal to amullofugal stimulation is 2 : 1, the predicted maximum difference of the nystagmus intensity remains within the normal range of variation when the contribution from spontaneous nystagmus is removed. These results indicate that the unilateral vestibular recruitment phenomenon, when it is similar to cochlear recruitment, is difficult to detect by the rotation test. Directional preponderence usaally comes from unilateral hyperfunction in the acute stage or the compensation process of unilateral hypofunction. These factors are not directly related to vestibular recruitment.

Diagnosis of Unilateral Otolith Hypofunction

Asymmetric vestibular function is the basis of vertigo. Whereas caloric tests can identify unilateral peripheral loss or impairment of horizontal semicircular canal function reasonably accurately, there is as yet no single accepted test of unilateral otolith hypofunction. In some advanced vestibular laboratories around the world, new and perhaps diagnostically useful tests of otolith function are being devised. The physiologic basis and the present clinical applications of these tests are reviewed.

Vestibular asymmetry. Some theoretical and practical considerations.

Pathological vestibular asymmetry can be divided into static and dynamic types. Static asymmetry results from a unilateral change of the resting neural input. Acute, chronic, and recovery stages can be recognized if one interprets the direction and intensity of the resultant spontaneous nystagmus relative to the clinical picture. Static asymmetry is additive with induced asymmetry and manifests itself as directional preponderance or as the direction-fixed or direction-changing feature of positional nystagmus. Dynamic asymmetry refers to abnormal asymmetry induced by normal head movements. For example, with unilateral hypofunction, a greater gain is observed with head movement toward the unaffected side, suggesting nonlinearity as specified by Eswald's second law. Visually induced vestibular asymmetry is a form of dynamic asymmetry generated by convergence of visual-vestibular information, and causing symptoms in certain "motion-active" visual environments.

Normal values in a routine ENG test.

A total of 50 normal subjects were examined by electronystagmography for spontaneous and positional nystagmus. In this way the normal limit of the speed of the slow phase was determined to be 6.5 degrees/sec. By examining 15 of the subjects twice, the normal limit of the mean value of the two results was determined to be 4.5 degrees/sec. Forty-nine of the subjects were calorically tested, using 30 degrees and 44 degrees C stimulation. The results were calculated as indices expressing the degree of unilateral hypofunction and directional preponderance relative to the total caloric excitability. The results were evaluated for the duration of and for the maximum eye speed of the slow phase. The normal limits were determined as the mean value +/- twice the standard deviation. Our results indicate that a left-side hypofunction is a normal phenomenon and that duration and maximum eye speed of the slow phase reflect different aspects of the vestibular function.

Clinical Investigations on Fluctuant Rearing Loss Without Vertigo

1) Ten cases (fourteen ears) with fluctuant hearing loss without vertigo were clinically investigated.2) Hearing loss was seen in low and middle frequencies with positive recruitment. Degree of hearing fluctuation was, in most cases, between 20 and 40dB. Durations between the shift of hearing loss were various in each case, and there was no relation of fluctuating hearing loss to a particular season.3) Four cases of fluctuant hearing loss without vertigo were firstly diagnosed as Meniere's disease.4) Though vertigo was not observed in these cases with fluctuant hearing loss, most cases showed abnormal findings in equilibrium examinations. In caloric test unilateral hypofunction was observed in 60%. While in damped pendular rotationtest, 57% showed abnormal findings suggesting dysfunction or circulatory disturbances in the brainstem.5) Serum lipids, total cholesterol, and glucose torelance test were within normal limits. In two cases abnormal values of serum protein fraction (increase of γ- and α2-globuline) were obtained.It is noteworthy that in these two cases sensorineural hearing losses were improved by administration of steroid (predonine). One of these cases were proved to be aortitis syndrome by aortography.6) Fluctuant hearing loss in these series is a syndrome which include sensori-neural hearingloss due to endolymphatic hydrops (Williams type) or local manifestation of systemic vascular disorders and psychogenic deafness. Therefore, examinations should include not only audiological and vestibular tests but also systemic examinations (BSR, serological tests, endocrine tests, etc.) and studies from psychosomatic standpoint.