The effect of hearing loss on ABR interpretation: use of a correction factor.

Patients suspected of retrocochlear disorders often have abnormal ABRs in the presence of high-frequency hearing loss, making clinical decisions difficult. In a retrospective study of the ABR test results of 1539 patients, the false-positive and false-negative rates for ABR are presented as a function of hearing loss at 4000 Hz, both before and after using Selters and Brackmann's correction factor for hearing loss. For patients with more than 50 db HL at 4000 Hz the false-positive and false-negative rates, uncorrected for hearing loss, were 25.0% and 2.9% respectively, and when the correction factor was used were 12.5% and 5.8%. When hearing loss at 4000 Hz was over 90 dB the ABR was abnormal in 75% of nontumor patients. Conclusions are that a correction factor for hearing loss is helpful with reservations, and that ABR is not a useful test when 4000 Hz hearing loss is greater than 90 dB HL and 2000 Hz is greater than 75 dB HL.

On the search for markers of poor vestibular compensation.

The effectiveness of pursuit gain, cancellation of the vestibulo-ocular reflex, and a clinical oscillopsia test were assessed as vestibular function tests and tests that may allow prediction of which patients would compensate poorly after vestibular surgery. Cancellation of the vestibulo-ocular reflex in 17 patients and 17 control subjects was compared. Pursuit gain for 17 patients was determined for three frequencies at peak velocities of 25 and 50 degrees/sec. The oscillopsia test was administered to seven patients during at least the first 6 postoperative months. We are unable to state that any of these parameters were effective "markers" of impaired compensation, but the oscillopsia test appears to be a useful clinical tool for vestibular examination.

Changes in the time constants of the vestibulo-ocular reflex and optokinetic afternystagmus following unilateral ablative vestibular surgery.

Changes in the time constants and gains of the vestibulo-ocular and optokinetic systems were studied in seven patients. Angular acceleration pulse and optokinetic stimuli were administered to three normal subjects and also to seven patients at specific intervals after unilateral ablative vestibular surgery. The gains and the time constants of the two systems were compared. Regression analysis showed that the vestibulo-ocular and optokinetic time constants for slow phase eye movements away from the ablated ear declined significantly after surgery in the patient group, but that the gains did not. A theory based upon variability of system parameters by the CNS is outlined to explain the changes in the dynamics of the two systems after surgery. The data from this study suggest that the time constant may be a useful parameter in clinical vestibular testing.

Bilateral vestibular loss and oscillopsia.

The electronystagmographic (ENG) records of 5,499 patients were reviewed so as to note the level of caloric activity. Bilateral caloric reduction or loss was found in only 1.6%. Although no diagnosis could be made with a high degree of confidence in the majority of patients, bilateral Ménière's disease and exposure to ototoxic drugs were identified most frequently. The degree of caloric reduction or loss did not correlate with the subjective symptom of oscillopsia, oscillopsia test findings or results of low frequency harmonic sinusoidal rotation tests. In a few patients with bilateral caloric loss, no oscillopsia was demonstrated. Many mechanisms other than the vestibulo-ocular reflex exist to provide visual stability, and we assume these become effective in some patients with bilateral caloric reduction or loss.

Psychiatric diagnoses in patients with psychogenic dizziness or severe tinnitus.

Psychiatric assessments were made of patients with psychogenic dizziness (N = 17) and severe tinnitus (N = 24) using the Structured Clinical Interview for DSM-III-R (SCID). The psychogenic dizziness group had a high prevalence of psychiatric disorders (100%), the majority being anxiety disorders (94%), particularly diagnoses in the panic-agoraphobic cluster (76%). The severe tinnitus group had a lower prevalence of psychiatric disorders (63%) with a predominance of mood disorders (46%). Those tinnitus patients with no hearing loss tended to have more diagnoses per patient and more anxiety disorders than those with hearing loss. Although this was not a random sampling of these patients populations, the results are of sufficient magnitude to warrant further studies. The implications of the results are discussed in terms of treatment and future research.

The reproducibility of caloric tests of vestibular function in young and old subjects.

The test-retest repeatability of the hot caloric response alone and of the hot and cold caloric responses combined, was evaluated in 29 subjects, over a 6-month period. The subjects were from two different age groups, 20-30 years (15 subjects) and 65-75 years (14 subjects). Intersubject variability was statistically significant in both age groups, though of greater magnitude in the older subjects. Once a vestibular caloric response baseline was established, for any given subject, there was reasonably reliable test-retest repeatability over time, in both age groups, with coefficients of reliability greater than 0.90.

Vertical nystagmus in routine caloric testing.

Vertical nystagmus may occur in caloric testing when only horizontal is expected. We examined this occurrence in 112 normal subjects and in 339 patients with dizziness. Vertical nystagmus was found in 29 percent of normals and in 12 percent of patients with dizziness, more often with hot than cool caloric stimuli and it is always accompanied by horizontal nystagmus. The finding occurred with peripheral and central nervous system diagnoses as well as with patients whose dizziness was considered psychogenic or was undiagnosed. Maximum slow component velocity (SCV) of vertical nystagmus was usually half or less than that of the nystagmus in the horizontal lead. The SCV time profiles of the nystagmus in horizontal and vertical leads differed considerably. Possible origins of vertical nystagmus are discussed. Whatever the origin, it is clear that the finding of vertical nystagmus in routine caloric testing does not automatically denote disease of the central nervous system.

Diagnoses in a dizziness unit.

Data are given on 2,515 patients who attended the Dizziness Unit on 3,113 visits. The sex incidence was 58% female, 42% male, and the sex preference most marked in the psychogenic group from ages 20 to 50. Dizziness is mainly a condition of middle-age; with a steadily aging population we can expect a disproportionate increase in patients with dizziness. Psychogenic dizziness was the commonest of all diagnoses (21.1%), followed closely by "undiagnosed"; together, these two comprised 40% of all diagnoses. Obviously, they deserve more clinical attention than such relatively rare conditions as delayed endolymphatic hydrops (0.5%) or inner ear fistula (0.4%). For all diagnostic categories, on repeated visits the original diagnosis was changed in about one-third of cases. Diagnostic conversion was most frequent in "undiagnosed", at a level of 58%.

Recurrent vestibulopathy: third review.

The term "recurrent vestibulopathy" is used to distinguish patients with multiple episodes of vertigo of duration varying from about 5 minutes to 24 hours, without auditory or neurological symptoms or signs. About 70% retain the original diagnosis on mean follow-up of both 5.5 and 8.5 years, while the balance (at both intervals) convert either to Meniere's Disease or benign postural vertigo. We think that periodic reduction of afferent discharge activity in one vestibular nerve is the mechanism of the episodes, and virus the probable cause.

Bilateral vestibular loss, oscillopsia, and the cervico-ocular reflex.

Oscillopsia during head movement occurs in patients with bilateral vestibular loss and may be transient or persistent. To investigate mechanisms underlying recovery we tested the vestibulo-ocular reflex (VOR), visual-vestibular interaction, and the cervico-ocular reflex (COR); we used a pseudorandom oscillatory stimulus with a frequency band width of 0 to 5 Hz in six patients with bilaterally absent caloric responses and in 10 normal controls. Seven control subjects had low-gain COR responses, but these were anticompensatory with respect to the VOR. Three asymptomatic patients with an absent or grossly deficient VOR had increased oculomotor responses at all frequencies when oscillated in light. Compensatory COR responses were detected in these patients but not in patients with persisting oscillopsia. In some patients with bilateral vestibular loss, augmented cervico-ocular and visual reflexes may compensate, at least partially, for an absent VOR.

Positional nystagmus.

Positional nystagmus may be persistent or transitory. Of the persistent forms, type I refers to nystagmus changing direction in different head positions and type II to nystagmus beating in a single direction. Both types may denote either peripheral or central abnormality. Transitory, or paroxysmal, positional nystagmus is classified as type III, and the history and physical and electronystagmographic features of its accompanying vertigo and nystagmus permit subdivision into typical and atypical forms. Guidelines are given for the differentiation of typical and atypical forms. In the great majority of cases type III positional nystagmus denotes a harmless inner ear disturbance, but the occasional serious intracranial lesion is also causative. Most instances of the latter, but not all, will fit in the atypical group. A case is reported of vermis metastasis with presenting features of postural vertigo and paroxysmal downbeat positional nystagmus.

Head and eye movements in congenital nystagmus.

Patients with congenital nystagmus exhibit a wide range of unusual nystagmus waveforms and strategies to obtain maximum visual acuity. We investigated target acquisition strategies, head-eye coordination, and the effects of alteration of head position relative to gravity on congenital nystagmus waveforms in five patients. No changes in the nystagmus were found when patients' heads were placed in different positions relative to gravity. Two patients had distinctive abnormalities of head-eye coordination characterized both by failure of eye movement to precede head movement and by position of the eye in the orbit, after target acquisition, being in a direction opposite that of the head movement. We conclude that static changes in head position relative to gravity probably do not influence congenital nystagmus waveforms. In addition, some patients with congenital nystagmus may have abnormal head-eye coordination.

Optokinetic afternystagmus and post rotatory nystagmus in patients with unilateral labyrinthine lesions.

The decay times of optokinetic afternystagmus (OKAN) and the vestibuloocular reflex (VOR) were measured in six subjects with chronic unilateral labyrinthectomy and in six age-matched controls. Both OKAN and VOR decay times showed parallel reduction following unilateral labyrinthectomy when the induced nystagmus beat toward the side of the lesion. The VOR decay time for nystagmus beating toward the contralateral side was also significantly reduced. Our findings support the view that the optokinetic system increases the vestibular decay time, that separate left and right velocity storage mechanisms do exist, but that the decoupling between the two sides is far from perfect.

Results of endolymphatic sac surgery for Ménière's disease.

From 1976 to 1982, 72 patients with Ménière's disease had endolymphatic sac surgery. Sixty of the 72 were reviewed after a mean period of 33 months from operation; in these, sac surgery (regardless of type) provided abolition or improvement of vertigo in 75%, and 70% of these had hearing improvement or stabilization. Twelve had failure of vertigo control and required either labyrinthectomy or vestibular neurectomy, usually within one year of the first operation. In a smaller subgroup followed for a mean period of 51 months, vertigo control was achieved in 60% and hearing maintenance in 40%. Our data indicate that sac surgery provides good control of vertigo and maintenance of hearing for a period up to about three years, with a significant decline in benefit at about four or five years after operation.

Histopathological findings in clinical gentamicin ototoxicity.

The temporal bone histopathological findings in a case of gentamicin sulfate-induced hearing loss and vertigo in an anephric patient undergoing hemodialysis are presented. A study of the sensory neuroepithelium of the cristae and maculae disclosed the presence of vacuoles with clubbing of the sensory cells. In the cochlea, loss of the innermost row of outer hair cells in the basal turn was the most prominent feature. These findings are discussed in light of reports of similar morphological changes in laboratory studies of gentamicin ototoxicity.

Positional vertigo and nystagmus of central origin.

Four cases are described illustrating the clinical features of positional vertigo and nystagmus due to posterior fossa tumors and a case of obstructive hydrocephalus. In these cases positional vertigo was the first and only presenting symptom of central nervous system disease. One case of subependymoma of the fourth ventricle and one with hydrocephalus had characteristic symptoms of benign positional vertigo; each showed positional nystagmus of the benign paroxysmal type.

Measurement of optokinetic nystagmus for otoneurological diagnosis.

Optokinetic nystagmus was recorded and measured in 101 subjects comprising six diagnostic categories: 1) normal, screened for otologic disease, 2) chronic unilateral labyrinthectomy, 3) unilateral Menière's disease, 4) neurologically confirmed focal brainstem lesion, 5) brainstem-cerebellar syndrome, and 6) focal unilateral supratentorial lesion. For the OKN test, each subject looked at a translucent screen onto which a field of parallel black and white bars was back-projected. The array of bars could be projected vertically or horizontally to allow for study of nystagmus beating right and left or up and down. The speed of movement of the bars varied over a range from 20 to 140 degrees/sec of visual angle, in each axis for both directions. An analysis of the slow phase velocity of OKN indicated that patients with brainstem disease produced significantly lower eye speeds than did normal subjects or patients with chronic peripheral vestibular disease. The latter groups could not be distinguished. The responses of patients with cortical lesions fell midway between these two extremes and were significantly different from those of the brainstem group. Directional preponderance of nystagmus proved to be significantly related to the side of lesion for both the labyrinthine and cortical groups. However, the absolute value of the difference in slow phase velocity for nystagmus beating toward or away from the side of lesion was no greater than the difference between right and left-beating nystagmus in normal subjects. While the results provide statistical confirmation for the findings of earlier investigations, it is noted that for purposes of clinical diagnosis, the test is of value only in the context of the otoneurological test battery. Distribution of results for individuals in the various groups overlap considerably. The designation of a numerical cutoff for differential diagnosis leads to error rates far in excess of what may be confidently attributed to chance.