Phillip D. Cremer

Dehiscence of bone overlying the superior canal as a cause of apparent conductive hearing loss.

Objective To identify patients with superior semicircular canal dehiscence and apparent conductive hearing loss and to define the cause of the air-bone gap. Study Design Prospective study of patients with superior canal dehiscence. Setting Tertiary referral center. Patients Vestibular and/or auditory findings indicative of canal dehiscence and demonstration of superior canal dehiscence on computed tomography of the temporal bone. Intervention Vestibular-evoked myogenic potentials, three-dimensional eye movement recordings, and surgical resurfacing of the superior canal. Outcome Measure Association of superior canal dehiscence with an air-bone gap on audiometry. Results Four patients with dehiscence of bone overlying the superior canal were found to have air-bone gaps in the affected ears that were greatest at lower frequencies and averaged 24 ± 7 dB over the frequency range of 250 to 4,000 Hz. Three of these patients had undergone stapedectomy before the identification of superior canal dehiscence. The air-bone gap was unchanged postoperatively. Each patient had an intact vestibular-evoked myogenic potential (VEMP) response from the affected ear, a finding that would not have been expected based on a middle ear cause of conductive hearing loss. One patient underwent resurfacing of the superior canal through a middle fossa approach. Postoperatively, his vestibular symptoms were relieved, and his air conduction thresholds were improved by 20 dB. Conclusions Superior canal dehiscence can result in apparent conductive hearing loss. The third mobile window created by the dehiscent superior canal results in dissipation of acoustic energy and is a cause of inner ear conductive hearing loss.

Symptoms and signs in superior canal dehiscence syndrome.

Abstract: Patients with superior canal dehiscence (SCD) syndrome experience vertigo and oscillopsia in response to loud sounds and to stimuli that result in changes in middle ear or intracranial pressure. They may also experience hyperacusis to bone‐conducted sounds. The evoked eye movements in this syndrome align with the plane of the dehiscent superior canal. The symptoms and signs can be understood in terms of the effect of the dehiscence in creation of a third mobile window into the inner ear. The SCD syndrome has been diagnosed in 28 patients who were examined in the neuro‐otology clinics at the Johns Hopkins Medical Institutions from May 1995 through January 2001. The diagnosis is best established based upon the symptoms that are characteristic for the syndrome, the vertical‐torsional eye movements evoked by sound or pressure stimuli noted on examination performed with Frenzel goggles, the lowered thresholds for responses to vestibular‐evoked myogenic potentials, and CT imaging of the temporal bones.

Vestibular, saccadic and fixation abnormalities in genetically confirmed Friedreich ataxia

Friedreich ataxia (FRDA), the commonest of the inherited ataxias, is a multisystem neurodegenerative condition that affects ocular motor function. We assessed eye movement abnormalities in 20 individuals with genetically confirmed FRDA and compared these results to clinical measures. All subjects were assessed with infrared oculography. Fifteen individuals underwent a full protocol of eye movement recordings. Ten subjects were analysed using two-dimensional scleral coil equipment and five using three-dimensional scleral coil recording equipment. We also recorded visual quality of life, Sloan low contrast letter acuity and Friedreich Ataxia Rating Scale scores to compare to the visual measures. Whilst saccadic velocity was essentially normal, saccadic latency was prolonged. The latency correlated with clinical measures of disease severity, including the scores for the Friedreich Ataxia Rating Scale and the Sloan low contrast letter acuity tests. Fixation abnormalities consisting of square wave jerks and ocular flutter were common, and included rare examples of vertical square wave jerks. Vestibular abnormalities were also evident in the group, with markedly reduced vestibulo-ocular reflex gain and prolonged latency. The range of eye movement abnormalities suggest that neurological dysfunction in FRDA includes brainstem, cortical and vestibular pathways. Severe vestibulopathy with essentially normal saccadic velocity are hallmarks of FRDA and differentiate it from a number of the dominant spinocerebellar ataxias. The correlation of saccadic latency with FARS score raises the possibility of its use as a biomarker for FRDA clinical trials.

Changes in the three-dimensional angular vestibulo-ocular reflex following intratympanic gentamicin for Ménière's disease

The 3-dimensional angular vestibulo-ocular reflexes (AVOR) elicited by rapid rotary head thrusts were studied in 17 subjects with unilateral Ménières disease before and 2–10 weeks after treatment with intratympanic gentamicin and in 13 subjects after surgical unilateral vestibular destruction (SUVD). Each head thrust was in the horizontal plane or in either diagonal plane of the vertical semicircular canals, so that each head thrust effectively stimulated only one pair of canals. The AVOR gains (eye velocity/head velocity during the 30 ms before peak head velocity) for the head thrusts exciting each individual canal were averaged and taken as a measure of the function of that canal. Prior to intratympanic gentamicin, gains for head thrusts that excited canals on the affected side were 0.91 ± 0.20 (horizontal canal, HC), 0.78 ± 0.20 (anterior canal, AC), and 0.83 ± 0.10 (posterior canal, PC). The asymmetries between these gain values and those for head thrusts that excited the contralateral canals were <2%. In contrast, caloric asymmetries averaged 40% ± 32%. Intratympanic gentamicin resulted in decreased gains attributable to each canal on the treated side: 0.40 ± 0.12 (HC), 0.35 ± 0.14 (AC), 0.31 ± 0.14 (PC) (p <0.01). However, the gains attributable to contralateral canals dropped only slightly, resulting in marked asymmetries between gains for excitation of ipsilateral canals versus their contralateral mates: HC: 34% ± 12%, AC: 24% ± 25%, and PC: 42% ± 13%. There was no difference in the AVOR gain for excitation of the ipsilateral HC after gentamicin in patients who received a single intratympanic injection (0.39 ± 0.11, n = 12) in comparison to those who received 2–3 injections (0.42 ± 0.15, n = 5, p = 0.7). Gain decreases attributed to the gentamicin-treated HC and AC were not as severe as those observed after SUVD. This finding suggests that intratympanic gentamicin causes a partial vestibular lesion that may involve preservation of spontaneous discharge and/or rotational sensitivity of afferents.

Impulsive Testing of Individual Semicircular Canal Function

Abstract: In order to test the human angular vestibulo‐ocular reflex in the dynamic range of normal head movements, we measured 3‐dimensional compensatory eye‐movement responses to low‐amplitude (10–12°), high‐acceleration (3000–4000°/s/s), passive, manually delivered head rotations (head “impulses”) in the three planes of the semicircular canals in normal subjects, in subjects who had recovered from surgical unilateral vestibular deafferentation, and in patients after acute unilateral peripheral vestibulopathy, that is, from vestibular “neuritis.” We found that canal‐plane head impulses away from an intact semicircular canal, that is, toward a lesioned semicircular canal, invariably produce a vestibulo‐ocular reflex with permanently low gain, typically less that 0.4 if the lesion is complete. These results are a necessary consequence of primary semicircular canal afferents being driven into inhibitory saturation by rapid angular accelerations. With practice, clinicians can learn to recognize the telltale compensatory saccades that patients with unilateral loss of semicircular canal function will make if asked to look at an earth‐fixed target during head impulses in any one of the three semicircular canal planes.

Vestibulo-ocular reflex pathways in internuclear ophthalmoplegia

We measured the vestibulo‐ocular reflex (VOR) during head impulses in a patient with right‐sided internuclear ophthalmoplegia. Head impulses are rapid, passive, high‐acceleration, low‐amplitude head rotations in the direction of a particular semicircular canal (SCC). Adduction of the right eye was abnormally slow during right lateral SCC head impulses. The VOR during left posterior SCC impulses was severely deficient in both eyes, but the VOR during left anterior SCC impulses was only slightly deficient. We suggest that the vertical vestibulo‐ocular pathways in humans are connected in SCC‐plane coordinates, not the traditional roll and pitch coordinates, and that anterior SCC signals do not travel exclusively in the medial longitudinal fasciculus. Ann Neurol 1999;45:529–533

Cognitive behavior therapy for chronic subjective dizziness: a randomized, controlled trial☆

PURPOSE The aim of this study was to evaluate the effects of a brief cognitive behavior therapy (CBT) intervention on the physical symptoms, illness-related disability, and psychologic distress of patients with chronic subjective dizziness. MATERIALS AND METHODS Forty-one patients with chronic subjective dizziness referred by a neurootologic clinic were randomly assigned to immediate treatment or a wait-list control. Three weekly treatment sessions based on the CBT model of panic disorder, adapted for patients with dizziness, were administered by a clinical psychologist. Treatment included psychoeducation, behavioral experiments, exposure to feared stimuli, and attentional refocusing. Outcomes were measured on the Dizziness Handicap Inventory and the Depression, Anxiety and Stress Scales. Two further measures developed for this study; the Dizziness Symptoms Inventory and the Safety Behaviours Inventory were used to measure physical symptoms and safety behaviors. RESULTS The intervention was associated with significant reductions in disability on the Dizziness Handicap Inventory, reduced dizziness and related physical symptoms on the Dizziness Symptoms Inventory, and reduced avoidance and safety behaviors as measured by the Safety Behaviours Inventory. Pre- to posteffect sizes ranged from 0.98 to 1.15. There was no change in psychologic outcomes measured on the Depression, Anxiety and Stress Scales. CONCLUSIONS A 3-session psychologic intervention based on the CBT model can produce significant improvements in dizziness-related symptoms, disability, and functional impairment among patients with chronic subjective dizziness. This suggests that treatment of this condition may be reasonably simple and cost-effective for most of the patients.

Disruption to higher order processes in Friedreich ataxia.

Friedreich ataxia (FRDA), the most common of the genetically inherited ataxias, is characterised by ocular motor deficits largely reflecting disruption to brainstem-cerebellar circuitry. These deficits include fixation instability, saccadic dysmetria, disrupted pursuit, and vestibular abnormalities. Whether higher order or cognitive control processes involved the generation of more volitional eye movements are similarly impaired, has not been explored previously. This research examined antisaccade and memory-guided saccade characteristics in 13 individuals with genetically confirmed FRDA, and contrasted performance with neurologically healthy individuals. We demonstrate, for the first time, a broad range of deficits in FDRA consistent with disruption to higher order processes involved in the control of saccadic eye movement. Significant differences between FDRA and control participants were revealed across all movement parameters (latency, gain, velocity, position error), and across all saccade types, including alterations to velocity profiles. FDRA participants also generated significantly more erroneous responses to non-target stimuli in both saccade paradigms. Finally, a number of correlations between ocular motor and clinical measures were revealed including those between contrast acuity and saccadic latency (all saccade types), disease duration and measures of response inhibition (errors and relative latencies for antisaccades), and neurological scores and error latencies, arguably a reflection of difficulty resolving response conflict. These results suggest a role for the cerebellum in higher order cognitive control processes, and further support the proposal that eye movement markers, which can be measured with accuracy and reliability, may be a useful biomarker in FDRA.

Posterior semicircular canal nystagmus is conjugate and its axis is parallel to that of the canal

Article abstract A patient with a postoperative fistula of the left posterior semicircular canal is presented. Negative pressure in the external ear canal produced upbeat-torsional nystagmus, which was recorded in three dimensions using binocular scleral search coils. The nystagmus was conjugate, without skew deviation, and its trajectory corresponded to the anatomic axis of the left posterior canal. The current study helps validate Ewald’s first law in humans: the axis of nystagmus should match the anatomic axis of the semicircular canal that generated it. This law is clinically useful in diagnosing pathology of the vestibular end-organ, such as benign paroxysmal positional vertigo or the superior semicircular canal dehiscence syndrome.

Changes in the Angular Vestibulo-Ocular Reflex after a Single Dose of Intratympanic Gentamicin for Ménière's Disease

Meniere’s disease is an inner ear disorder that causes episodic vertigo, hearing loss, tinnitus, and fullness in the ear. The clinical disorder has been associated with hydrops, a distension of the endolymphatic fluid compartment of the inner ear. The majority of patients can successfully control their attacks of vertigo with diuretics and restriction of sodium intake. However, about 30% of patients with Meniere’s disease have intractable vertigo that does not respond to these measures. The intratympanic (middle ear) injection of gentamicin is now an alternative to ablative surgery for these patients. Gentamicin is an aminoglycoside antibiotic that is toxic to the hair cells of the inner ear, with somewhat greater vestibular toxicity than cochlear toxicity. We have treated 102 patients with unilateral Meniere’s disease with intratympanic gentamicin. Attacks of vertigo have been completely controlled in 83%, and substantially controlled (>60% reduction in frequency) in 12%. Profound hearing loss occurred as a result of treatment in only 2%, and the overall rate at which hearing declined after treatment (19%) did not differ from the expected decline in hearing with active Meniere’s disease. Recent evidence suggests that a single dose of intratympanic gentamicin can be effective in controlling vertigo in Meniere’s disease. 1 This study was undertaken to determine the effect of a single intratympanic injection of gentamicin on the function of the human angular vestibulo-ocular reflex (AVOR) in subjects with Meniere’s disease.