Measuring caloric response: comparison of different analysis techniques

INTRODUCTION

Electronystagmography (ENG) testing has been supplanted by newer techniques of measuring eye movement with infrared cameras (VNG). Most techniques of quantifying caloric induced nystagmus measure the slow phase velocity in some manner. Although our analysis is carried out by very experienced assessors, some systems have computer algorithms that have been "taught" to locate and quantify maximum responses. We wondered what differences in measurement might show up when measuring calorics using different techniques and systems, the relevance of this being that if there was a change in slow phase velocity between ENG and VNG testing when measuring caloric response, then normative data would have to be changed. There are also some subjective but important aspects of ENG interpretation which comment on the nature of the response (e.g. responses which might be "sporadic" or "scant").

METHODS

Our experiment compared caloric responses in 100 patients analyzed four different ways. Each caloric was analyzed by our old ENG system, our new VNG system, an inexperienced assessor and the computer algorithm, and data was compared.

CONCLUSIONS

All four systems made similar measurements but our inexperienced assessor failed to recognize responses as sporadic or scant, and we feel this is a limitation to be kept in mind in the rural setting, as it is an important aspect of assessment in complex patients. Assessment of complex VNGs should be left to an experienced assessor.

Visual Vestibular Mismatch in Work-Related Vestibular Injury

OBJECTIVE

To define and investigate the symptom set known as visual-vestibular mismatch and analyze its nature and occurrence in two groups of patients referred for dizziness.

STUDY DESIGN

Prospective study of two groups of sequentially referred patients complaining of dizziness, imbalance, or both.

SETTING

A tertiary and quaternary care ambulatory referral center.

PATIENTS

Two groups of patients were studied. One was a group of patients who had suffered work-related head trauma and had subsequent complaints of dizziness and/or imbalance. The other was a group of patients referred for dizziness and/or imbalance who had no history of head trauma, work-related injury, or litigation procedures.

INTERVENTIONS

Standard vestibular assessment including computerized dynamic posturography was carried out on all patients. A series of questions was designed to quantify patients' complaints of symptoms of visual-vestibular mismatch, and patients were scored according to their yes/no answers to the five questions.

MAIN OUTCOME MEASURES

Results of traditional vestibular tests were correlated with the answers to the questions. Computerized dynamic posturography and electronystagmography results were compared between both symptomatic and nonsymptomatic patients and also between patients who had traumatic and nontraumatic causes of their symptoms.

RESULTS

We found no correlation between test results and the presence of visual-vestibular mismatch symptomatology. There does seem to be a connection between the presence of motion sickness symptomatology and the development of visual-vestibular mismatch symptoms.

CONCLUSION

Although visual-vestibular mismatch is of vestibular origin, it is discernible only after obtaining a careful history. It is a genuine symptom set of vestibular origin, and there is a certain group of patients who are more sensitive to this symptom set and who are often debilitated by its presence.

A New Set of Criteria for Evaluating Malingering in Work-Related Vestibular Injury

OBJECTIVE

To develop and use a set of criteria using computerized dynamic posturography results to detect aphysiologic behavior in patients with complaints of imbalance, and to compare the efficacy of this system with present quantitative techniques and with subjective methods of evaluating malingerers.

STUDY DESIGN

Prospective study of two groups of sequentially referred patients complaining of dizziness and/or imbalance.

SETTING

A tertiary and quaternary care ambulatory referral center.

PATIENTS

Two groups of patients were studied. One was a group of patients who had suffered work-related head trauma and had subsequent complaints of dizziness and/or imbalance. The other was a group of patients referred for dizziness and/or imbalance who had no history of head trauma, work-related injury, or litigation procedures.

INTERVENTIONS

Standard vestibular assessment including computerized dynamic posturography was carried out on all patients.

MAIN OUTCOME MEASURES

All patients in both groups were scored for aphysiologic behavior using a quantified formula that has been used to detect malingerers, an analysis criterion using different aspects of computerized dynamic posturography performance that has been used for some time, and our newly developed nine-point scoring method. Results of all three methods were compared to determine the effectiveness of each one in detecting malingering behavior.

RESULTS

Our nine-point protocol was effective in assessing patients in a consistent manner. Assessment using the quantitative formula in the literature raised suspicions of malingering in many patients with no known ulterior motives, some of whom had documented vestibular disease. Our criteria also evaluate other aspects of performance not evaluated by the presently used techniques.

CONCLUSION

Our newly developed criteria are effective at evaluating the medicolegal patients from both the quantitative and qualitative viewpoints, and provide a more thorough assessment than has previously been available.

“Across the Board” Posturography Abnormalities in Vestibular Injury

OBJECTIVE

To analyze a newly defined group of Computerized Dynamic Posturography abnormalities and to determine if these patients' abnormalities are of vestibular origin.

STUDY DESIGN

Analysis of results drawn from our larger study of two groups of sequentially referred patients complaining of dizziness and/or imbalance.

SETTING

A tertiary and quaternary care ambulatory referral centre.

PATIENTS

Two groups of patients were studied. One was a group of patients who had suffered work-related head trauma and had subsequent complaints of dizziness and/or imbalance. The other was a group of patients referred for dizziness and/or imbalance who had no history of head trauma, work related injury. or litigation procedures.

INTERVENTIONS

Standard vestibular assessment including Computerized Dynamic Posturography was carried out on all patients.

MAIN OUTCOME MEASURES

CDP results of all patients were reanalyzed and all results were pulled which were abnormal on at least 5 of 6 sensory conditions. All results were analyzed using a quantitative method of detecting malingering and also using our newly developed nine point subjective/objective criteria scale.

RESULTS

While the standardized formulae categorized most of these results as "aphysiologic," our nine-point protocol showed most of the patients to be legitimate.

CONCLUSIONS

These results represent a legitimate subgroup of vestibular patients that we feel have been more or less unrecognized, many of whom are incapacitated by imbalance and disorientation. These results also are helpful in measuring safety of these patients in the workplace.

Caloric response does not decline with age

Complaints of imbalance in the elderly are commonly heard by clinicians, and pathology of the vestibular system may play an important role in these complaints. While there is solid anatomical evidence for age related decline of some vestibular structures, a corresponding deterioration in physiologic function has not been convincingly demonstrated. Vestibular function is traditionally measured with caloric irrigations. Although there has been some age dependent change in caloric response shown, there is no good parallel between caloric response and imbalance in the elderly patient. Our experiment confirms that slow phase velocity of caloric responses does not decline with age. Calorics measure only one part of the vestibular system, and so should not be regarded as representative of balance system function. As a result, measured caloric response does not parallel documented anatomic age-related decline of the vestibular system.

Effects of dimenhydrinate on computerized dynamic posturography

OBJECTIVE

Previous studies have demonstrated that sedatives and antiemetics commonly used by patients suppress the vestibulo-ocular reflexes during electronystagmography, making it more difficult to quantify function in such patients. The effects of these medications on computerized dynamic posturography (CDP) have not been studied, and the influences, if any, on the vestibulospinal reflexes are not known. We aimed to study the influence, if any, of dimenhydrinate on CDP performance.

DESIGN

A double-blinded study using a randomized protocol to compare the effects of dimenhydrinate and placebo on CDP performance in normal subjects.

SETTING

A tertiary/quaternary care facility using a standardized CDP assessment protocol.

METHODS

After a CDP training session (one assessment) to rule out any learning effect, 10 subjects underwent CDP assessment on 2 separate days after ingestion of either a standard single dose of dimenhydrinate or placebo.

MAIN OUTCOME MEASURES

Pre- and post-medication CDP performance was measured using Sensory Organization Test (SOT) composite scores and also scores on CDP conditions particularly sensitive to measurement of vestibular impairment (SOT conditions 5 and 6).

RESULTS

Analysis of data showed no significant effect on CDP performance of normal subjects after dimenhydrinate administration, although there may be a trend toward a slight effect on performance.

CONCLUSIONS

There seems to be no significant effect of dimenhydrinate on CDP performance in normal subjects, although there may be a trend. Further studies using a dose causing more significant symptoms or using a higher number of subjects may clarify this.

Low-dose intratympanic gentamicin treatment for dizziness in Ménière's disease

OBJECTIVE

Intratympanic gentamicin is used to control dizziness of Ménière's disease, with a low rate of morbidity and a high success rate. We aimed to develop a new technique and schedule of therapy using a lower dose.

DESIGN

A retrospective chart review in Ménière's disease patients treated for intractable dizziness.

SETTING

A tertiary/quaternary care outpatient setting.

METHODS

Patients were administered intratympanic gentamicin using a low-dose protocol on 2 successive days and evaluated with pre- and post-treatment audiovestibular assessment.

MAIN OUTCOME MEASURES

Standard evaluation methods of audiovestibular function measured pre- and postfunction of hearing and balance to determine the effects of treatment and morbidity in the form of hearing loss. A telephone follow-up survey was also undertaken.

RESULTS

Patients reported satisfactory control of dizziness, with little morbidity in the form of hearing loss. We also found that the use of a myringotomy tube could be precluded. Post-treatment symptoms of imbalance reported by patients settled as patients compensated. In a telephone survey conducted some years after treatment, patient satisfaction was found to be high.

CONCLUSIONS

This two-dose regime was shown to be effective in controlling dizzy spells. In patients refractory to the initial two-dose treatment, a follow-up course of treatment usually proved effective. Long-term follow-up of patients seems to show that failure of treatment usually occurs within the first few months, and that symptoms, once controlled, rarely recur.

Dizziness from whiplash and head injury: differences between whiplash and head injury

OBJECTIVE

Large discrepancies exist in the literature regarding incidence and types of symptomatology in whiplash. This is because of the evolution of whiplash injury over the years with the advent of head rests and seat belts. Previous authors have regarded symptoms of dizziness as a result of brainstem or cerebellar injury or both. It has been difficult in those studies to ascribe a mechanism of injury, as patients with whiplash injury only have been grouped with those who have incurred mild traumatic brain injury as a result of a significant blow to the head. The authors saw the need to delineate patients who had suffered whiplash injury from those who also had suffered mild head injury, as defined in the rehabilitation-neurosurgical literature, to attempt to define differences in symptoms, abnormalities, and mechanisms of recovery in these two groups.

STUDY DESIGN

The study design was a retrospective case review.

SETTING

The study was conducted at a tertiary-quaternary referral clinic.

PATIENTS

The records of 36 patients were reviewed. Nineteen of these patients suffered a whiplash-associated disorder and 17 suffered a mild head injury as well. These patients were referred for assessment of symptoms persisting for at least 2 years after their injury. Patients were excluded if they had not completed clinical assessment, including electronystagmography (ENG) and computerized dynamic posturography (CDP).

INTERVENTIONS

A full history, otolaryngologic examination, including assessment of eye movements, corneal reflexes and gait, as well as an investigation, including ENG and CDP, and history taking and detailed recording of related complaints immediately before diagnostic work-up were performed.

MAIN OUTCOME MEASURES

Symptoms reported by patients who had received either whiplash alone or whiplash plus mild head trauma as defined in the literature were measured. Patients were classified according to type of accident, type of injury suffered, and degree and nature of posturographic abnormalities.

RESULTS

Patients often have similar complaints regardless of whether or not they had suffered a head injury. Although CDP showed abnormalities in both groups, standard ENG assessment, including caloric testing, showed abnormalities only in the head-injured group. The posturographic abnormalities also were analyzed in both groups, and it was found that there was a correlation between the type of posturographic abnormality and the type of injury suffered. Although ENG testing is done routinely, posturography is shown to be more sensitive in picking up abnormalities. In addition, the authors have shown that posturography can delineate the type of injury suffered by exhibiting the compensation strategy used as well as the efficacy of that compensation strategy.

CONCLUSIONS

Because ENG abnormalities are limited to patients who have suffered a head injury, the inference is that these two groups of patients have suffered damage at different sites along the balance system pathways, but both of these lesions can lead to similar symptoms. Although the mechanisms of whiplash injury and how they affect the vestibular system are poorly understood, posturography testing is essential in inferring how a patient is recovering by measuring how and how well the patient is overcoming his or her deficit. This has important medical legal implications regarding legitimizing a patient's problem, prognostic factors, as well as rehabilitation plans, measures, and outcomes.

Specific vocalized complaints in whiplash and minor head injury patients

OBJECTIVE

Subtle complaints of visual-vestibular mismatch may not be elicited in an initial history-taking. Clinicians must be familiar with the nature of these complaints when assessing whiplash patients because other injuries may predominate and patients do not volunteer these more subtle complaints, which may be persisting and sometimes debilitating.

STUDY DESIGN

A retrospective case review was performed.

SETTING

The study was conducted at a tertiary/quaternary referral clinic.

PATIENTS

Patients with whiplash, mild head injury, or both were referred for assessment of symptoms persisting for at least 2 years after their injury.

INTERVENTIONS

A full history; otolaryngologic examination; including assessment of eye movements, corneal reflexes, and gait; investigation including electronystagmography and computerized dynamic posturography; and history-taking and detailed recording of related complaints were performed immediately before diagnostic workup.

MAIN OUTCOME MEASURES

Many patients had more subtle complaints, which we now recognize as indicative of vestibular pathology, that have not previously been described in detail in the literature and are often generalized using terms such as "dizziness" or "lightheadedness." It is important to take a detailed history from these patients to delineate their more subtle complaints, because their symptoms frequently do not "fit" into traditional syndromes.

RESULTS

Complaints verbalized by patients were tabulated. On more careful analysis, they can be identified as arising from a mismatch between vestibular information and other sensory information used to maintain balance.

CONCLUSIONS

Many patients with the standard vestibular syndromes have the same subtle complaints (apart from the standard vertiginous complaints) that patients with whiplash and minor head injury verbalize. The similarity of the complaints in the two groups indicate that the subtle symptoms are caused by underlying vestibular disease.

Training effects during repeated therapy sessions of balance training using visual feedback

Visual biofeedback of postural sway is currently being investigated as a therapeutic technique to reduce postural instability in selected patient populations. Before the efficacy of this type of therapy can be determined in a clinical setting, the performance curves of a normal population doing the static and dynamic balance training exercises have to be delineated. Two groups of normal subjects were evaluated during a daily and weekly protocol of dynamic balance exercises using visual feedback of their center of gravity (COG) and theoretical limits of stability. Static stability in a central position was measured with eyes open, eyes closed, and with visual feedback of the COG in a pre-therapy to post-therapy assessment. No significant change was observed in any of these variables from the pre-therapy to the post-therapy evaluation; as well there was no difference between the scores of both groups. Dynamic variables were evaluated in both a pre-therapy to post-therapy assessment, and over the course of therapy. Each of these protocols required the subjects to track targets representing 75% of their limits of stability on a computer screen with their COG. The time taken and the accuracy to move the COG cursor from target to target, as well as the body sway upon reaching the target were evaluated. Transition time and sway area both decreased significantly (p less than 0.01) from the pre-therapy to the post-therapy assessment for both groups, with path error decreasing significantly for the daily therapy group only. No significant difference was demonstrated between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

The Dynamic Illegible E-test: A Technique for Assessing the Vestibulo-ocular Reflex

The Dynamic Illegible E (DIE) test measures visual acuity with head held still while reading a specially designed visual acuity chart of E's. The head is then moved passively and the change in visual acuity is recorded. The DIE test has previously been shown to be very useful for assessing patients with aminoglycoside ototoxicity. In the present study, statistical analysis using multiple regression showed that the degree of abnormality in the DIE test during horizontal and vertical head movement was correlated with the degree of caloric reduction. Ridit analysis allows comparison between a number of naturally ordered categories. The ridit analysis showed significant differences between groups of patients with varying degrees of caloric reduction. There was also a significant difference in DIE test scores between a group of normals with no history of otoneurological complaint and an age- and sex-matched population of dizzy patients with normal caloric results. As none of our 110 normal patients had more than a one row drop while reading the DIE test with head moving, we feel that it is safe to regard a drop of more than two rows with head moving as abnormal. Perhaps even a mild caloric reduction represents relatively severe vestibular damage and the DIE test has the potential to delineate some patients who have no caloric reduction.

The dynamic illegible E-test. A technique for assessing the vestibulo-ocular reflex

The Dynamic Illegible E (DIE) test measures visual acuity with head held still while reading a specially designed visual acuity chart of E's. The head is then moved passively and the change in visual acuity is recorded. The DIE test has previously been shown to be very useful for assessing patients with aminoglycoside ototoxicity. In the present study, statistical analysis using multiple regression showed that the degree of abnormality in the DIE test during horizontal and vertical head movement was correlated with the degree of caloric reduction. Ridit analysis allows comparison between a number of naturally ordered categories. The ridit analysis showed significant differences between groups of patients with varying degrees of caloric reduction. There was also a significant difference in DIE test scores between a group of normals with no history of otoneurological complaint and an age- and sex-matched population of dizzy patients with normal caloric results. As none of our 110 normal patients had more than a one row drop while reading the DIE test with head moving, we feel that it is safe to regard a drop of more than two rows with head moving as abnormal. Perhaps even a mild caloric reduction represents relatively severe vestibular damage and the DIE test has the potential to delineate some patients who have no caloric reduction.

The dynamic illegible E (DIE) test: a simple technique for assessing the ability of the vestibulo-ocular reflex to overcome vestibular pathology

Vestibulo-ocular reflex (VOR) compensation, shown by the Dynamic Illegible E test (DIE test), for vestibular damage (as shown by caloric reduction) did not coincide consistently with time from initial onset of vestibular disease. We theorize that the reason for this is the variable efficiency of different compensatory mechanisms used by individuals in overcoming vestibular pathology. Methods of compensation are discussed in detail. The DIE test measures the efficiency of the VOR by comparing visual acuity with head still and head moving. While many patients compensated satisfactorily for vestibular injury to the point where they were able to function adequately, other patients appeared not to compensate. There was no obvious prior indication of which patients would compensate well. There was a suggestion that younger patients did better, but neither duration of symptoms nor severity of pathology appeared to be factors in the ability to compensate. Although younger patients may fare better as a group, there are no predictive criteria for the amount or rate of recovery which an individual patient with vestibular pathology will make.

Machado-Joseph disease: the vestibular presentation

Three patients presented with Machado-Joseph disease. We documented the vestibular abnormalities characteristic of Machado-Joseph disease during clinical examination. Electronystagmographic (ENG) abnormalities included bilateral gaze nystagmus, saccadic pursuit and failure of fixation suppression suggestive of cerebellar-brainstem pathology. Machado-Joseph disease is a degenerative neurological condition, inherited in an autosomal dominant fashion. It occurs in patients of Portuguese Azorean extraction. We suggest that otolaryngologists with a referral base including a Portuguese community be familiar with this disease as it may present in its early stages with symptoms of non-specific imbalance.

Arnold-Chiari malformation and the otolaryngologist: place of magnetic resonance imaging and electronystagmography

The Arnold-Chiari malformation (ACM) is a rare congenital condition in which there is a downward displacement of the cerebellum through the foramen magnum. Patients with this condition frequently develop symptoms of ataxia, imbalance, or vertigo. As a result the patient is often referred to an otolaryngologist. Such a case is reported. A patient presented with imbalance, had downbeating nystagmus on down gaze, and had other eye movement abnormalities recorded on electronystagmography (ENG) which were strongly suggestive of central pathology. Although her computerized tomography (CT) scan was normal, the eye findings and neurological evaluation were strongly suggestive of an ACM. A repeat CT scan with intrathecal metrizamide was abnormal. A definite diagnosis of ACM was confirmed using the new investigative technique of magnetic resonance imaging (MRI).

A discussion of the dynamic illegible "E" test: a new method of screening for aminoglycoside vestibulotoxicity

Although aminoglycoside antibiotics have been successful in controlling infections, the side effects of these drugs include vestibulotoxicity that can be irreversible. In a patient with intact visual and proprioceptive systems, the effects can be compensated for, but in a patient with impairment of one of these systems, loss of vestibular function can be devastating. There is little if any agreement in the literature about how to monitor patients undergoing therapy with these drugs. A reading test is described. It uses the ability of the vestibulo-ocular reflex to stabilize an image during head movement. The test is quantified using change in visual acuity with head movement to monitor damage to the vestibular system. Patients with loss of vestibular function are incapable of performing the test. Some evidence points to the test being more sensitive than standard caloric irrigations. We propose that it be used to monitor patients receiving aminoglycoside antibiotics.

Vestibular studies in Pelizaeus-Merzbacher disease

Pelizaeus-Merzbacher disease is a rare sex-linked recessive neurological disorder. It presents with a slowly progressive neurological deterioration. It is liable to be misdiagnosed as cerebral palsy. A family history of similar disease is a clue to the diagnosis. A patient with this condition has been followed over many years. Nystagmus was noted to be present shortly after birth. Audiovestibular investigations were performed. All tests of peripheral hearing were normal. ABR indicated abnormal brainstem conduction. Several electronystagmographic abnormalities were present. These were of a central type. They included failure of fixation suppression, poor smooth pursuit, and impaired performance of optokinetic nystagmus at high stripe speeds. During caloric-induced nystagmus an excessively prolonged slow phase of nystagmus with wide eye excursions was seen. We have not seen this feature in any other diseases and we suggest it may be specific for this syndrome.