The vestibular implant: Opinion statement on implantation criteria for research.

This opinion statement proposes a set of candidacy criteria for vestibular implantation of adult patients with bilateral vestibulopathy (BVP) in a research setting. The criteria include disabling chronic symptoms like postural imbalance, unsteadiness of gait and/or head movement-induced oscillopsia, combined with objective signs of reduced or absent vestibular function in both ears. These signs include abnormal test results recorded during head impulses (video head impulse test or scleral coil technique), bithermal caloric testing and rotatory chair testing (sinusoidal stimulation of 0.1 Hz). Vestibular implant (VI) implantation criteria are not the same as diagnostic criteria for bilateral vestibulopathy. The major difference between VI-implantation criteria and the approved diagnostic criteria for BVP are that all included vestibular tests of semicircular canal function (head impulse test, caloric test, and rotatory chair test) need to show significant impairments of vestibular function in the implantation criteria. For this, a two-step paradigm was developed. First, at least one of the vestibular tests needs to fulfill stringent criteria, close to those for BVP. If this is applicable, then the other vestibular tests have to fulfill a second set of criteria which are less stringent than the original criteria for BVP. If the VI-implantation is intended to excite the utricle and/or saccule (otolith stimulation), responses to cervical and ocular vestibular evoked myogenic potentials must be absent in addition to the above mentioned abnormalities of semicircular canal function. Finally, requirements for safe and potentially effective stimulation should be met, including implanting patients with BVP of peripheral origin only, and assessing possible medical and psychiatric contraindications.

Effect of the stringency of conditions on caloric test results in healthy subjects. / Efecto de la rigurosidad de las condiciones sobre los resultados de la prueba calórica en sujetos sanos.

The caloric test is widely used to assess vestibular function, but the conditions in which it is performed can vary. Caloric nystagmus obtained in 57 healthy subjects were compared: 24 subjects studied in ideal conditions and 33 subjects in non-ideal conditions. A statistically significant decrease in the slow phase velocity of the 4 irrigations performed on the subjects in non-ideal conditions was observed. This must be considered, especially in subjects with suspected bilateral involvement. Stringent conditions reduce the risk of misdiagnosis with bilateral deficit.

Cervical VEMP threshold response curve in the identification of Ménière's disease.

PURPOSE: To investigate the sensitivity/specificity of a shift upward in the most sensitive frequency of the cervical vestibular evoked myogenic potential (cVEMP) threshold-response curve in the identification of Ménière's disease (MD). A secondary purpose was to investigate the clinical characteristics that had an impact on the sensitivity/specificity and to adjust the criteria for a positive shift upward in the cVEMP curve to maximize performance of the test. RESEARCH DESIGN: A retrospective review of patients diagnosed with MD and those without MD. STUDY SAMPLE: Two hundred ninety-four patients met the inclusion criteria of symptom complaints of spontaneous events of vertigo and a full vestibular and balance evaluation with cVEMP threshold-response curve testing. Two hundred six of these patients were diagnosed with MD, and 88 patients were determined to be non-MD. DATA COLLECTION AND ANALYSIS: Review of the patients' medical records was used to extract data on the results of the cVEMP curve, age, gender, duration from time of onset of spontaneous events, pure tone average from hearing test, and water caloric asymmetry. Student's t-test, χ² test, receiver operating characteristic (ROC) curve with area under the curve (AUC), Pearson correlation coefficient, and sensitivity/specificity from 2 × 2 tables were all used in the analysis. RESULTS: Basic sensitivity/specificity for a shift upward in the most sensitive frequency to 1000 Hz in the cVEMP threshold-response curve was 0.47/0.64 respectively. Clinical characteristics that were found to have a significant impact on the sensitivity/specificity were age equal to or above 60 yr and a caloric asymmetry ≥25%. Various combinations of age and caloric with the requirement of a shift upward in the cVEMP curve most sensitive frequency to 1000 Hz resulted in significant but modest improvements in sensitivity/specificity. However, the overall performance was not shown acceptable for routine clinical use with maximum sensitivity at 0.73. Therefore, placing an emphasis on specificity over sensitivity results showed specificity of 0.95 for those under 60 yr and 0.90 for those 60 yr of age or older with sensitivity at 0.20, but only in the context of a ≥25% caloric asymmetry. CONCLUSIONS: We recommend the use of the shift upward to 1000 Hz with a caloric asymmetry as the clinical protocol to maximize the use of the cVEMP threshold-response curve for assistance in the identification of MD, in the context of a ≥25% caloric asymmetry. This implies that if the test is negative no interpretation of identification of MD can be made. If the test is positive the results can be used to increase the argument for MD since the probability of the result being a false positive is only 5-10%.

The dependency of air caloric stimulus effectiveness on delivery tip characteristics.

This brief study investigates the extent and origin of the apparent dependency of air delivery speculum size on the effectiveness of air used as a stimulus in the bi-thermal caloric test, using water as a reference stimulus. Eleven normal volunteers served as subjects. Six caloric stimulus delivery conditions included air with two speculum sizes, speculum only and with a rubber tube extension, and water. The resulting nystagmus was used as an index of stimulus efficiency. The effectiveness of the air stimulus was found to be dependent on the diameter of the speculum used for air delivery. The narrower speculum generated nystagmus that was typically twice that generated by the wider speculum. Users of air caloric equipment whose design includes a speculum that influences the effectiveness of the stimulus should be aware of this dependency and ensure their clinical interpretation of results is made with reference to appropriate normative data.

Validity of the monothermal caloric testing when compared to bithermal stimulation.

BACKGROUND: the use of monothermal caloric testing as a screening tool for vestibular asymmetry has been considered as an alternative to bithermal caloric testing. AIM: to evaluate the effectiveness of monothermal stimulation when compared to bithermal stimulation in the diagnosis of labyrinth asymmetry. METHOD: the results of 389 vectoelectronystagmography, performed between 1998 and 2007, were analyzed. Monothermal stimulation at 30°C and 44°C with unilateral weakness (UW) cut-off at 20% and 25% was compared to bithermal stimulation with cut-off at 25% (gold standard). The analysis was aimed at finding which kind of monothermal caloric test (30°C or 44°C) and which kind of cut-off (20% or 25%) presented the highest specificity and sensitivity values in comparison with bithermal caloric testing. RESULTS: sensitivity and specificity of monothermal caloric tests were: 84% and 80%, at 30°C with UW at 20%; 78% and 90%, at 30°C with UW at 25%; 81% and 78%, at 44°C with UW at 20%; 76% and 85%, at 44°C with UW at 25%. CONCLUSION: monothermal caloric testing with 30°C stimulus presented the highest sensibility and specificity values in comparison to the results obtained with bithermal stimulation. However, no significant difference was observed between such values and those obtained with 44°C stimulus. In all of the analyses, monothermal testing presented low sensitivity. Thus, the abnormal result of bithermal caloric testing might be seen as normal in monothermal stimulation. The use of monothermal testing as a screening tool is better recommended for individuals whose medical history suggests a low probability of vestibular disease.

Validade da prova calórica monotermal em comparação à estimulação bitermal / Validity of the monothermal caloric testing when compared to bithermal stimulation

Background: the use of monothermal caloric testing as a screening tool for vestibular asymmetry has been considered as an alternative to bithermal caloric testing. AIM: to evaluate the effectiveness of monothermal stimulation when compared to bithermal stimulation in the diagnosis of labyrinth asymmetry. Method: the results of 389 vectoelectronystagmography, performed between 1998 and 2007, were analyzed. Monothermal stimulation at 30oC and 44ºC with unilateral weakness (UW) cut-off at 20 percent and 25 percent was compared to bithermal stimulation with cut-off at 25 percent (gold standard). The analysis was aimed at finding which kind of monothermal caloric test (30oC or 44oC) and which kind of cut-off (20 percent or 25 percent) presented the highest specificity and sensitivity values in comparison with bithermal caloric testing. Results: sensitivity and specificity of monothermal caloric tests were: 84 percent and 80 percent, at 30°C with UW at 20 percent; 78 percent and 90 percent, at 30°C with UW at 25 percent; 81 percent and 78 percent, at 44°C with UW at 20 percent; 76 percent and 85 percent, at 44°C with UW at 25 percent. Conclusion: monothermal caloric testing with 30°C stimulus presented the highest sensibility and specificity values in comparison to the results obtained with bithermal stimulation. However, no significant difference was observed between such values and those obtained with 44°C stimulus. In all of the analyses, monothermal testing presented low sensitivity. Thus, the abnormal result of bithermal caloric testing might be seen as normal in monothermal stimulation. The use of monothermal testing as a screening tool is better recommended for individuals whose medical history suggests a low probability of vestibular disease.

Tema: a estimulação calórica monotermal tem sido considerada como alternativa à prova calórica bitermal para triagem das assimetrias vestibulares. Objetivo: avaliar a confiabilidade da estimulação monotermal em relação à bitermal para o diagnóstico das assimetrias labirínticas. Método: avaliaram-se 389 resultados de vectoelectronistagmografia realizados entre 1998 e 2007. A estimulação monotermal de 30ºC e 44ºC com pontos de corte de predomínio labiríntico (PL) em 20 por cento e em 25 por cento foi comparada à bitermal com ponto de corte em 25 por cento (padrão ouro). Na análise, interessou encontrar qual foi à prova monotemal (30°C ou 44°C) e com qual ponto de corte (20 por cento ou 25 por cento) que apresentou os valores mais elevados de sensibilidade e especificidade quando comparada à prova bitermal. Resultados: a sensibilidade e especificidade da prova monotermal foram respectivamente de: 84 por cento e 80 por cento, a 30°C com PL em 20 por cento; 78 por cento e 90 por cento, a 30°C com PL em 25 por cento; 81 por cento e 78 por cento, a 44°C com PL em 20 por cento; 76 por cento e 85 por cento, a 44°C com PL em 25 por cento. Conclusão: a prova monotermal com estimulo a 30°C apresentou valores mais elevados de sensibilidade e especificidade quando comparada a bitermal. Contudo, não se observou diferença significativa em relação aos valores observados com estímulo a 44°C. Em todas as análises, a prova monotermal apresentou a limitação da baixa sensibilidade, de modo que testes alterados pela bitermal podem passar como normais pela prova monoternal. Ao se decidir pela realização da prova monotermal como triagem, deve-se realizá-la em indivíduos com menor probabilidade de estar com doença vestibular, a partir da história clínica.

Monothermal caloric screening test performance: a relative operating characteristic curve analysis.

OBJECTIVE: The objective of the present study was to evaluate the performance of the monothermal caloric screening test in a large sample of patients. DESIGN: A retrospective analysis of the medical records of 1002 consecutive patients who had undergone vestibular assessment at the Mayo Clinic during the years 1989 and 1990 was conducted. Patients with incomplete alternate binaural bithermal (ABB) caloric testing, congenital or periodic alternating nystagmus, or bilateral vestibular loss were excluded from the study. Clinical decision theory analyses (relative operating characteristic curves) were used to determine the accuracy with which the monothermal warm (MWST) and monothermal cool (MCST) caloric screening tests predicted the results of the ABB caloric test. Cumulative distributions were constructed as a function of the cutoff points for monothermal interear difference (IED) to select the cutoff point associated with any combination of true-positive and false-positive rates. RESULTS: Both MWST and MCST performed well above chance level. The test performance for the MWST was significantly better than that of the MCST for three of the four ABB gold standards. A 10% IED cutoff point for the MWST yielded a false-negative rate of either 1% (UW >or=25%) or 3% (UW >or=20%). The use of a 10% IED (UW >or=25%) for the MWST would have resulted in a 40% reduction (N = 294) in the number of ABB caloric tests performed on patients without a unilateral weakness. CONCLUSIONS: The results of this study indicated that the MWST decreases test time without sacrificing the sensitivity of the ABB caloric test.

A comparison of water and air caloric responses and their ability to distinguish between patients with normal and impaired ears.

OBJECTIVES: The caloric test is a mainstay of modern vestibular assessment. Yet caloric test methods have not been well standardized, and normal response values have not been universally agreed upon. The air caloric test has been particularly problematic. In this article, we present our efforts to establish a population-based description of the caloric response evoked by water and air stimuli at both cool and warm temperatures. DESIGN: Data were collected from a retrospective record review of patients who underwent caloric testing at Mayo Clinic Jacksonville between 2002 and 2006. Two subgroups were identified. One group was found to have no vestibulopathy after comprehensive medical investigation. The second group was found to have severe bilateral vestibular weakness; this diagnosis was based on medical evaluation and objective test results. Caloric response distributions and associated probability estimates were developed from each group. RESULTS: A total of 2587 medical records were found to contain caloric response data. Of these, 693 patients met the criteria to be classified as having no identifiable vestibulopathy (otologically normal patients with normal caloric responses). Sixty-eight patients met the criteria for bilateral vestibular weakness (reduced or absent rotatory chair responses). Our analysis yielded the following results: (1) there were differences between nystagmus distributions across stimuli. On average, the magnitude of cool water (30 degrees C) maximum slow-phase velocities was smaller than those from warm water (44 degrees C). Maximum slow-phase velocity distributions from cool (21 degrees C) and warm (51 degrees C) air stimuli were more similar to each other than were responses to water stimuli and fell between the water distributions. (2) Combined metrics (combined eye speed and total eye speed) were comparable for water and air stimuli. (3) Response distributions from otologically normal patients were different from those of patients with bilateral vestibular weakness. (4) Derived probability estimates allowed for quantification of caloric response normal limits, sensitivity, specificity, and error rates. CONCLUSIONS: Current bithermal test methods assume an equivalence of caloric response strength from warm and cool stimuli. Our results show standard cool and warm water stimuli provoke substantially different response magnitudes, with warm stimuli provoking stronger responses. When calibrated as described herein, air stimuli perform comparably with water stimuli for bithermal caloric test purposes, with more uniform and less variable response distributions. Both air- and water-based tests were able to distinguish between normal and abnormally weak ears with sensitivity and specificity values between 0.82 and 0.84. We advocate for the calibration of all caloric stimuli based on the test's statistical performance and not arbitrary assumptions about stimulus equivalence.

Water irrigation versus air insufflation: a comparison of two caloric test protocols.

The aim of the present study was to construct and compare two caloric test protocols, one for water irrigation, and one for air insufflation. A set of reference data was constructed and tabulated as well as the intersubject variability. The effect of age, sex, ear, and temperature, as well as a possible priming effect and order effect were investigated. Forty-seven subjects (18-58 years) without otological or vestibular history participated. Four response parameters were investigated: slow component velocity (SCV), frequency, unilateral weakness (UW), and directional preponderance (DP). Statistically higher SCV values were obtained for water compared to air, with statistically higher standard deviations for SCV water values. No influences of age, sex, ear, or temperature could be demonstrated on any of the response parameters. The same applied for the presence of an order effect and a priming effect. Comparing the two protocols to one another led the present authors to favour water as the standard irrigation medium, and air only in situations where water is contra-indicated.

A comparison of the monothermal and bithermal caloric tests.

This study considered whether the monothermal (MT) caloric test could predict the normality of the full conventional bithermal (BT) caloric test, and therefore be an alternative to full caloric investigation. This would have the advantages of reducing test time and patient discomfort as only two caloric tests would be needed instead of four. 744 BT caloric investigations were examined, and the unilateral weakness and directional preponderance calculated for the BT and the MT stimuli. By defining the BT results as the standard, the false-positive and false-negative results of the MT test were derived. Overall using very strict MT difference criteria of less than 5% and no spontaneous nystagmus, false-negative rates for the cool MT were very low (< 1%) and better than the warm MT (< 7.1%) suggesting that the cool MT was a reliable screen test. However, unacceptably high false-positive rates were produced reflecting more than 3/4 of normal BT results failing the MT criterion. This unacceptable false-positive rate decided against implementing the MT test at our facility. The results of this study however have guided the use of the cool air-stimulus first during BT testing and, when completion of the BT is not possible or inadvisable, satisfying the stringent MT criterion confidently indicates with a probability of > 99% the absence of an abnormal BT result.

Effects of interstimulus interval on slow phase velocity to ipsilateral warm air caloric stimulation in normal subjects.

This study investigated the effects of interstimulus interval on slow phase velocity (SPV) to ipsilateral warm air caloric stimulation in normal subjects. Results suggest that about 3 minutes should intervene between the offset of one irrigation and the onset of the second irrigation. This finding supports the hypothesis that carryover effects are likely only when nystagmus from the preceding irrigation overlaps the subsequent irrigation. If correct, clinicians do not have to wait a fixed time period between stimuli, but can initiate caloric stimulation as soon as nystagmus has ceased from the preceding irrigation. This recommendation compensates for individual and procedural differences. Test-retest reliability also was investigated. Findings suggest that when immediate test-retest differences exceed approximately 6 degrees/second (95% confidence interval), the examiner should administer additional trials until stability is ascertained. Moreover, unusual or significant findings should be verified with repeat testing.