Monothermal caloric test its value in assessment of vestibular function

Transcription

1 International Congress Series 1240 (2003) Monothermal caloric test its value in assessment of vestibular function Sameh A. Farid, Shereen M. El-Abd, Maha H. Abou-Elew* Abstract Background: The usefulness of either cool or warm caloric stimulation alone has been suggested as a screening tool for unilateral vestibular weakness. Previously researchers have reported falsenegative rates ranging from 0% to 52% for either cool or warm stimulation depending on variable failure criteria. Objective: To re-evaluate the monothermal caloric test before it can be routinely used in clinical settings. Methods: Data were collected retrospectively from 97 patients who had a complete electronystagmography (ENG) examination including alternate binaural bithermal caloric test (ABBT). The cut-off values of unilateral weakness (UW) for the monothermal (MT) caloric test are 27% and 30% for cool and warm stimulation, respectively. Results: There was a significant positive correlation between bithermal and monothermal unilateral weakness. Specificity of both MT caloric tests was 87.7% while sensitivity levels were 62.5% and 56.3% for cool and warm MT caloric test, respectively. The false-negative rates were correspondingly and unacceptably high for both MT caloric tests. Conclusion: There is always a substantial risk of significant vestibular pathology being missed when MT caloric test, either cool or warm, is used. D 2003 International Federation of Otorhinolaryngological Societies (IFOS). All rights reserved. Keywords: Monothermal caloric test; Electronystagmography 1. Introduction The caloric test, which is a component of the electronystagmography (ENG) battery, is regarded as the most useful method of lateralizing peripheral vestibular lesions. The most widely used type of caloric test has been the Fitzgerald and Hallpike [1] alternate binaural bithermal caloric test (ABBT) which involves irrigation of each labyrinth with warm and cool water. This technique is, however, rather time consuming (average 35 min) and somewhat uncomfortable (involving four separate * Corresponding author. address: ics@elsevier.com (M.H. Abou-Elew) / D 2003 International Federation of Otorhinolaryngological Societies (IFOS). All rights reserved. doi: /s (03)

2 1320 A.S. Farid et al. / International Congress Series 1240 (2003) irrigations) to the patient. There has been growing evidence that monothermal screening tests (MTST) can be effectively used to reduce administration time and patient discomfort but their validity must be well established before they can be used routinely in clinical situations. Several investigators have stated that warm irrigation alone is almost as sensitive as the bithermal caloric test in demonstrating vestibular abnormalities and recommended its use as a screening test. Barber et al. [2] were the first to investigate the efficacy of a monothermal warm screening test (MWST) using the ENG technique. They reported a 0.7% false-negative rate with their technique when a failure criteria of greater than 25% for ear differences and less than 11j/s for absolute slow phase eye velocities (SPV) were used with their patient sample. Although the initial report by Barber et al. [2] was encouraging, other investigators [3 9] have reported contradictory findings. Some reports indicated the false-negative rate for the MTST was acceptably low [6,7,9] while others have reported the false-negative rate was unacceptably high [3,5,8] and varied with the magnitude of monothermal asymmetry. 2. Methodology 2.1. Subjects Data were collected retrospectively from 97 patients (41 males and 56 females) ranging in age from 10 to 65 years (mean 37.7 years; S.D. 12 years) who had a complete ENG examination including the ABBT as a part from the test battery done for those complaining of vertigo or imbalance. Patients who revealed bilateral canal weakness, hyperactive response, spontaneous nystagmus or any other caloric abnormality were excluded. All testing was conducted in The Audiology and Balance Unit at Kasr Al-Aini Hospital between the years 2000 and Control data were obtained from previous work in our laboratory [10] Equipment Computerized ENG, ICS Medical Charts version 5.7, recording system was used to digitize and record eye movement data and provide a hard-copy display. A water caloric stimulator NCI-480, ICS Medical was used to deliver the water stimulus Procedures ENG testing was accomplished with horizontal electrodes near the outer canthi and vertical electrodes above and below the left eyes. Electrode impedance was always balanced and V 5000 V. A standard test battery was completed for each subject, including tests of saccade, gaze, optokinetic, and pursuit system integrity, as well as tests for spontaneous nystagmus, and the Dix-Hallpike maneuver for benign paroxysmal positional vertigo. The ABBT was

3 A.S. Farid et al. / International Congress Series 1240 (2003) conducted for all subjects with the patient in the supine position with his or her head elevated 30j. All subjects received water irrigations of 250 ml for 40 s. Testing was conducted in a darkened room with the patient s eyes closed, except during fixation suppression testing, using the following sequence: right-cool, left-cool, right-warm, and left-warm (cool = 30 jc, and warm = 44 jc). All subjects were alerted during and following each caloric irrigation. Maximum nystagmus SPV was calculated at the peak of the caloric response. Unilateral weakness (UW) and directional preponderance (DP) were calculated from the formula developed by Jonkees et al. [11]. Single temperature responses were calculated using the following formula: UW% ¼½ðR44 L44Þ=ðR44 þ L44ÞŠ 100% Similar formula was applied for cool stimulus, 30 jc. Normal limits (95% confidence limits) for UW and for DP on the ABBT are 20% and 26%, respectively. The cut-off values of UW for the monothermal (MT) caloric test are 27% and 30% for cool and warm stimulation, respectively. 3. Results To determine the level of agreement that is present between the percent asymmetry calculated from the MTST and UW on the ABBT, a Pearson product moment correlation analysis was done. The results of this analysis indicated a strong positive relationship in both cool (r = 0.69, p < 0.001) and warm (r = 0.59, p < 0.001) conditions between the two tests (see Figs. 1 and 2). These findings indicated that there is a linear relationship between the UW computed from MT cool and warm, and bithermal stimulation. However, the correlation was stronger in the cool condition. Fig. 1. Scatter plot of monothermal cool unilateral weakness (MCUW) percent as a function of bithermal unilateral weakness (BUW).

4 1322 A.S. Farid et al. / International Congress Series 1240 (2003) Fig. 2. Scatter plot of monothermal warm unilateral weakness (MWUW) percent as a function of bithermal unilateral weakness (BUW). Of the 97 ABBT included in this study, 36 were abnormal (30 cases had UW, 4 had DP, and 2 had both UW and DP directed away from the weak side). After the initial analysis, we tested the hypothesis that clinical use of the MTST would result in satisfactory delineation of patients. We used a cut-off value of 20% for the ABBT, 27% for the MCST and 30% for MWST to denote the presence or absence of UW. The results of these analyses are displayed in Tables 1 and 2. In Table 1, of 97 ENGs reviewed, the MCST identified 71% (69/97) as normal. Of these 69, 17% (12/69) were false negative (i.e. the ABBT showed UW), and 83% (57/69) had normal ABBT responses (true negatives). The use of MCST identified 28 cases having UW, 29% (8/28) were false positives (i.e. The ABBT was normal) and 71% (20/28) correctly had UW (true positives). On the other hand, in Table 2, the MWST detected 73% (71/97) as normal. Of these, 20% (14/71) were false negatives and 80% (57/71) were true negatives. There were 26 patients having UW, 31% (8/26) were false positives while 69% (18/26) were true positives, i.e. having UW on the ABBT. The sensitivity, specificity, false-negative, false-positive rates, negative and positive predictive values are computed in Table 3 for each of the MTST for predicting an abnormal ABBT. Specificity of 87.7% for both cool and warm MTST indicates that the probability of acquiring false-positive test results is not very low. The sensitivity of 62.5% versus 56.3% for the MCST versus MWST, respectively, favors administration of MCST. Table 1 Cross-tabulation of unilateral weakness, bithermal and monothermal (cool) test results Unilateral weakness (bithermal) Positive Negative Total Unilateral weakness Positive (monothermal cool) Negative Total

5 A.S. Farid et al. / International Congress Series 1240 (2003) Table 2 Cross-tabulation of unilateral weakness, bithermal and monothermal (warm) test results Unilateral weakness (bithermal) Positive Negative Total Unilateral weakness Positive (monothermal warm) Negative Total The false-negative rates were 37.5% for MCST and 43.7% for MWST, which is unacceptably high. The predictive value negative was 82.6% and 80.3% for the MCST and MWST, respectively. 4. Discussion The purpose of a screening test is to identify normal function rather than to diagnose abnormal function. In addition to specificity, a low incidence of false-negative rate is desirable since these patients would remain undetected. The objective of MTST is to decrease examination time and patient discomfort while maintaining an acceptable degree of sensitivity in detecting abnormalities as compared to ABBT. The false-positive rate is a less serious offense, as it would only require an ABBT to confirm the validity of the result. In the present study, results indicate that there is a significant positive correlation for results of ABBT and MTCT in both cool and warm stimulation. These results revealed that it may be possible to predict the presence of a vestibular UW on the basis of MTST finding alone, as suggested in the previous literature. While the specificity of MT test was 87.7% for cool and warm stimulation, the falsenegative rate was unacceptably high. The implication of telling 37.5% to 43.3% of patients who actually have a disease that they do not (a false-negative test finding) is obvious to any clinician. The results of this study were compared with the previous investigators [5,7 9] who accounted for many factors in predicting UW. Jacobson and Means [7] had a zero false-positive rate and an extremely small false-negative rate that ranged from 0% to 3% but their data were based on only 17 normal and 13 abnormal subjects. Becker [5] and Keith et al. [8] reported a high false-negative rate for both MTST and questioned its use routinely. Table 3 Operating characteristics for each of the two monothermal caloric test Operation characteristics Monothermal cool caloric (%) Specificity Sensitivity False-negative rate False-positive rate Predictive value negative Predictive value positive Monothermal warm caloric (%)

6 1324 A.S. Farid et al. / International Congress Series 1240 (2003) Recently, Jacobson et al. [9] improved the sensitivity and specificity levels for MWST by adding failure criteria other than inter-ear asymmetry. Their criteria for normalcy include SPV>11j/s, absence of abnormal ocular motility, spontaneous and positional nystagmus. With these criteria and inter-ear asymmetry of 24.5% and 29%, the sensitivity of the MWST improved to 93% and 91%, respectively. Similarly, the specificity improved to 96% and 98%, respectively. These investigators used normative data for the MWST but they did not report how these criteria were gathered, how many subjects they examined, and at which age which is also a variable that could affect. Additionally, the ocular and positional/positioning test findings should not be used to predict the outcome of caloric testing. Also, it may be difficult to get these test results on difficult-to-test population, a situation where a screening test is needed. In view of our results, we do not recommend the use of MTST in most clinical situation. Even when taking into consideration patient discomfort and time for test administration, the high possibility of a false-negative result overrides all other considerations. These characteristics may be improved with the addition of other failure criteria. We must search for other failure criteria to improve the MT caloric test results. However, a well-designed vestibular assessment protocol is advised for proper diagnosis of lateralizing vestibular lesions. In summary, we indicate that there is always a substantial risk of significant vestibular pathology being missed when MTST, either cool or warm, is used. In routine ENG testing, we recommend clinicians to avoid the use of MT caloric test as a screening measure. References [1] G. Fitzgerald, C.S. Hallpike, Studies in human vestibular function: I. Observations on directional preponderance of caloric nystagmus resulting from cerebral lesions, Brain 65 (1942) [2] H.O. Barber, G. Wright, F. Demanuele, The hot caloric test as a clinical screening device, Arch. Otolaryngol. 94 (1971) [3] V.S. Dayal, J. Farkashidy, B. Kuzn, Clinical evaluation of the hot caloric test as a screening procedure, Laryngoscope 83 (1973) [4] M.E. Norré, Evaluation of a screening procedure by hot-water caloric tests, Acta Oto-Rino-Laryngol. Belgica Tome 29 (Fasc. 4) (1975) [5] G.D. Becker, The screening value of monothermal caloric tests, Laryngoscope 89 (1979) [6] N.S. Longridge, A. Leatherdale, Caloric screening tests, J. Otolaryngol. 9 (1980) [7] G.P. Jacobson, E.D. Means, Efficacy of a monothermal warm caloric screening test, Ann. Otol. Rhinol. Laryngol. 94 (1985) [8] R.W. Keith, M.L. Pensak, B. Katbamna, Prediction of bithermal caloric response from monothermal stimulation, Otolaryngol. Head Neck Surg. 104 (1991) [9] G.P. Jacobson, J.A. Calder, V.A. Shepherd, K.A. Rupp, C.W. Newman, Reappraisal of the monothermal warm caloric screening test, Ann. Otol. Rhinol. Laryngol. 104 (1995) [10] M.H. Abou-Elew, Different caloric irrigation procedures in vestibular assessment. MD thesis, Cairo University, Faculty of Medicine, [11] L.B.W. Jonkees, J.P.M. Mass, A.J. Philipzoon, Clinical nystagmography, Pract. Otolaryngol. 24 (1962)