Normative findings of electrically evoked compound action potential measurements using the neural response telemetry of the Nucleus CI24M cochlear implant system

One hundred and forty-seven adult recipients of the Nucleus 24 cochlear implant system, from 13 different European countries, were tested using neural response telemetry to measure the electrically evoked compound action potential (ECAP), according to a standardised postoperative measurement procedure. Recordings were obtained in 96% of these subjects with this standardised procedure. The group results are presented in terms of peak amplitude and latency, slope of the amplitude growth function and ECAP threshold. The effects of aetiological factors and the duration of deafness on the ECAP were also studied. While large intersubject variability and intrasubject variability (across electrodes) were found, results fell within a consistent pattern and a normative range of peak amplitudes and latencies was established. The aetiological factors had little effect on the ECAP characteristics. However, age affected ECAP amplitude and slope of the amplitude growth function significantly; i.e., the amplitude is higher in the lowest age category (15-30 years). Principal component analysis of the ECAP thresholds shows that the thresholds across 5 electrodes can be described by two factors accounting for 92% of the total variance. The two factors represent the overall level of the threshold profiles ('shift') and their slopes across the electrode array ('tilt'). Correlation between these two factors and the same factors describing the T- and C-levels appeared to be moderate, in the range of 0.5-0.6.     

Auditory feedback does not influence random number generation: Evidence from profoundly deaf adults with cochlear implant

Oral random number generation is a widely used neuropsychological task engaging a number of overlapping neural systems of attention, number representation, response generation, and working memory. Although phonological processing is known to be essential for random number generation no information exists on the significance of the auditory feedback of hearing one's own voice on task performance. We therefore examined the influence of auditory feedback in 15 profoundly deaf adults with cochlear implants in a device-on/off experiment. No significant effects of occluding auditory feedback on random number generation were noted, thus supporting an internal response-monitoring model independent of auditory condition.     

High dose pulsatile dexamethasone therapy in children with opsoclonus-myoclonus syndrome

Opsoclonus-myoclonus syndrome (OMS) is a rare movement disorder characterized by chaotic eye movements, myoclonus, and ataxia associated with severe irritability. Different treatment modalities including steroids and cyclophosphamide have been tried in the past often with significant side effects and variable success. Here we present 11 children, diagnosed with OMS between 1999 and 2005 and treated with high dose dexamethasone pulses. Main symptoms at presentation were opsoclonus (11/11), ataxia and/or myoclonus (11/11), irritability (10/11) associated with a neuroblastoma in four children. Number of dexamethasone pulses ranged from 6 to 60 pulses. No major side effects were reported. In 6/11 children a complete and sustained remission of OMS symptoms was achieved after 6 to 29 pulses of dexamethasone. Two children from this group have a normal development and no neurological sequelae. Two further children have minor delays in fine- and gross-motor skills. Two children despite a complete recovery of OMS symptoms have persisting developmental problems. 5/11 children still require regular dexamethasone pulses in addition to daily prednisolone (n = 1) or have received cyclophosphamide pulses meanwhile (n = 2). All children continue to have developmental and neurological difficulties. In summary treatment with high dose pulsatile dexamethasone appears to be safe and beneficial in a subgroup of patients with OMS.     

Ventricular flutter in a neonate--severe electrolyte imbalance caused by urinary tract infection in the presence of urinary tract malformation

Male infants under the age of 3 months presenting with pyelonephritis in the presence of urinary tract malformation (UTM) are prone to transient pseudohypoaldosteronism. This may resemble congenital adrenal hyperplasia (CAH). Hyponatremia, hyperkalemia, dehydration, and metabolic acidosis are the primary findings that permit the diagnosis of CAH. We report a case of transient pseudohypoaldosteronism resulting from pyelonephritis and vesicouretric reflux. The 17-day-old boy presented with a salt-losing episode simulating adrenal insufficiency. An initial diagnosis of CAH was made. The severe metabolic imbalance resulted in ventricular flutter that resolved after correction of the metabolic acidosis and the electrolyte and volume depletion. Early diagnosis is essential because both conditions are potentially fatal and treatment differs significantly. Differential diagnosis may be achieved by urinalysis and abdominal ultrasound scan.     

Das Refraktärverhalten des elektrisch stimulierten Hörnervs

Introduction

Electrically evoked compound action potentials (TECAP) of the auditory nerve can be recorded in cochlear implants. TECAP thresholds are used to predict threshold levels for speech processor maps. The auditory nerve’s refractory properties can influence these levels.

Methods

Recovery functions were investigated at 84 stimulation sites in 14 patients who had Nucleus CI24 implants; neural response telemetry (NRT) and a modified forward-masking technique were used for these investigations, introducing the reference masker–probe interval (MPI).

Results and conclusion

An interval between 300 and 375 μs was found to be suitable as the reference MPI in our study. The median of the absolute refractory period was determined as 390 s and the median time constant of the recovery function, at 425 s. In practice, a reference MPI of 300 s is suggested for measurement of recovery and amplitude growth functions. As up to now the amplitude growth function has been measured at 500 s and thus mostly in a relatively refractory condition, the refractory behaviour should influence the TNRT. In addition, it was possible to explain the shape of standard forward-masking recovery functions with reference to the latency shift of the neural response.     

Clinical results of AutoNRT, a completely automatic ECAP recording system for cochlear implants

OBJECTIVE: AutoNRT is the completely automatic electrically evoked compound action potential (ECAP) measuring algorithm in the recently released Nucleus Freedom cochlear implant system. AutoNRT allows clinicians to automatically record T-NRT profiles that in turn can be used as a guide for initial fitting. The algorithm consists of a pattern recognition part that judges if the traces contain an ECAP and an intelligent flow that optimizes the measurement parameters and finds the ECAP threshold (T-NRT). The objective of this study was to determine how accurate, reliable, and fast the automatic measurements are. DESIGN: Data on more than 400 electrodes were collected as part of the multicenter clinical trial of the Nucleus Freedom cochlear implant system. T-NRT values determined by the algorithm were compared with T-NRT determinations on the same data by different human observers. Also, the time the measurements took was analyzed. RESULTS: In 90% of the cases, the absolute difference between the AutoNRT and the human observer determined T-NRT was less than 9 CL; the median absolute difference was 3 CL. A second experiment, in which a group of human observers were asked to analyze NRT data, showed high variability in T-NRT; in some cases, two experienced clinicians disagreed by more than 30 current levels. Compared with the group, AutoNRT performed as well as the "average" clinician, with the advantage that the AutoNRT threshold determinations are objective. Analysis of the timing data showed an average intraoperative measurement time of less than 20 sec per electrode with a standard deviation of 5 sec, suggesting that the total array of 22 electrodes can be measured intraoperatively in about 7 minutes on average. CONCLUSIONS: AutoNRT provides comparable accuracy to an average clinician but with the added benefit of significant time savings over manual recordings. This makes it a valuable tool for clinical measurement of ECAP threshold in cochlear implant recipients.     

Performance benefits for adults using a cochlear implant with adaptive dynamic range optimization (ADRO): a comparative study

The aim of this study was to assess the qualitative and quantitative benefits for speech-recognition ability of a preprocessing strategy known as adaptive dynamic range optimization (ADRO), used in conjunction with the subject's standard MAP, in comparison with the subject's standard MAP alone, for a group of experienced German-speaking adults using the Nucleus 24 Cochlear implant. In a prospective, single-subject, comparative study design, experienced adult CI-users were asked to trial and compare both their standard MAP and the newly fitted ADRO MAP (ADRO MAP fitting - week 0) following a take-home trial period of 5 weeks. Assessment of speech recognition ability performed in quiet (at 50, 60 and 70 dB SPL) and adaptively in noise was carried out repeatedly in two test sessions in weeks 5 and 7 (ADRO MAP postfitting) using both MAPs. The order of speech tests and MAPs tested was counterbalanced across the test sessions to control for potential learning effects during the study. Subjective assessments were performed at week 0 to assess details of current usage. Comparative subjective assessments were carried out at weeks 5 and 7 to obtain impressions of loudness of environmental sounds and speech understanding in a variety of conversational situations with both MAPs and finally MAP preference judgements. Fifteen adult, German-speaking, experienced implant users wearing their body-worn SPrint processor for a minimum of six hours and up to 16 hours per day were enrolled in the study across three university clinic hospitals in Germany. On average, speech-reception thresholds (SRT) were significantly improved with the ADRO MAP compared to using the standard MAP for all speech materials in quiet. The mean advantage for SRT values with the ADRO MAP was 2.9 dB, sigma +/- 2.8 dB (p = 0.002) for the Freiburger Numbers test and 3.3 dB, sigma +/- 3.2 dB (p = 0.008) for the Freiburger Monosyllabic Words test. In noise, the ADRO MAP led to a significant improvement for the group for the mean signal-to-noise ratio required for a 50% speech recognition score (SNR 50) for the Oldenburger sentences of 1.74 dB, sigma +/- 3.2 dB (p = 0.048). Comparison of subjective impressions of loudness of environmental sounds revealed no significant difference in the ratings observed with either MAP. For speech understanding in a variety of listening situations, 35% of subjects preferred the ADRO MAP, 29% preferred the standard MAP whereas 36% reported no difference. Statistically the MAP preferences for the groups were not significant, however a significant MAP preference was noted in four subjects for the ADRO MAP and in two subjects for the standard MAP. Our study results demonstrate significant benefits of ADRO for speech recognition ability in quiet and in noise for both soft and conversational levels of speech. For the majority of subjects, both the ADRO and standard MAPs were found to be useful on a daily basis. No reductions in performance were noted for speech recognition or loudness scaling judgements of environmental sounds when using the newly fitted ADRO MAP, suggesting a smooth transition to the use of the preprocessing algorithm. It is recommended that an ADRO MAP be provided for all CI users as an additional program option to offer potential added benefit in select environments.     

Valproic acid-induced hepatopathy: nine new fatalities in Germany from 1994 to 2003

PURPOSE: Valproic acid (VPA) is an antiepileptic drug (AED) commonly used for generalized and focal epilepsies. We provide an update on hepatotoxic side effects in Germany between 1994 and 2003. METHODS: We mailed a questionnaire to all members of the German Section of the International League Against Epilepsy, asking for VPA-induced side effects, especially severe side effects such as hepatopathy. RESULTS: As a result of our questionnaire, we found 31 cases of reversible hepatotoxicity and nine cases of lethal hepatopathies in Germany from 1994 to 2003. CONCLUSIONS: The outcome of patients with severe hepatotoxicity is better than that in the past. The risk of a VPA-induced hepatopathy is not limited to patients younger than 2 years, receiving polytherapy, or patients with congenital or acquired metabolic diseases.     

Sprachverständlichkeitsuntersuchungen bei Kochleaimplantatpatienten

The investigation of speech intelligibility under quiet and noisy conditions is essential to evaluate the auditory and verbal rehabilitation of cochlear implant patients. A set of audiological tests is introduced that has been validated and optimized by empirical investigations in adult cochlear implant users. The Kiel logatom test, the Freiburg speech intelligibility test and the adaptive measurement of speech perception threshold in noise with the Oldenburg sentence test are methods suggested for clinical use, which are also applicable for scientific investigations. The test battery provides results that can be interpreted by every professional involved in the rehabilitation process of cochlear implant patients.     

Benefits of bilateral electrical stimulation with the nucleus cochlear implant in adults: 6-month postoperative results.

OBJECTIVE: To evaluate the benefits of bilateral electrical stimulation for hearing-impaired adult subjects using the Nucleus 24 cochlear implant in a multicenter study, and to compare and quantify performance on speech perception measures in quiet and in noise and localization ability for unilateral and bilateral cochlear implant use. DESIGN:: Repeated single subject measures were carried out for each subject, with each subject serving as their own control. Assessment of unilateral and bilateral listening conditions for performance on tests of speech comprehension and sound localization were performed. Speech comprehension measures were performed in quiet at 0 degree azimuth and in the presence of background noise simultaneously presented from the same speaker and spatially separated by 90 degrees, at S+45 degrees N45 degrees and at S-45 degrees N+45 degrees . Test materials included Freiburger monosyllabic words, Oldenburger sentences, and the Hochmair-Schulz-Moser sentences. Tests of localization were performed in the horizontal plane with 12 speaker locations 30 degrees apart using a shortened sentence stimulus from the Hochmair-Schulz-Moser sentences at two possible presentation levels of 55 and 70 dB sound pressure level for assessment of directionality. The binaural advantage provided by bilateral stimulation was calculated with respect to each ear separately, classified as either the better or poorer performing ear for each speech material in quiet and in noise test conditions. For localization of sound, the binaural advantage was compared with left and right ears separately. Paired comparisons for performance data in all conditions were carried out by considering measurements for each subject in different conditions as paired observations and applying the Student's t test to determine the statistical difference between the data sets. SETTING: Tertiary referral centers with a cochlear implant program. PATIENTS: Thirty-seven profoundly hearing-impaired adults were enrolled in the study, 22 simultaneously and 15 sequentially bilaterally implanted. All patients received the Nucleus 24 cochlear implant and used the Nucleus SPrint or ESPrit 3G speech processor, with the vast majority using the ACE speech coding strategy. RESULTS: For spatially separated speech in noise conditions, an interaural performance advantage for the ear closest to the speech source (i.e., with a superior signal to noise ratio) compared with that for the ear closest to the noise source (i.e., with an inferior signal to noise ratio) is consistently demonstrated regardless of whether it is the better or poorer performing ear closest to the speech signal. This is referred to as a significant binaural head-shadow benefit, resulting in a mean improvement between -10 dB and -11.4 dB in the critical signal to noise ratio required for 50% speech comprehension for the Olden-burger sentences and a mean improvement in the maximum score of 42% to 55% for the ear closest to the speech signal over the ear farthest away for the Hochmair-Schulz-Moser sentences. Bilateral stimulation is always observed to provide a performance advantage over the unilateral listening condition for either ear when ipsilateral to the noise source. In addition, as demonstrated by approximately half the subjects tested in noise with the Hochmair-Schulz-Moser sentences, a performance advantage of bilateral stimulation may be observed over the better ear alone when positioned ipsilateral to the speech signal, which is referred to as a binaural squelch effect. On average, for the group, this resulted in a statistically significant improvement in speech comprehension scores of 8% in the bilateral listening condition compared with the scores for the better ear alone. Through assessment of comprehension of coincidental speech in noise and speech in quiet, a significant benefit of binaural redundancy was noted for the group for Oldenburger sentence scores in noise and in quiet compared with unilateral scores for either ear and for the Freiburger monosyllabic words in quiet in comparison with the better ear alone scores. Binaural stimulation also led to a significant improvement in localization ability over either monaural condition, with the root mean square degrees of error reduced by 38 degrees compared with that observed for unilateral stimulation. CONCLUSION: Similar to what has been observed for bilateral acoustic stimulation in the past, bilateral electrical stimulation provides the foundation for the potential advantages of the head-shadow effect, providing a binaural head-shadow benefit and binaural auditory processing such as binaural redundancy and binaural squelch effects, all of which combine to lead to improved speech comprehension over unilateral listening conditions. The combination of improved speech comprehension and improved localization ability made available through bilateral electrical stimulation provides the necessary foundation to further assist the hearing-impaired listener to better cope with communication in the everyday listening situation both in noise and in quiet.