The effects of posteroventral pallidotomy on balance function in patients with Parkinson's disease.

Parkinson's disease is a chronic, progressive neurodegenerative disorder resulting from dopaminergic cell loss in the pars compacta of the substantia nigra. Conventional treatment of Parkinson's disease consists of pharmacological replacement of dopamine. A treatment alternative, posteroventral pallidotomy (PVP), has been used for medically intractable stages of the disease. The purpose of this study was to evaluate the effects of PVP on balance function, as measured by dynamic posturography, in patients with medically intractable Parkinson's disease. Five subjects were studied within 2 days prior to and within 6 months following PVP. Pretreatment abnormalities were found in vestibular, visual, and somatosensory processing in balance function. Posteroventral pallidotomy resulted in improvement in vestibular compensation of posture in some patients, which may be at least partially due to an improvement in latencies to respond to changes in stance. Dynamic posturography is an effective tool in the evaluation of balance and posture in patients with advanced Parkinson's disease.

Auditory disorder in central nervous system miliary tuberculosis: case report.

We evaluated a 28-year-old female with a unilateral hearing loss of unusual pathogenesis, that of central nervous system miliary tuberculosis. Audiologic and otologic findings were consistent with left retrocochlear disorder, characterized by a profound hearing sensitivity loss, absent acoustic reflexes, normal otoacoustic emissions, and the presence of only wave I of the auditory brainstem response. Imaging studies revealed the presence of multiple punctate lesions, one of which was extra-axial and located at the left cerebellopontine angle. The pattern of audiometric test results, particularly the combination of normal otoacoustic emissions and profound hearing sensitivity loss, contributed importantly to the investigative sequence leading to the final diagnosis.

A double-blind placebo-controlled trial of baclofen in the treatment of tinnitus.

OBJECTIVE: To determine the effectiveness of baclofen in ameliorating tinnitus in adult patients. STUDY DESIGN: Randomized double-blind placebo-controlled trial. SETTING: California Ear Institute at Stanford, California, a tertiary otology/neurotology referral center. PATIENTS: Restricted to adults receiving otologic evaluation at the California Ear Institute at Stanford. Some patients had a primary complaint of tinnitus, whereas others with tinnitus were recruited during treatment for another condition. The study population was felt to be representative of the general population with tinnitus. INTERVENTIONS: Three weeks of baclofen (10 mg orally twice daily for 1 week, 20 mg orally twice daily for the second week, and 30 mg orally twice daily for the third week) or placebo designed to mimic baclofen capsules in route, schedule, appearance, and taste were given to patients. MAIN OUTCOME MEASURES: Tinnitus handicap inventory, pitch and loudness matching, and maskability of tinnitus. RESULTS: Subjective and objective evaluation failed to demonstrate any clinical or statistical advantage of baclofen over placebo. Reports of subjective improvement occurred in only 9.7% of the baclofen versus 3.4% of the placebo groups, a nonsignificant difference. Withdrawal from the baclofen arm of the study occurred in 26% due to side effects, which could be attributed to the medication. CONCLUSIONS: Baclofen is no more effective than placebo in ameliorating tinnitus in adult patients.

Hearing aids. I. Conventional hearing devices.

State-of-the-art hearing aids incorporate advances in signal processing, miniaturization, and programmability. This technological progress has been accompanied by parallel enhancements in evaluating and fitting strategies. In addition, in the past several years, knowledge has increased about the influences of amplification on hearing ability and about the influences of hearing ability on benefit from amplification.

Improving the efficiency of speech audiometry: computer-based approach.

Speech audiometric measures were carried out on 981 patients using a computer-based system that permitted a comparison between two modes of signal presentation, manual and automatic. The manual mode, designed to simulate the pace of live-voice testing, allowed the presentation of speech signals at a rate dictated by the patient's response. The automatic mode, designed to simulate tape-player testing, fixed the interstimulus interval. A comparison of elapsed time for the completion of word recognition testing with phonetically balanced (PB) word lists showed that use of the manual mode resulted in increased efficiency. Testing time was reduced by an average of 22 percent. These results suggest that the clinical efficiency of speech audiometric testing can be enhanced by using a computer-based manual approach. The combination of digitally recorded speech stimuli with a computer-based manual approach may provide a useful compromise between the efficiency of live-voice testing and the signal consistency of magnetic-tape or compact-disc recordings.

Auditory evoked potentials in Rett syndrome.

This study was designed to assess auditory function in subjects with Rett syndrome, a rare neurologic disorder that is characterized by progressive symptoms of dementia, ataxia, respiratory disorder, and communication disorder. Auditory evoked potentials, including the auditory brainstem response (ABR), middle latency response (MLR), and late vertex response (LVR), were recorded in 36 subjects with Rett syndrome. Results showed a systematic decline in auditory function from the peripheral to the central auditory system, with normal ABR in all subjects, normal MLR in 50 percent of subjects, and normal LVR in 36 percent of subjects. Results suggest that hearing sensitivity and the functional integrity of eighth nerve and auditory brainstem pathways are not affected in subjects with Rett syndrome. However, abnormality of both the MLR and LVR suggest the presence of central auditory disorder.

Sudden hearing loss in multiple sclerosis: case report.

This case illustrates the occurrence of a sudden hearing sensitivity loss that, in all likelihood, was the result of brainstem disorder resulting from multiple sclerosis (MS). Subject LD is a young woman who developed a sudden hearing loss while hospitalized for exacerbation of symptoms related to multiple sclerosis. By her own report, she had normal hearing in her left ear at the time of hospitalization. Four days after admission, she developed a hearing loss in her left ear, accompanied by roaring tinnitus and fullness. An audiologic evaluation revealed a substantial high-frequency sensitivity loss in the left ear. The combination of absent acoustic reflexes, depressed speech understanding, abnormal Bekesy audiometry, and an abnormal auditory brainstem response (ABR) was consistent with brainstem site of disorder. Over the next 2 weeks, hearing sensitivity recovered to within normal limits. This change in hearing sensitivity coincided with the recovery of acoustic reflexes, improvement in speech understanding, and partial recovery of the ABR.

Otoacoustic emissions as a cross-check in pediatric hearing assessment: case report.

Audiologic assessment of infants and young children can be confounded by neurologic disorders or neuromaturational delays. In some cases, this results in an inability to assess hearing sensitivity by behavioral measures or by auditory evoked potentials. This case illustrates such an audiologic challenge. Subject DF was born with hydrocephaly, which was treated with repeated shunt surgeries and resulted in seizures and pervasive developmental delays. At 9 months of age, the child was tested by auditory brainstem response (ABR) measurement and found to have no response to sound. Believing that her child had hearing, DF's mother sought a second opinion. Results of an audiologic evaluation at 11 months of age showed no measurable behavioral responses in the sound field and an ABR abnormality that prevented prediction of hearing sensitivity. In contrast, sensitivity prediction by the acoustic reflex and results of both transient-evoked and distortion-product otoacoustic emissions predicted normal peripheral hearing sensitivity. This case illustrates the usefulness of otoacoustic emissions as an additional cross-check measure in pediatric hearing assessment.

Cyclic steroid replacement alters auditory brainstem responses in young women with premature ovarian failure.

To determine the independent contributions of estradiol and progesterone to the auditory brainstem response (ABR) latency changes associated with the menstrual cycle, we obtained ABRs on young women with premature ovarian failure who were undergoing cyclic hormone replacement therapy (HRT). We evaluated the influence of cyclic HRT on the ABRs of young women in three controlled phases of the same replacement cycles: 1) no steroid replacement, 2) estrogen-only replacement (E2-only), and 3) estrogen-plus-progesterone replacement (E2-plus-P). A significantly lengthening of wave V peak latency and I-V interpeak interval was found during E2-only replacement. Despite equivalent circulating estradiol levels, both wave V peak latencies and wave I-V interpeak intervals significantly decreased during the E2-plus-P replacement phase as compared to the E2-only replacement phase. These findings are compatible with the hypothesis that estradiol potentiates secretion of the inhibitory neurotransmitter gamma-amino-butyric acid (GABA) at auditory nerve synapses, leading to delayed synaptic conduction time. Progesterone is known to blunt E2-potentiated GABA release and may antagonize its prolongation of wave V latency.

Estrogen influences auditory brainstem responses during the normal menstrual cycle.

We evaluated the impact of the menstrual cycle on auditory brainstem response (ABR) latency in nine normally cycling women. Subjects (age 23-40 years) using no hormonal therapy were recruited and underwent ABR testing during four different phases of the same menstrual cycle: early follicular (cycle days 1 to 3); mid-cycle (cycle days 12 to 15); mid-luteal (cycle days 17 to 22), and premenstrual (cycle days 25-27). Cycles were verified by basal body temperature, and serum estrogen (E2), progesterone (P), and gonadotropin levels. A control group of nine women (age 23-40 years) on oral contraceptives (Nordette-28) was also studied four times during a pill cycle. Results show a significant increase in the latency of wave III and wave V peak latencies and in the I-V interpeak interval associated with a high estrogen state at the mid-cycle phase. No statistically significant variations in latency were found in the birth control pill group. These data suggest the existence of brainstem auditory neural pathways that are sensitive to fluctuations in E2 levels during the menstrual cycle.

Special hearing aid considerations in elderly patients with auditory processing disorders.

Elderly individuals often have more deficits in speech understanding than would be expected in younger individuals with the same degree of hearing loss. Such deficits may be attributed to the complex nature of age-related changes that occur throughout the central auditory nervous system and are generally referred to as auditory processing disorders. These deficits have been related to poorer performance with hearing aids, reduced satisfaction with hearing aids, and reduced prognosis for successful benefit from hearing aid use. Intervention strategies that enhance signal to noise ratio are often successful in overcoming the debilitating effects of auditory processing disorder in the elderly.

The prevalence of central presbyacusis in a clinical population.

To evaluate the prevalence of central auditory disorder as a function of aging, we analyzed speech audiometric test results on 700 patients, 100 patients from each of seven half-decades beginning at age 50 years. In addition, we evaluated the extent to which prevalence estimates could be explained by the effect of hearing loss on measures of central auditory processing and the difference in prevalence of central presbyacusis between a clinical sample and a nonclinical sample. Results showed that the prevalence of central presbyacusis increased with age and that the highest prevalence was a striking 95 percent in the 80+ year age group. Results also showed that, even when degree of hearing loss and ability to perform the speech audiometric task were equated, the prevalence of central presbyacusis increased systematically with age. Finally, results showed that the prevalence was lower in the nonclinical sample than in the clinical sample at all ages, but that a substantial amount of central presbyacusis existed in the nonclinical subjects, especially in the oldest age groups.

The acoustic reflex in diagnostic audiology: from Metz to present.

In 1946, Metz described what was probably the first practical impedance bridge for measurement of the acoustic reflex. Over the next four decades, diagnostic use of the acoustic reflex progressed in parallel with instrumentation refinements. Today, acoustic reflex threshold and decay testing are a routine component of the diagnostic audiology test battery. Recent advances in the measurement of suprathreshold latency and amplitude have further enhanced the diagnostic value of acoustic reflex measurement.

Abnormalities of the acoustic reflex in multiple sclerosis.

Acoustic reflect morphology was examined in 122 patients with a diagnosis of definite multiple sclerosis. Abnormality in some dimension of acoustic reflex morphology was observed in 75 per cent of the study population. The most commonly observed abnormality was an alteration in one or more of the three relative amplitude indices (afferent, efferent, or central pathway index). Other abnormalities included delayed onset latency, delayed offset latency, reduction in absolute amplitude, and threshold elevation.

Central presbyacusis: a longitudinal case study.

An elderly patient with presbyacusis was tested on four occasions over a 9-year interval. Although there was little change in peripheral hearing sensitivity, central auditory function declined substantially. Diminished success as a hearing aid user seemed to parallel the change in central function. Results suggest that the central changes were auditory-specific rather than generalized cognitive in origin.

Identification of stapedius muscle motoneurons in squirrel monkey and bush baby.

The location of brainstem neurons which mediate the stapedius reflex was identified by injecting horseradish peroxidase into the stapedius muscle of squirrel monkeys and bush babies. Retrogradely labeled neurons, arranged in a one- to three-cell column, were found medial to the main facial motor nucleus in squirrel monkeys and ventral to it in bush babies. Nissl, protargol, and acetylcholinesterase stains were subsequently used to identify and describe this unique column of cells. It was found that staining characteristics, as well as shape, size, and location, distinguish stapedius muscle motoneurons from closely associated cell groups. Furthermore, stapedius muscle motoneurons are morphologically similar to periolivary cells and morphologically dissimilar to cells within the facial motor nucleus.

Acoustic reflex averaging.

Signal averaging techniques have been applied to acoustic reflex measurement in order to meet the need for better temporal resolution and more accurate threshold delineation. We describe an approach to reflex measurement based on a signal averaging technique designed to examine both threshold and suprathreshold characteristics of the acoustic reflex. Results indicate that: (1) many supposed reflex threshold and latency aberrations are actually amplitude aberrations that are inappropriately classified because of instrumentation constraints; (2) reflex amplitude and waveform morphology can be recorded with appropriate fidelity using a signal averaging technique; (3) problems due to absolute amplitude variability can be minimized by using an index technique to assess amplitude relationships; (4) amplitude indices are sensitive indicators of neural pathology; (5) signal averaging and suprathreshold measurement of reflex amplitude and waveform morphology promise to enhance the sensitivity of acoustic reflex measurement.

Evaluation of the minimal auditory capabilities (MAC) test in prelingual and postlingual hearing-impaired adults.

The Minimal Auditory Capabilities (MAC) battery was used to evaluate the auditory performance of nine postlingual and ten prelingual adults with severe to profound hearing loss. Results suggest that degree of hearing loss overrides relative language skills as the primary factor affecting performance. The MAC battery appears promising as a tool for evaluating and monitoring both prelingual and postlingual adults using conventional hearing aids or cochlear implants.

Effect of ketamine on the stapedius reflex in the squirrel monkey.

We evaluated the effect of ketamine hydrochloride on the acoustically elicited stapedius reflex of squirrel monkeys. After intramuscular injection, in the presence of normal tympanometry, the amplitude of the contralateral stapedius reflex was severely depressed, even at low, preanesthetic dose levels. Possible mechanisms for the mediation of this unexpected effect are discussed.

The human acoustic tensor tympani reflex. A case report.

In a patient with unilateral lower motoneuron facial paralysis secondary to Bell's palsy, we evaluated the characteristics of what we believe to be an acoustically-evoked reflex contraction of the tensor tympani muscle. Ipsilateral stimulation of the involved ear yielded a pattern of impedance change different from the pattern characterizing normal stapedius muscle contraction. Threshold of the reflex was elevated, amplitude was large and variable, onset latency was greater, onset rise was more gradual, and offset decay was more rapid. Contralateral stimulation, with probe in the involved ear, failed to elicit the reflex contraction. Upon return of facial nerve function, the normal stapedius reflex contraction reappeared in response to both ipsilateral and contralateral stimulation.