Louis W. Welsh

Functional impairments due to unilateral deafness.

The authors investigated the impact of unilateral listening upon two central auditory functions: speech discrimination in a noisy environment, and the ability to process and clearly recognize modestly accelerated speech by 30% compression (shortened exposure). We determined that the negative impact of listening to speech in the milieu of noise was individually variable. The data revealed a wide range of impairment, from mild to relatively severe (ie, 0% to 60% [mean, 34%]; normative data, 4% to 36% [mean, 14%]). The performance scores for recognition of compressed sentences were not markedly influenced by unilateral deafness, but the functional results of the residual ear were correlated with a loss of high-frequency sensitivity (mean of 54% correct in severe unilateral deafness with an associated high-frequency loss versus 93% correct in normal controls). Reorganization of the central nervous system by “plasticity” or biological maturation over time failed to improve the performance of monaural listening. The currently recommended methods of remediation for this sensory deficit are discussed, and newer technologies under investigation are examined.

Vertigo: Analysis by Magnetic Resonance Imaging and Angiography

The relationship of vascular disease of the vertebrobasilar artery system to isolated vertigo was examined by magnetic resonance imaging and angiography. Eighty-nine individuals complaining of vertigo were evaluated by standard otoneurologic investigations, and the data were correlated with the vascular patterns of the cervical region and posterior fossa. The age distribution extended from the fourth decade to the ninth decade; the peak occurrence was observed in the eighth. Approximately 85% of the group experienced numerous episodes of vestibular dysfunction from months to years before examination; the remaining segment was examined following the first episode due to severity or persistence of symptoms. The criteria for vascular abnormality proposed by the authors are based upon comparison with previous normal findings. Approximately 52% of the cohort demonstrated abnormal configurations or evidence of diminished flow within the vertebrobasilar artery system. Of this segment, a vertebral artery was most frequently abnormal, in 76%; the basilar artery was judged pathological in 32%, and combined disease of several arteries was evident in 20%.

Basilar artery and vertigo.

Our goal was to identify by magnetic resonance angiography the specific vascular abnormalities of the basilar artery that can be related to hypoperfusion disorders and produce symptoms of vertebrobasilar insufficiency. A classification of regional vascular perfusion disorders based on developmental malformations and intrinsic and extrinsic angiopathies was formulated from an analysis of individuals with these disorders. Specific angiographic abnormalities such as tortuosity, stenosis, thrombosis, and dolichoectasia were identified in subjects with vestibulocerebellar dysfunction. Charts and radiographic images were examined with respect to the history, physical evidence, and vascular configuration, and the data were integrated for comprehensive analysis. We found that abnormalities identified by magnetic resonance angiography could be correlated with symptoms due to vascular insufficiency. Cases are presented that document the developmental and acquired arterial disorders that may be considered the etiologic factors for regional perfusion deficits.

Current Evaluation of Pseudohypacusis: Strategies and Classification

Some cases of pseudohypacusis may involve medicolegal aspects and require a confirmed and quantitative diagnosis. These challenging cases must be identified, and then evaluated with basic audiologic and sophisticated electrophysiologic tests. Data on 64 patients with pseudohypacusis collected over a 4-year period are reported. A classification system was developed from an analysis of these cases and is presented for clinical evaluation and diagnosis. In many cases, conventional audiologic evaluation involving pure tone and speech audiometry may be adequate and sufficient for diagnosis. In more complex cases, evoked otoacoustic emissions (EOAEs) and auditory brain stem responses (ABRs) are needed for confirmation of peripheral auditory sensitivity. We found that EOAEs were the most rapid, economical, and objective method, and confirmed the diagnosis of hearing loss in 78.1 % of cases. Fifteen percent of subjects required ABRs to substantiate the diagnosis. The reliability of basic audiologic tests based on previous clinical investigations and data from the literature are discussed. We conclude that a thorough knowledge and understanding of pseudohypacusis is essential to verify the existence of pseudohypacusis, to determine its type, and to quantify the auditory thresholds.

Alström syndrome: progressive deafness and blindness.

Alström syndrome is a very rare, genetically transmitted disorder that affects special sense functions, resulting in progressive visual and auditory impairment. The diagnostic criteria for this disorder are presented, and the differential issues between it and other, similar syndromal forms of sensory and multisystem dysfunction are discussed. A report of 2 siblings so involved is summarized. The disability of other organs is considered, namely, the kidney, the heart, and the metabolic and endocrine systems.

Evaluation of Vertigo by Auditory Brain Stem Response

The authors examined the hypothesis that abnormal patterns of the auditory brain stem response (ABR) could supplement the neuro-otological evaluation and assist in localizing the site of vestibulocerebellar dysfunction. This project is based upon the fact that the sources of waves I through V have been regionally identified. Absent or delayed patterns can be referenced to the normal data, and the site of a lesion generating vertigo can be established. We found absence of waves or prolonged interpeak latencies in 25% of the vertiginous subjects with normal hearing and magnetic resonance images of the brain. We conclude that in selected cases, lesions affecting the vestibular system can influence the ABR, and the electrophysiological tests of audition may suggest regionalization of the dysfunction in the hindbrain and midbrain.

Incompetent circle of Willis and vertebrobasilar insufficiency.

An analysis of the vascular basis of vertebrobasilar insufficiency was derived from the examination of 135 subjects by magnetic resonance imaging and angiography. The data from this cohort were compared to those from normal, ie, asymptomatic, individuals. We concluded that there is a significant difference in the potential for intracerebral collateralization and regional perfusion due to structural defects such as stenosis or developmental absence of the posterior communicating arteries in this symptomatic group. In addition, an occlusion of one or more of the source vessels, the internal carotid and vertebral arteries, in conjunction with an incomplete circle of Willis increased the potential for hindbrain perfusion deficits. Clinical cases illustrate the relationship between failure of internal shunting and the myriad symptoms of hindbrain dysfunction.

Clinical interpretations of transient otoacoustic emissions

PURPOSEnThe purpose of this study was to characterize the relation of different ordinal patterns of transient otoacoustic emissions (TEOAES) with respect to underlying otologic disorders and auditory status.nnnPATIENTS AND METHODSnThe results of TEOAEs in 225 patients with various auditory disorders were investigated and compared with normative data established from 90 subjects of various ages. TEOAEs were categorized according to four patterns: (1) normal (general response level within 90% of normative data, (2) reduced amplitude (general response level was > or =2 dB peak sound pressure level (pSPL), but less than the mean -1.64 SD of the normative data), (3) abnormal morphology of frequency spectrum (general response level was within normal limits, but reduced at > or =2 individual octave frequencies between 1,000 and 5,000 Hz), and (4) total absence (response level <2 dB pSPL).nnnRESULTSnThis study showed that the normal pattern of TEOAEs, in terms of response amplitude, varied with age. Our results further indicated that a reduced amplitude pattern of TEOAEs was noted in patients with a mild sensorineural hearing loss (SNHL), negative tympanometric pressure, a pressure-equalization tube, and Menieres disease. TEOAEs provided good frequency-specific information for patients with a noise-induced hearing loss. All patients with ossicular chain abnormalities, more than moderate SNHL, and a middle ear mass or effusion had total absence of TEOAEs. Patients with acoustic neuroma and brainstem lesions presented a complex profile of TEOAEs. In the follow-up of auditory function in patients undergoing otologic surgery, different patterns of TEOAEs between the preoperative and postoperative recordings were evident, which correlated with the hearing thresholds and middle ear status. The abnormal findings of TEOAEs due to specific auditory diseases were discussed.nnnCONCLUSIONnThe interpretation of TEOAEs can be facilitated through an analysis of specific patterns and in combination with other audiologic tests.

Vascular analysis of individuals with drop attacks.

The authors used magnetic resonance angiography to examine the intracranial and cervical vascular structures of individuals who suffer from drop attacks. Normal structural configurations of the circle of Willis and the vertebrobasilar arterial system were compared to the vascular patterns of 10 subjects with these episodic tonic or atonic attacks. Overall, multiple areas of arterial occlusion, stenosis, or hypoplasia were visualized in the images of 8 of the 10 subjects. Specific anomalies of the vertebral and basilar arteries were identified in 4 individuals, and 8 images depicted nonvisualization of the posterior communicating arteries. We suggest that the pathological aberrations in the regional circulation of the hindbrain support the hypothesis that a transient hypovolemic episode may have an impact upon the neural activity involved in maintenance of motor tone and postural stability.

Function of a hearing aid under stressful conditions

The auditory function of individuals with normal hearing was compared with that of hearing-aided subjects of similar age to determine whether amplification remediates hearing impairment under stressful auditory situations. The specific tests of listening in a competitive noise environment and identifying moderately compressed speech were introduced to adequately aided individuals. The data indicate that noise had an impact on auditory function to a much greater degree in aided individuals than in matched counterparts with normal hearing. The data derived from acceleration of simple sentences delivered to the aided group suggested that contrary to basic tonal sensitivity, the capacity to understand the stimulus was greatly compromised. The authors discuss cochlear damage and central auditory impairment as they relate to the limitations of amplification for sensorineural hearing loss.