Diagnosis, prevention and treatment of hereditary sensorineural hearing loss

Functional magnetic resonance imaging: contemporary and future use

PURPOSE OF REVIEW

Functional magnetic resonance imaging is a relatively new neuroimaging technique that is being used in both research and clinical applications. Increasing work has been done to elucidate the auditory cortex.

RECENT FINDINGS

Current studies focus on enhancing the sensitivity of functional magnetic resonance imaging in studying the auditory cortex and subcortical pathways in response to tonal stimulation, to evaluate the integrity of the auditory cortex before cochlear implantation, and as a screening tool for hearing impairment in the young child.

SUMMARY

Recent work has been encouraging: silent functional magnetic resonance imaging techniques allow for better evaluation of the auditory cortex with less confounding scanner noises. Functional magnetic resonance imaging can be safely and reproducibly performed in hearing-impaired children and in the preoperative evaluation of candidates for cochlear implantation.

A prospective case-controlled study of patients presenting with idiopathic sensorineural hearing loss to examine the relationship between hyperlipidaemia and sensorineural hearing loss

The prevalence of hyperlipidaemia in the normal population means that hyperlipidaemia is often found in patients who have a hearing loss of unknown aetiology. We prospectively undertook a case-controlled study of 85 patients presenting consecutively with a sensorineural hearing loss of unknown aetiology to see if the prevalence of hyperlipidaemia differed between the group with an idiopathic sensorineural hearing loss and a control population. Control subjects were recruited from patients undergoing nasal surgery for structural abnormalities. Both the study and control groups were also compared with the National Study of Hearing data. Hyperlipidaemia was no more prevalent in a population with idiopathic sensorineural hearing loss than a control population. No consistent association between hyperlipidaemia and hearing loss was found.

Hearing loss in Townes-Brocks syndrome

Townes-Brocks syndrome is an autosomal dominant syndrome consisting of anomalies affecting the ear, hand, foot, anus, and kidney. Anomalies affecting the ear include lop ear, preauricular skin tags, ossicular abnormalities, and a mixed hearing loss. The hearing loss in Townes-Brocks syndrome is predominantly sensorineural, affects high-frequency thresholds more than low-frequency thresholds, and has a variable (usually small) conductive component. The sensorineural component of the hearing loss is slowly progressive. It is typically in the mild range (20 to 40 dB hearing level) during early childhood and progresses to the moderate hearing loss range (40 to 60 dB hearing level) by early adulthood. We present a description of the otologic manifestations and an analysis of audiologic findings in six members of a family with Townes-Brocks syndrome.

Dizziness in childhood

There is a scant literature regarding vestibular evaluation of children with complaints of dizziness or vertigo. Considerable time and effort are expended on the problem and prevention of hearing loss in children, yet we often ignore concurrent or subsequent vestibular disorders. This neglect could be due to several factors, perhaps the most common being the fact that vertiginous crises in childhood are often attributed to problems of behavior or incoordination. In this article, we offer an approach to the dizzy child based on presenting symptoms. We discuss features of the history, examination, and laboratory evaluation key to determining the cause of dizziness. Finally, we discuss management, which varies according to the diagnosis.

Progressive hearing loss in Usher's syndrome

In 18 patients with Usher's syndrome, progressive hearing loss was verified audiologically in eight cases. Despite poor auditory threshold values and low speech discrimination scores, there was only one patient who could not communicate with speech. The possibility of hearing impairment being mainly progressive in Usher's syndrome is discussed.

Further evidence of a relation between noise-induced permanent threshold shift and vibration-induced digital vasospasms

The relation between noise-induced permanent threshold shift (NIPTS) and vibration-induced dysfunction in the digital circulation was examined in a longitudinal survey among forest workers. The survey was based on annual examinations done between 1972 and 1983. Thirty-two forest workers with digital vasospasms were compared with referents matched for age, exposure, and use of ear protectors. No significant differences between the groups were observed at 1,000 or 2,000 Hz. The forest workers with digital vasospasms had significantly greater NIPTS at 4,000 and 8,000 Hz than the symptom-free referents. During the follow-up period, the gap in NIPTS between the two groups did not increase. Vibration measurements from chain saws manufactured in different years indicated that chain saws manufactured after 1970 had a tenfold reduction in vibration, whereas the reduction in noise levels was only slight. The results suggest that vibration-induced activation of the autonomic nervous system, which is thought to elicit digital vasospasms, may also contribute to the development of NIPTS.

An unusual otological manifestation of Usher's syndrome in four siblings

A family in which four out of ten siblings affected by Usher's syndrome, with progressive hearing loss, is described. Two of the siblings had hearing loss while of school age, but two others first exhibited otological symptoms in their thirties. One of the siblings had retinitis pigmentosa, diagnosed before the hearing impairment became evident. The family seems to exhibit type III Usher's syndrome with unusual manifestations.

Metabolic management in Menière's disease

Pollution in the bloodstream by abnormal amounts of metabolites (sugar, insulin, triglycerides and cholesterol) over an extended period of time will have an adverse effect upon the small blood vessels: the arterioles, capillaries and venules. If the microcirculation of the inner ear becomes afflicted, it may produce endolymphatic hydrops. Control of blood pollution can usually be achieved by intelligent dietary management; and, in the case of Menière's disease, the clinical relief is gratifying. Carbohydrate and lipid metabolism is complicated. If the new insulin-glucose tolerance test is used, it will detect many more cases of glucose intolerance. Fifty consecutive cases of Menière's disease were studied for abnormal levels of metabolites. Thirty-eight (76 %) of these cases had either an abnormal glucose tolerance test (using the Wilkerson point system) or at least borderline insulin levels: a) abnormal insulin levels, 35 cases; b) borderline insulin values, 3 cases; c) abnormal glucose tolerance with normal insulin values, no cases; d) both normal glucose tolerance and normal insulin production, 12 cases.

Neurochemistry of the auditory system

Two areas of auditory biochemistry are reviewed: the identification and characterization of neurotransmitters in the auditory system and the biochemical approach to the study of genetic hearing disorders. Studies to identify neurotransmitters at major auditory synapses are outlined. Evidence supporting glutamate or aspartate as the neurotransmitter for the auditory nerve is presented. The application of biochemistry to the study of genetic hearing disorders is discussed.

Progressive sensorineural hearing loss and cochlear otosclerosis: a prospective study

The association of otosclerosis with reduced bone conduction is well known but no experimental or valid clinical relationship has been established to confirm this relationship. The purpose of this presentation is to demonstrate a clinical relationship between otosclerosis and sensorineural hearing loss. Experimental proof will await the accumulation and study of temporal bones of those individuals who, in life, exhibited the clinical relationship to be developed in this dissertation.

Auditory nerve and brain stem volume-conducted potentials evoked by pure-tone pips in the CBA/J laboratory mouse

The short latency (less then 10 ms) auditory nerve and brain stem evoked potentials of Jewett were examined in the inbred CBA/J laboratory mouse. Tone pips, at nine frequencies from 4 to 64 kHz, were used to determine auditory nerve evoked potential (P1) thresholds. Maximum sensitivity occurred at 32 kHz, and a second sensitive area was seen at 56 kHz. With the exception of 32 kHz, as stimulus frequencies were increased in octave intervals, the 90 dB P1 amplitude also increased. P1 latency decreased as the stimulus frequency was increased up to 32 kHz, but this trend reversed with further increases of frequency. However, the P1 amplitude-latency function produced a better agreement of latency and frequency with the travelling wave theory for amplitudes less than 1 micro V, while amplitudes from 2 to 8 micro V were independent of frequency. Latency and amplitude input-output functions for responses from the four auditory brain stem loci suggest that auditory information is differentially processed as a function of frequency at each level, This is especially true for the inferior colliculus, which is most sensitive to 8-KHz stimuli.