Neurophysiological model of tinnitus: dependence of the minimal masking level on treatment outcome.

Validity of the neurophysiological model of tinnitus (Jastreboff, 1990), outlined in this paper, was tested on data from multicenter trial of tinnitus masking (Hazell et al., 1985). Minimal masking level, intensity match of tinnitus, and the threshold of hearing have been evaluated on a total of 382 patients before and after 6 months of treatment with maskers, hearing aids, or combination devices. The data has been divided into categories depending on treatment outcome and type of approach used. Results of analysis revealed that: i) the psychoacoustical description of tinnitus does not possess a predictive value for the outcome of the treatment; ii) minimal masking level changed significantly depending on the treatment outcome, decreasing on average by 5.3 dB in patients reporting improvement, and increasing by 4.9 dB in those whose tinnitus remained the same or worsened; iii) 73.9% of patients reporting improvement had their minimal masking level decreased as compared with 50.5% for patients not showing improvement, which is at the level of random change; iv) the type of device used has no significant impact on the treatment outcome and minimal masking level change; v) intensity match and threshold of hearing did not exhibit any significant changes which can be related to treatment outcome. These results are fully consistent with the neurophysiological interpretation of mechanisms involved in the phenomenon of tinnitus and its alleviation.

Contralateral suppression of transient evoked otoacoustic emissions: intra-individual variability in tinnitus and normal subjects.

Contralateral acoustic stimulation reduces the amplitude of the transient evoked otoacoustic emission (TEOAE) in humans. The mechanism is thought to be mediated, at least in part, through the medial olivocochlear efferent system innervating the outer hair cells. To assess its usefulness as a possible clinical test, TEOAE suppression was measured in each ear of 12 subjects over a 6-week period, and these data are shown in detail for four subjects representing extremes of variability in a tinnitus and a non-tinnitus group. Intra-subject test results (n = 18) exhibited a varying extent of suppression values and the variance of each session, consisting of three tests, was not statistically different from one session to another. There was no dependence on variables such as ear (right or left), session, day of testing or their interaction. There was a significant difference in the variability between the tinnitus and the normal group.

A neurophysiological approach to tinnitus: clinical implications.

This paper presents a neurophysiological approach to tinnitus and discusses its clinical implications. A hypothesis of discordant damage of inner and outer hair cells systems in tinnitus generation is outlined. A recent animal model has facilitated the investigation of the mechanisms of tinnitus and has been further refined to allow for the measurement of tinnitus pitch and loudness. The analysis of the processes involved in tinnitus detection postulates the involvement of an abnormal increase of gain within the auditory system. Moreover, it provides a basis for treating patients with hyperacusis, which we are considering to be a pre-tinnitus state. Analysis of the process of tinnitus perception allows for the possibility of facilitating the process of tinnitus habituation for the purpose of its alleviation. The combining of theoretical analysis with clinical findings has resulted in the creation of a multidisciplinary Tinnitus Centre. The foundation of the Centre focuses on two goals: the clinical goal is to remove tinnitus perception from the patient's consciousness, while directing research toward finding a mechanism-based method for the suppression of tinnitus generators and processes responsible for enhancement of tinnitus-related neuronal activity.

Electrical tinnitus suppression: frequency dependence of effects.

Electrical stimulation through a round window electrode has been evaluated in 9 patients with unilateral deafness and severe tinnitus. Three subjects were permanently implanted with positive long lasting results. Analysis of the threshold of sound perception, tinnitus suppression and auditory discomfort levels as a function of current frequency revealed the advantage of low frequency stimulation. In 2 patients the loudness of electrically evoked sound perception was balanced against tones in the hearing ear. Our results can be interpreted as indicating that processes other than auditory masking are responsible for electrical tinnitus suppression.

Positional audiometry in the diagnosis of perilymphatic fistula.

Fifty-eight cases with a presumptive clinical diagnosis of perilymphatic fistula (PLF) are described with the results of a positional audiometric test designed to detect the presence of air in the cochlea. All patients underwent tympanotomy and observations of the middle ear are recorded together with the results of treatment. A definite leak was found in 33 cases and none in 25, but grafting of the round and oval window was performed in all but 10 cases. Pure-tone audiometry was performed before and after a 30-minute period of positioning the patient horizontally with the affected ear uppermost. A change in audiometric thresholds was noted in the group where a presumptive diagnosis of PLF was made, including some of those not found to have leaks at operation. However these changes were not observed in the positional tests of a group of 22 patients with hearing losses attributable to other causes. Also, an abnormal air-bone gap was noted in the PLF group compared with the other group. Although the original two-frequency criteria of earlier studies applied to the positional test did not predict the operative findings (leak or no leak), new data on frequency specific changes are presented. It is possible that fistulas at the oval window may be associated with positional threshold change at 500 Hz, and those at the round window with changes at 8 kHz.

Tinnitus. III: The practical management of sensorineural tinnitus.

A weekly tinnitus clinic at University College Hospital, London, has been in existence since 1976. By developing a holistic and multidisciplinary approach to the management of tinnitus, we have been able to help the majority of patients referred with severe and disabling tinnitus. We have developed a protocol for the clinical assessment of tinnitus as a disability, and a strategy of investigation and reassurance based on the patient's understanding of the underlying mechanisms involved in tinnitus generation. Most treatment is aimed at bringing about a process of habituation (which occurs naturally in the majority of people experiencing tinnitus over a period of time). Symptom control is required in about half the patients referred, and various techniques are discussed including prosthetic masking devices, psychological approaches, drug therapy and electrical tinnitus suppression.

Tinnitus. I: Auditory mechanisms: a model for tinnitus and hearing impairment.

A model is proposed for tinnitus and sensorineural hearing loss involving cochlear pathology. As tinnitus is defined as a cortical perception of sound in the absence of an appropriate external stimulus it must result from a generator in the auditory system which undergoes extensive auditory processing before it is perceived. The concept of spatial nonlinearity in the cochlea is presented as a cause of tinnitus generation controlled by the efferents. Various clinical presentations of tinnitus and the way in which they respond to changes in the environment are discussed with respect to this control mechanism. The concept of auditory retraining as part of the habituation process, and interaction with the prefrontal cortex and limbic system is presented as a central model which emphasizes the importance of the emotional significance and meaning of tinnitus.

Tinnitus. II: Surgical management of conditions associated with tinnitus and somatosounds.

The literature relating to the effects of otological surgery on tinnitus is reviewed. The results of such surgery are often unpredictable with respect to postoperative tinnitus, and ablative surgery may well make the tinnitus worse. The concept of somatosounds (tinnitus arising from outside the auditory pathway) is presented, and the management of some conditions, including patulous Eustachian tube and palatal myoclonus, is discussed.

Desferrioxamine ototoxicity: evaluation of risk factors in thalassaemic patients and guidelines for safe dosage.

Forty-seven patients with thalassaemia have been studied to define risk factors for development of sensorineural hearing loss, and to establish guidelines for safe chelation. Sensorineural hearing loss was only present in patients who had previously received desferrioxamine (DFO). The two most significant risk factors were the maximum dose of DFO previously received (P less than 0.01), and a serum ferritin of less than 2000 micrograms/l at that time (P less than 0.001). A therapeutic index obtained from the ratio of the mean daily dose of DFO mg/kg divided by the serum ferritin identifies patients with a ratio of greater than 0.025 as at risk of sensorineural hearing loss (P less than 0.001) and can be used as a guideline for safe DFO dosage. Follow-up audiometry of the affected patients over a 2-year period indicated that adjustment of the dose to a therapeutic index of less than 0.025 resulted in the stabilization of hearing loss in seven patients and improvement in two.

Non-invasive electrical stimulation of the ear canal as a communication aid in acquired total deafness.

Some profoundly deafened patients, who cannot be helped by sound amplification, claim to perceive auditory sensations when alternating currents up to 100 Hz are passed through electrodes applied to the skin of the external ear canal. A portable speech processor has been developed which supplies this current. The signal is a balanced square wave, the frequency of which is proportional to the first formant frequency. The amplitude is proportional to the intensity of voiced sounds. In order to fit the narrow frequency and dynamic range of the electrical stimulus, the speech processor produces a downward frequency transposition and strong limitation of the dynamic range. The device has been tested for (1) discrimination of environmental sounds; (2) question/statement discrimination; (3) identification of vowels and consonants in vowel/consonant/vowel context; (4) lip-reading with and without the prosthesis.

Patulous eustachian tube syndrome: the relationship with sensorineural hearing loss. Treatment by eustachian tube diathermy.

The patulous Eustachian tube syndrome has previously been regarded as a troublesome but benign condition. Nine out of 13 patients reported here had evidence of cochlear damage similar to that caused by acoustic trauma. These patients also had vestibular symptoms which improved with treatment of the patulous tube. It is postulated that abnormal patency of the Eustachian tube may allow excessive middle ear pressure changes to occur which may be transmitted by abnormal ossicular movement to the cochlea. Eustachian tube diathermy using a ureteric diathermy probe is a safe and effective method of treating this condition.

Electrical tinnitus suppression (ETS) with a single channel cochlear implant.

Patients with intractable tinnitus in a dead ear were selected for electrical tinnitus suppression (ETS) first with a round window electrode inserted via the ear canal. Three patients have been selected for implantation with a UCH/RNID single channel extracochlear device to use with a sinusoidal tinnitus suppressor. We have also examined the effect of sinusoids on deafened implantees with tinnitus and conclude that tinnitus can be suppressed in some individuals with low frequency sine waves. Two patients are presented who have used cochlear implants to suppress their tinnitus for more than 18 months.

The suppression of palatal (or intra-tympanic) myoclonus by tinnitus masking devices. A preliminary report.

Twelve cases of well established palatal myoclonus with objective clicking tinnitus were treated with tinnitus masking techniques. After a few months, three patients became completely symptom free, one for five years now. A further four patients continued to get periods of relief from their clicking sounds with continuous masking, and four patients found the distracting effects of the white noise helped them. The mechanism of palatal myoclonus is discussed with reference to the part played by masking therapy in this condition.

The UCH/RNID cochlear implant programme: patient selection.

After an initial postal questionnaire, patients undergo a series of tests and assessments designed to establish their suitability for implantation. The following criteria should be met: Total or profound post-lingual hearing loss. Sufficient age to give informed consent. General good health. Psychological stability. Unable to benefit from hearing aids. Free from middle ear or mastoid disease. Detailed medical, audiometric, vestibular and psychological investigations are performed, as well as acute electrical stimulation of the cochlea, and a hearing aid trial in those subjects with some measurable hearing. Fifty-two applicants have so far been assessed and of these 14 have been found to be suitable for implantation and seven have received implants.

A clinical study of tinnitus maskers.

This report describes a three-centre study of the effectiveness of tinnitus maskers, combination instruments (masker plus hearing aid), and hearing aids in the management of tinnitus. Some 472 patients entered the study with 382 reaching the first evaluation session after a minimum period of 6 months from fitting, and 206 reaching the second evaluation not less than 6 months after the first. The study included two control groups, by which to assess the comparative benefit to be derived solely from the investigation and counselling of such patients. The principal results were as follows: thorough investigation and careful counselling do much to help the patient; much further benefit is given by tinnitus masking instruments of various kinds; maskers are more often effective than hearing aids, although the latter are frequently the most appropriate first treatment of those patients who have substantial (but not yet treated or insufficiently treated) hearing difficulties as well; there is no evidence of masking having any harmful effect on hearing. None of the audiometric or tinnitus tests currently employed can be regarded as predictive, either of tinnitus severity, or of the eventual outcome of masking therapy, however certain measurements may help as a guide to patient management.

Identification of sensory neural hearing loss in very preterm infants by brainstem auditory evoked potentials.

Brainstem auditory evoked potentials were recorded in 117 newborn infants of less than 33 weeks of gestation. The potentials were absent in 10 infants (bilaterally in eight and unilaterally in two) and present in 107. By 1 year of age nine of the 10 infants with absent brainstem auditory evoked potentials were shown to have sensory neural hearing loss and required hearing aids: the remaining infant had secretory otitis media. None of the 107 infants whose auditory evoked potentials were present were found to have sensory neural hearing loss but 13 had secretory otitis media. Measurement of brainstem auditory evoked potentials is an accurate method of identifying sensory neural hearing loss in very preterm infants.