Effects of acoustic stimuli used for vestibular evoked myogenic potential studies on the cochlear function.

OBJECTIVE: To study if acoustic stimuli used for vestibular evoked myogenic potential (VEMP) studies can damage the cochlea. STUDY DESIGN: Prospective diagnostic study. SETTING: Academic tertiary referral center. METHODS: In 30 young healthy adults aged between 20 and 35 years without any audiovestibular disorders, cVEMP studies were performed in a standard setting (tone burst, 500 Hz, 133 dB SPL, stimuli rate 200). Before and after acoustic stimulation for the cVEMP examination, the cochlear function was measured using pure tone audiometry and distortion product otoacoustic emissions (DPOAE). Additionally, the subjects were asked about ear symptoms. RESULTS: In all subjects, cVEMP could be recorded. Eight (27%) of them reported subjective hearing symptoms direct after the VEMP examination. All were again free of complaints on the next day. Hearing thresholds did not deteriorate in pure tone audiometry. DPOAE levels decreased on the exposed side in the high-frequency range (4,000-6,000 Hz). The subjects with subjective ear symptoms had a stronger level decrease. In a follow-up measurement 24 hours later, the DPOAE levels showed recovery. CONCLUSION: Acoustic stimuli used to elicit VEMP were found to have an adverse effect on the cochlear function. A clinically relevant hearing loss was not found in our study in healthy adults. Subjective auditory symptoms were reversible within 24 hours. Nevertheless, the stimulus levels and the number of repetitions should be kept as low as possible.

Simvastatin and Ginkgo biloba in the treatment of subacute tinnitus: a retrospective study of 94 patients.

OBJECTIVES: Studies suggest that hypercholesterolemia promotes the development of inner ear disorders such as tinnitus. However, the underlying pathomechanisms are still not clearly defined. METHODS: A retrospective study was performed to assess whether a reduction of serum cholesterol by 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors may result in a relief of subacute tinnitus. Remission rates of 58 patients were investigated after 4 months of treatment with simvastatin (40 mg). Results were compared to treatment with Ginkgo biloba (120 mg; n = 36) as control group. Differences between tinnitus score at the day of first treatment and after 4 months were used as main outcome measure. RESULTS: After treatment with simvastatin or G biloba, tinnitus score decreased from 41.3 ± 10.4 to 37.4 ± 17.3 and from 44.7 ± 11.2 to 41.2 ± 8.7, respectively. However, independently of the treatment regimen, differences of tinnitus scores were considered not significant. CONCLUSIONS: After administration of simvastatin over 4 months, this retrospective study has shown no significant efficacy in treatment of subacute tinnitus. For a more conclusive answer, further prospective, double-blind, and placebo-controlled studies with a larger number of patients are needed.

Quantitative estimation of minor conductive hearing loss with distortion product otoacoustic emissions in the guinea pig.

Subclinical conductive hearing losses (CHLs) can affect otoacoustic emissions and therefore limit their potential in the assessment of the cochlear function. Theoretical considerations to estimate a minor CHL from DPOAE measurements [Kummer et al. (2006). HNO 54, 457-467] are evaluated experimentally. They are based on the fact, that the level difference of the stimulus tones L(1) and L(2) for optimal excitation of the inner ear is given by L(1)=aL(2)+b. A CHL is presumed to attenuate both L(1) and L(2) to the same extent such that excitation of the inner ear is no longer optimal. From the change of L(1) that is necessary to restore optimal excitation of the inner ear and thus to produce maximal DPOAE levels, the CHL can be estimated. In 10 guinea pig ears an experimental CHL was produced, quantified by determination of compound action potential (CAP) thresholds at 8 kHz (CHL(CAP)) and estimated from DPOAE measurements at 8 kHz (CHL(DPOAE)). CHLs up to 12 dB could be assessed. CHL(DPOAE) correlated well with CHL(CAP) (R=0.741, p=0.0142). Mean difference between CHL(DPOAE) and CHL(CAP) was 4.2±2.6 dB. Estimation of minor CHL from DPOAE measurements might help to increase the diagnostic value of DPOAEs.

Photoirradiation therapy of experimental malignant glioma with 5-aminolevulinic acid.

OBJECT: Accumulation of protoporphyrin IX (PPIX) in malignant gliomas is induced by 5-aminolevulinic acid (5-ALA). Because PPIX is a potent photosensitizer, the authors sought to discover whether its accumulation might be exploited for use in photoirradiation therapy of experimental brain tumors, without injuring normal or edematous brain. METHODS: Thirty rats underwent craniotomy and were randomized to the following groups: 1) photoirradiation of cortex (200 J/cm2, 635-nm argon-dye laser); 2) photoirradiation of cortex (200 J/cm2) 6 hours after intravenous administration of 5-ALA (100 mg/kg body weight); 3) cortical cold injury for edema induction; 4) cortical cold injury with simultaneous administration of 5-ALA (100 mg/kg body weight) and photoirradiation of cortex (200 J/cm2) 6 hours later; or 5) irradiation of cortex (200 J/cm2) 6 hours after intravenous administration of Photofrin II (5 mg/kg body weight). Tumors were induced by cortical inoculation of C6 cells and 9 days later, magnetic resonance (MR) images were obtained. On Day 10, animals were given 5-ALA (100 mg/kg body weight) and their brains were irradiated (100 J/cm2) 3 or 6 hours later. Seventy-two hours after irradiation, the brains were removed for histological examination. Irradiation of brains after administration of 5-ALA resulted in superficial cortical damage, the effects of which were not different from those of the irradiation alone. Induction of cold injury in combination with 5-ALA and irradiation slightly increased the depth of damage. In the group that received irradiation after intravenous administration of Photofrin II the depth of damage inflicted was significantly greater. The extent of damage in response to 5-ALA and irradiation in brains harboring C6 tumors corresponded to the extent of tumor determined from pretreatment MR images. CONCLUSIONS: Photoirradiation therapy in combination with 5-ALA appears to damage experimental brain tumors selectively, with negligible damage to normal or perifocal edematous tissue.