Hearing loss after noise exposure

The higher field strength magnetic resonance imaging (MRI) such as 3 Tesla (T) and above generates noise that has potential detrimental effects on the hearing. Temporary threshold shifts following MRI examination have been reported for MRI with lower field strength. Such effect, however, have not been reported so far for a 3 T MRI. We report a case that exemplifies the possible detrimental effects of a 3 T MRI generated noise on the auditory system. Our patient underwent investigation of his chronic backache in a 3 T MRI unit and developed hearing loss and tinnitus post-MRI examination. Hearing assessment was done using pure tone audiogram, distortion product otoacoustic emission (DPOAE) and brainstem electrical response audiometry (BERA) which revealed a unilateral sensorineural hearing loss which recovered within 3 days. However the tinnitus persisted. This is possibly a case of temporary threshold shift following noise exposure. However a sudden sensorineural hearing loss remains the other possibility.     

Hearing loss in a pediatric patient following cisplatin chemotherapy and subsequent exposure to excessive noise

Cisplatin is a commonly-used chemotherapeutic agent that is highly-effective against a variety of pediatric cancers. Unfortunately, it may lead to ototoxicity, with serious consequences on the quality of life of survivors. Patients remain at risk of progression of ototoxicity even after completion of treatment. We report the case of a medulloblastoma survivor with previously documented normal hearing, who developed significant hearing loss and tinnitus following exposure to excessive noise at a nightclub three years after completion of treatment. We highlight the importance of long-term audiological follow up and education about the increased risk of hearing loss in this population.     

Hearing loss following exposure during development to polychlorinated biphenyls: a cochlear site of action

Maternal exposure to polyhalogenated hydrocarbons results in early postnatal hypothyroxenemia and a low-frequency hearing loss in adult offspring (Goldey et al., 1995a. Toxicol. Appl. Pharmacol. 135, 67-76; Herr et al., 1996. Fundam. Appl. Toxicol. 33, 120-128). The purpose of the present work was to determine whether the site-of-action of this auditory impairment was within the cochlea. Primiparous Long-Evans rats were given daily oral doses of corn oil (control) or 8 mg/kg of the commercial PCB mixture Aroclor 1254 (A1254) from gestation day (GD) 6 through postnatal day (PND) 21. Auditory thresholds for 1-, 4-, 16-, and 40-kHz tones were assessed using reflex modification audiometry in young adult offspring on postnatal days (PND) 92-110. Approximately 6 weeks after auditory assessments, a subset of animals (n=4 per group) were killed for histological assessment of the cochlea. Surface preparations of the organ of Corti were prepared from one cochlea per animal and modiolar sections were prepared from the opposite cochlea. Consistent with previous findings, auditory thresholds for 1-kHz tones were elevated by approximately 25 dB in the A1254-exposed animals. Thresholds for all higher frequencies were not different compared to controls. Surface preparations of the organ of Corti revealed a mild to moderate loss of outer hair cells in the upper-middle and apical turns. Inner hair cells were not affected. Modiolar sections failed to reveal alterations in any other cochlear structures. There was also no apparent loss of ganglion cells. These data clearly link the loss of low-frequency hearing caused by exposure during development to A1254 to a loss of outer hair cells in the organ of Corti. The mechanism that underlies this developmental ototoxicity remains to be determined. These data provide the first evidence of a structural deficit in the nervous system of adult animals exposed to PCBs during development.     

Hearing loss due to cranio-metaphysial dysplasia

Craniometaphysial dysplasia is a rare cause of conductive hearing loss. It is a genetic disorder of bone due to decreased osteoclastic activity in the endosteal and periosteal regions of craniofacial and long bones. The characteristic temporal bone abnormalities are attic fixation, abnormally shaped ossicles and obliterated foramina ovale. Computerised tomography is helpful in predicting operative findings; surgery should be reserved for those with a severe hearing loss.     

Hearing loss due to noise trauma

Three different types of noise-induced hearing loss have been reported in the literature. The two less common types are described here. Three cases of these two types from our clinic are reported. Since these 2 types of noise-induced hearing loss often involve low frequencies it is important to recognize them in compensation cases.     

Hearing loss and cochlear pathology in the monkey (Macaca) following exposure to high levels of noise

Summary Eight Old World monkeys were exposed 8 h daily for 20 days to octave-band noise having center frequencies from 0.5–8 kHz at levels of 117–120 dB SPL. Two additional animals received exposures to wide-band, 120-dB SPL noise on the same schedule, and one animal was exposed to the 2-kHz octave band for 40 h continuously. Behavioral audiograms were measured throughout exposure and during a 1-month recovery period. Following recovery, the animals were sacrificed and their ears examined histologically. Monaural audiograms are presented showing initial and final TTS and PTS measured at the end of the recovery period. These are compared with complete cytocochleograms for each ear. Hair cell loss was generally restricted to the outer rows, and was reasonably well correlated with pattern of hearing loss. Some cell loss, including inner hair cells, was found in the extreme basal turn, usually without associated high-frequency hearing loss. The relationships between exposure frequency, hearing loss, and locus of cochlear pathology are discussed, as are changes in TTS during exposure.This investigation was supported by research grants NS-05077, NS-05065 and NS-12706 and by Program Project grant NS-05785 from the National Institutes of Health     

Hearing acuity and susceptibility to noise-induced hearing loss

Above a critical level (CL) of fatiguing tone, temporary threshold shift (TTS) rises rapidly with intensity. Using a fatiguing tone of 1000 Hz, threshold shift following 1 min stimulation at varying intensities was measured at the same frequency in 55 normal subjects and the CL determined for each. In a second and more limited study, TTS was measured at a frequency half an octave above that of the fatiguing tone. A significant inverse correlation was established between hearing level (HL) and CL at the same frequency with a fall of 2.5 dB in the latter for every 10 dB rise in the former. CLs measured half an octave above the fatiguing tone frequency were appreciably lower by 5 to 11 dB. No correlation was apparent between TTS and HTL, implying that TTS and CL are subserved by differing physiological mechanisms. The findings have relevance to the topic of susceptibility to noise-induced hearing loss and the formulation of damage risk criteria.     

Hearing loss related to zinc deficiency in rats

Summary Based on the observation that the zinc concentration in the cochlea of guinea pigs is very high, Shambaugh in North America has suggested that zinc plays an important role in hearing. Zinc deficiency is not infrequently present in growing children and elderly people, and thus might result in a hearing loss, which should be treated with zinc supplementation. The present experiment examined the effects of a zinc-deficient diet on hearing in 7-week-old rats. The auditory brainstem response threshold was measured in four rats before, during and after a zinc-deficient diet. Concentrations of zinc in the brain and in several other organs were measured, and the cochleas were examined microscopically. No hearing loss or morphological change in the cochlea of these animals was detected, although a clear zinc-deficient status was reached.     

Hearing loss in carcinomatous meningitis

Although the syndrome of carcinomatous meningitis presenting as multiple cranial neuropathies is well known, hearing loss as a presenting complaint has not been previously stressed. Five cases of carcinomatous meningitis beginning as hearing loss are presented and the clinical and laboratory features discussed. A thorough review of the literature summarizes the pathology, pathogenesis and recommended modes of therapy of this disease and the importance of early diagnosis and treatment is stressed.     

听力减退与认知障碍

随着全球人口预期寿命的不断增长，人口老龄化已不再是工业化国家的专利。我国从2000年10月开始，60岁以上人口已超过10％，正式成为老龄化国家。与此同时，老龄化相关性疾病的发病率也一直在持续增加。如阿尔茨海默病（AD）的发病率从65岁时的1％上升到95岁时的75％。经测试后确定的老年性听力减退发生率差别极大（46％-83％），但总的趋势很高。总之，认知障碍和听力下降都是老年人121中发病率很高的两种疾病。因此听力减退与认知障碍之间的关系已经成为近年来相关领域的研究热点，但研究结论不尽统一，包括两者之间有无关系，是什么样的关系等等。在介绍该领域的研究进展之前，我们首先把听力界定为对听刺激的察觉和反应，而认知障碍是指认知功能直接或间接的下降。在此基础上，从流行病学研究中的横断面研究、纵向研究，以及干预性研究、实验室研究、区组比较和模拟实验等方面，分别介绍近年来的科研进展和实验成就，并就未来的发展方向进行预测。