RESUMEN
A leading cause of morbidity from bacterial meningitis is an irreversible, usually profound sensorineural hearing loss, with an incidence as high as 30% in some studies. Bacterial meningitis remains the most common cause of acquired postnatal sensorineural deafness. Although several clinical studies have examined the long-term outcome of hearing in meningitis, few studies have examined the time course of hearing loss during the acute course of the disease. We have developed an animal model of meningogenic hearing loss in the rat and have plotted the time course of that hearing loss. Serial auditory brain stem responses (ABRs) were measured in rats inoculated in the cisterna magna (subarachnoid space) with Streptococcus pneumoniae (10(5) to 10(7) colony-forming units). All rats injected developed meningitis as evidenced by increased cerebrospinal fluid (CSF) white cell counts and positive CSF cultures. Serial ABR measurements taken 6, 12, 15, 18, 21, and 24 hours after inoculation demonstrated significant threshold shifts and eventual loss of the ABR waveform as compared with measurements in control rats injected with sterile culture medium. Hearing loss began approximately 12 to 15 hours after inoculation and progressed to complete loss by 24 hours (17 of 18 animals). No correlation was found between the magnitude of hearing loss and CSF white cell count or bacterial titer. Temporal bone histology of rats with meningitis shows a dense inflammatory cell infiltrate throughout the subarachnoid space. Labyrinthine inflammatory cells were confined to the scala tympani. The cochlear aqueduct is the proposed route of infection from the meninges to the labyrinth (scala tympani). Endolymphatic hydrops was also noted throughout the cochlea. These experiments both establish a reproducible animal model of meningogenic hearing loss and support the hypothesis that this hearing loss is progressive rather than abrupt in onset and is related to the duration of untreated infection. CSF inflammatory cells appear to enter the cochlea through the cochlear aqueduct. This reliable animal model will enable future studies directed toward further understanding the pathogenesis and pathophysiology of this hearing loss.
Asunto(s)
Modelos Animales de Enfermedad , Pérdida Auditiva Sensorineural/microbiología , Meningitis Neumocócica/complicaciones , Enfermedad Aguda , Animales , Umbral Auditivo , Líquido Cefalorraquídeo/citología , Líquido Cefalorraquídeo/microbiología , Progresión de la Enfermedad , Potenciales Evocados Auditivos , Femenino , Pérdida Auditiva Sensorineural/diagnóstico , Pérdida Auditiva Sensorineural/patología , Recuento de Leucocitos , Meningitis Neumocócica/líquido cefalorraquídeo , Ratas , Ratas Wistar , Reproducibilidad de los Resultados , Hueso Temporal/patología , Factores de TiempoRESUMEN
Without access to adequate diagnostic facilities, management of vestibular and balance disorders can be a frustrating process for both clinicians and patients. Expert clinical staff and state-of-the-art tools for the evaluation of balance disorders and dizziness are available within the vestibular and balance center. These centers can provide referring physicians and their patients with access to diagnostic expertise and facilities not practical within a general practice environment. Providing detailed evaluative reports, balance centers can help the referring physician define directions for surgical and medical treatment and assist in the management and rehabilitative treatment of acute and chronic dizziness and balance dysfunction.
Asunto(s)
Mareo/etiología , Enfermedades del Sistema Nervioso/diagnóstico , Reflejo Vestibuloocular , Enfermedades Vestibulares/diagnóstico , Vestíbulo del Laberinto/fisiopatología , Diagnóstico Diferencial , Electronistagmografía , Movimientos Oculares , Femenino , Movimientos de la Cabeza , Humanos , Masculino , Sensibilidad y Especificidad , Pruebas de Función VestibularRESUMEN
The round window electromagnetic implantable hearing aid (RWEM) approach uses a magnet surgically implanted onto the round window membrane of the cochlea to impart vibrational energy to the inner ear when driven by a nearby electromagnetic coil. In this article, experimental methods used in animal ABR studies are described for this approach and evidence for the viability of this technique is demonstrated by the similarity of ABR waveforms obtained using RWEM and acoustically-evoked stimuli.