Transient-evoked otoacoustic emissions. Helpful tool in the detection of pseudohypacusis.

The object of the present study was to demonstrate the use of TEOAEs for diagnosing pseudohypacusis. Thirty-four patients were investigated for suspected pseudohypacusis based on the case history and clinical and audiological findings. TEOAEs confirmed the diagnosis in all cases except four patients with a pre-existing organic hearing loss exceeding 25-30 dB HL. All the remaining 30 patients showed normal TEOAE responses except four of the ears in which final assessment revealed hearing threshold lower than 30 dB in the middle frequency region. The method can be time-saving when performed at the first consultation. With its element of surprise, the patient can be confronted with the existence of a functional hearing loss. This frequently results in marked threshold improvement on repeat pure-tone audiometry.

Beta blockers and loss of hearing.

Loss of hearing in a 43 year old man during treatment with metoprolol was dose related and disappeared within a few months after the drug had been stopped. The hearing impairment was of mixed type, with an air bone gap without any disorder of the middle ear observable by conventional clinical methods. Similar scattered reports from international sources on loss of hearing during treatment with beta blockers are also presented.

Ototoxic effect of quaternary ammonium compounds.

In earlier investigations by the author it has been shown that chlorhexidine, when introduced into the middle ear of guinea pigs, caused serious damage to the inner ear. The present investigation was performed in order to study if the quaternary ammonium compounds benzethonium chloride and benzalkonium chloride, frequently used for skin disinfection, can also induce inner ear damage when introduced into the tympanic cavity of guinea pigs. The disinfectants in question, at a concentration of 0.1% and in a solution of aqua dest. or 70% alcohol, were introduced into the animals' middle ear for exposure times of 10, 30, or 60 min. The animals were sacrificed 2 or 9 weeks after the exposure and the organ of Corti and vestibular neuroepithelia were studied as surface preparations with phase contrast microscopy. It was found that most of the ears exposed to the disinfectants had suffered damage, affecting both the vestibular and cochlear parts of the inner ear. The extent of the damage was related both to the duration of exposure and to the length of the animals' survival after the exposure. Furthermore it was found that the tympanic cavity and the perilymphatic spaces of vestibulum and cochlea were pathologically changed.

Ototoxic effect of iodine disinfectants.

It had been suggested that disinfectants which could trickle into the middle ear through a perforated drum during the skin sterilization preceding otosurgery might cause inner ear damage resulting in deafness. In animal experiments it has been shown that chlorhexidine, benzethonium- and benzalkonium chloride, when introduced into the tympanic cavity of guinea pigs, will cause rather extensive damage to the neuroepithelial receptors of the inner ear. In the present study, iodine, frequently used for skin disinfection, has been investigated as regards ototoxicity by locally exposing the middle ear in guinea pigs. The duration of exposure was 10, 30, or 60 min. The animals were sacrificed 2 weeks later and the organs of Corti and neuroepithelial receptors of the vestibular part of the inner ear were studied as surface preparations in phase-contrast microscopy. It was found that slight damage had occurred in the basal parts of the organ of Corti of those ears exposed to iodine or iodophor in 70% alcohol for 60 or 30 min and damage to the vestibular receptors was observed in ears exposed to iodophor in 70% alcohol for 60 min. In ears exposed to iodine or iodophor in aqua dest., no damage to the inner ear sensory epithelia was revealed.

Cochlear damage from chlorhexidine in guinea pigs.

The disinfectant chlorhexidine has been extensively used as preoperative skin sterilizing agent. In the early 1970s it was suspected from clinical experience that inner ear damage with deafness might result from chlorhexidine accidentally introduced into the middle ear during preoperative skin disinfection. In order to study if chlorhexidine by local application in the middle ear has any ototoxic effect resulting in morphological changes in the organ of Corti, the tympanic cavity of guinea pigs was exposed to two different concentrations of the substance. Two different solvents were used and the duration of exposure was varied. The animals were sacrificed 2, 3, 4 or 10 weeks after exposure. In surface preparations of the organ of Corti, damage was seen in almost all exposed ears, related in extent to the concentration of chlorhexidine, the duration of exposure, and the time lapse after exposure. Furthermore, it was found that inner ear damage often extended beyond the organ of Corti and pathological changes were also observed in the mucosal lining of the tympanic cavity.

Vestibular damage from chlorhexidine in guinea pigs.

In the early 1970s the suspicion arose that chlorhexidine, a disinfectant extensively used for preoperative skin disinfection, was ototoxic if introduced into the middle ear cavity. It has previously been shown by the author that chlorhexidine causes damage to the organ of Corti of guinea pigs when introduced into the tympanic cavity. In the present study the toxic effect of chlorhexidine on the vestibular part of the inner ear is investigated. Middle ears of guinea pigs were exposed to chlorhexidine in two different concentrations in two different solvents. The duration of exposure was varied and the animals were sacrificed and examined at various periods. Damaged neuroepithelia were seen in most of the animals. The extent of damage was related to the concentration of chlorhexidine, to the duration of exposure and to the time lapse after exposure.

Structural changes in the organ of Corti of the guinea pig after obstruction of the arterial blood flow to the inner ear.

Forty-one young guinea pigs were studied after obstruction of the anterior inferior cerebellar artery in order to ascertain the effects on the surface specimen of the organ of Corti. Most of the animals had damage in the third and fourth turns (22) and a minority of these had dizziness and destruction nystagmus (3). Our hypothesis is that one of the causes of Meniere's disease is an interference with the inner ear circulation, and our plans for testing this hypothesis are given.