Acute changes in cochlear potentials due to cisplatin.

The purpose of this study was to investigate how the hair cells and stria vascularis are affected at the onset of cisplatin ototoxicity. The effects on the endocochlear potential (EP) and the cochlear microphonics (CM) were observed simultaneously in two groups of adult chinchillas receiving as follows: (1) 5 microl of cisplatin (1 mg/ml) in normal saline, and (2) 5 microl of normal saline on the round window. The EP and the CM were recorded for 12-14 h after cisplatin application, and morphological changes were assessed using scanning electron microscopy. Both the EP and the CM amplitude demonstrated a profound reduction, and a very strong correlation was observed between these two values during this time period. Although the reduction of the EP and the CM was observed by 12-14 h, only very slight degeneration of outer hair cells was seen at that time. These data suggested that a reduction of the EP which was caused by the alteration of the stria vascularis might be primarily responsible for very early changes in cochlear function after topical cisplatin application, while later changes were the direct result of hair cell damage.

Electrocochleographic evaluation of hearing loss in acoustic neuromas.

OBJECTIVE: This study aimed to clarify the pathophysiology involved in the cause of hearing impairment due to acoustic neuromas (AN) with electrocochleograph (ECoG). STUDY DESIGN: The study design was a retrospective case study. SETTING: This study was conducted in a tertiary referral center. PATIENT: Thirty-four patients diagnosed as having AN by magnetic resonance imaging between 1988 and 1995. INTERVENTION: Diagnostic. MAIN OUTCOME MEASURES: The authors made a comparison between the patients' ECoG findings and the size of their tumors as determined by magnetic resonance imaging and a pure-tone audiometry (PTA). The disparity between the threshold of PTA and the detective threshold of compound action potential (CAP) or that of the cochlear microphonics (CM) was calculated. When the threshold of the PTA was worse than the detective threshold of the CAP or the CM, the disparity was regarded as indicating a hearing loss of retrocochlear origin. RESULTS: There was no correlation found between tumor size and the detective threshold of CAP or CM. Disparity was found to correlate with tumor size. CONCLUSIONS: These findings seem to indicate that retrocochlear damage in AN increases parallel to the growth of the tumor and that retrocochlear damage can be detected by the ECoG before surgery.

[Electrocochleographic study of acute low-tone sensorineural deafness].

We assessed 53 patients with acute low-tone sensorineural deafness (LTSD) over the past 10 years using the transtympanic-electrode technique of electrocochleography. The audiometric diagnostic criteria were as follows: Average hearing level at the lower two frequencies (250, 500Hz) greater than 30 dB, and of the higher three frequencies (2, 4, 8kHz) less than 20 dB. Patients were divided into three groups on the basis of their electrocochleographic findings; 33 cases of the endolymphatic hydrops type, 17 cases of the hair cell damage type and 3 cases of the neural damage type. The outcome of these patients was assessed together their electrocochleographic findings. The results obtained were as follows: 1) Most of the improved cases were of the endolymphatic hydrops type and in females in their twenties. All of the improved cases showed high AP and -SP amplitude, but not dominant -SP, and exhibited slight prolonged AP latency. Satisfactory CM responses at 500 Hz were also found. 2) Most of the hair cell damage type exhibited no change, and some unrecovered cases of the endolymphatic hydrops type progressed to Meniere's disease.