Evidence of subtle auditory deficit in a group of patients recovered from bacterial meningitis.
OBJECTIVE
Sensorineural hearing loss of greater than 30 dB hearing loss occurs in up to 30% of patients after acute bacterial meningitis. This study investigated whether postbacterial meningitic patients with no apparent clinical sensorineural hearing loss had any evidence of more subtle subclinical cochlear deficit.


METHODS
Prospective case-controlled clinical trial.


METHODS
Departments of Otolaryngology in Leicester and Nottingham, England, UK.


METHODS
Fifty-eight controls and 20 postbacterial meningitic patients aged between 18 and 38 years were screened by a questionnaire and tympanometry to exclude hearing loss attributable to other causes. All participants fell below the 90th percentile pure-tone audiometry threshold of the Lutman and Davis UK data sets.


METHODS
In both ears, standard (0.25-8 kHz) pure-tone audiometry, high-frequency pure-tone audiometry (10-16 kHz), and distortion product otoacoustic emissions at 2, 4, and 6 kHz were measured.


RESULTS
Mean thresholds over the range of standard pure-tone audiometry (analyzed independently) for the postbacterial meningitic patients were significantly elevated at most frequencies (p < 0.05-p < 0.001) between 4 and 7 dB in both ears above control group values. There was no evidence of significant high-frequency threshold elevation (10-16 kHz). The mean iso-distortion product values at 2, 4, and 6 kHz were elevated in both ears in the meningitis group; significantly so (p < 0.05-p < 0.01) at all three frequencies in the right ear and at 4 kHz in the left.


CONCLUSIONS
Postbacterial meningitic patients with hearing below the 90th percentile range had a slight but significant subclinical threshold elevation over the standard pure-tone audiometry. This may reflect a real effect of the infection at the level of the cochlea, or it may be attributable to a mild residual cognitive defect. The moderate increases in iso-distortion product values are more likely to be real and reflect an effect on outer hair cell function in response to lower stimulus intensities.
Mulheran
Mike
M
Medical Research Council, Center for Mechanism of Human Toxicity, Leicester University, Leicester, England, UK. mm22@le.ac.uk
Wiselka
Martin
M
Johnston
Mark N
MN
D000158:Acoustic Impedance Tests; D000293:Adolescent; D000328:Adult; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold; D016022:Case-Control Studies; D003051:Cochlea / Q000503:physiopathology; D005260:Female; D006319:Hearing Loss, Sensorineural / Q000209:etiology*; D006801:Humans; D008297:Male; D016920:Meningitis, Bacterial / Q000150:complications*; D017084:Otoacoustic Emissions, Spontaneous; D011446:Prospective Studies; D011795:Surveys and Questionnaires