ABSTRACT
OBJECTIVE: The assessment of bone conduction thresholds in patients with conductive hearing loss is not a full measure of the function of the inner ear due to the weakening of the influence of middle ear components on bone conduction. This relationship has been called the 'Carhart effect'. METHODS: The retrospective analysis covered 977 patients diagnosed and treated for middle ear diseases from 2010 to 2020. The Carhart effect was considered to be an increase in the bone conduction threshold by a minimum of 10 dB relative to adjacent frequencies. The study was performed with the aim of assessing the presence of the Carhart effect in the course of middle ear diseases in pretreatment analysis. RESULTS: The Carhart effect was observed in 532 cases, most often in patients with chronic otitis media and otosclerosis. It was least often observed in patients with otitis media with effusion. In otitis media with effusion, the Carhart effect was more often noted for the frequency of 4000 Hz, in otosclerosis for the frequency of 2000 Hz. In patients with chronic otitis media, this effect for the frequency of 4000 Hz was correlated with the location of inflammatory changes in the attic area. The presence of inflammatory lesions in the oval window area was associated with the presence of the Carhart effect for the frequency of 2000 Hz. CONCLUSIONS: 1. The frequency of the Carhart effect observed in diseases of the middle ear does not depend on the disease entity but on the type and location of abnormalities in the middle ear. 2. The Carhart effect observed for the frequency of 4000 Hz coexists with the localization of lesions in the range of the malleus and incus, and for the frequency of 2000 Hz, it is partially associated with abnormalities in the range of stapes and oval window.
ABSTRACT
Relation between chronic otitis media and sensorineural hearing loss is controversial. Otitis media can cause threshold shift in high frequency range. Also this correlation with patient's age, disease duration and normal ear is of importance for early prevention of hearing loss. The aim of this study was to evaluate relationship between sensorineural hearing loss and chronic otitis media. We also studied association of bone conduction between diseased ear and contralateral normal ear. In this study, 840 patients of unilateral COM were included. Audiometry was done and data analyzed. Majority of patients showing SNHL had COM for over a period of 5 years. Squamosal disease showed early progression to SNHL than mucosal disease. Higher frequencies were found to be more affected and maximum bone gap was seen at 4000 Hz. There was significant difference in mean bone conduction threshold between diseased ear and normal ear at all frequencies (p value < 0.001). Contradicting studies have emerged about association of SNHL with COM. Studies suggest that SNHL does not change with age but with duration. Bone conduction threshold tends to increase with increasing frequency. Few authors also pointed that this may be due to Carhart's effect and not due to disease damaging inner ear.
ABSTRACT
The objective is to evaluate change in post-operative bone conduction in patients who underwent surgery for conductive/mixed hearing loss due to various reasons. The study design is of retrospective case review and tertiary referral center setting. Five-hundred patients with unilateral conductive/mixed hearing loss were divided into five equal groups (each representing different causes for pre-operative hearing loss), who underwent appropriate surgical correction and had a follow-up audiogram available. The intervention comprises surgery (like myringoplasty and ossiculoplasty with closed or open cavity mastoidectomy for chronic otitis media, stapes mobilization for tympanosclerosis and stapedotomy for otosclerosis) for conductive/mixed hearing loss. Significant improvement or worsening in bone conduction was defined as 15 dB or more improvement or worsening of bone conduction threshold at least in two frequencies between 500 and 4000 Hz. All the other groups also showed a consistent pre-operative bone conduction reduction with an equally consistent improvement in post-operative bone conduction improvement to a varying degree with otosclerosis group having maximum percentage of patients with post-operative bone conduction improvement (60%). The measurement of bone conduction is not necessarily a true reflection of the function of the inner ear. Middle ear makes a contribution to bone conduction and correction of a middle ear conductive lesion causes an apparent improvement in inner ear function. The apparent inner ear hearing loss caused in this way may be reversible to some extent.
