Conductive and Sensorineural Hearing Loss and deafnes for students preparing for the USMLE.
CONDUCTIVE HEARING LOSS DEAFNESS
Conductive hearing loss invovles the part of the ear ranging from stapes to outer ear. Rinne’s Test is negative meaning the bone conduction is greater than air conduction. Weber’s test lateralizes to the bad ear. Absolute bone conduction will be normal. Pure tone audiometry will show normal bone conduction and the air conduction will be lower than 10 decibels known as the AB Gap. Rarely goes below 60 decibels.
Congenital causes include, meatal atresia, ossicular discontinuity, stapes fixation. Acquired causes include obstruction such as ear wax and foriegn body. Tympanic membrane perforation, infection. Ossicle fixation or disruption of the ossicles. Eustuchian tube may also cause.
SENSORINEURAL HEARING LOSS DEAFNESS
Sensorineural hearing loss involves cochlea and cranial nerve 8. Rinne’s test is positive meaning air conduction is greater than bone conduction. Weber’s test lateralizes to the good ear. Absolute bone conduction in sensorineural is decreased. Pure tone audiometry in sensorineural hearing loss will show drop in the higher frequencies and there will not be a large ab gap, but goes below 60 decibels. Speech discrimination will be poor in sensorineural hearing loss.
Acquired causes include labyrinthitis, physical trauma, noise trauma, acoustic neuroma, presbycusis, Meniere‘s disease, drugs, systemic diseases (DM, Hypothyroidism), renal syndrome, autoimmune diseases, blood dyscrasias and multiple sclerosis.
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