Classification of hearing impairment

What it is

Hearing impairment is classified into three:

• Conductive hearing loss, where any cause interferes with the conduction of sound to reach the cochlea.
• Sensorineural hearing loss, which comes from the inner ear, the cochlea or the auditory nerve.
• Mixed hearing loss, a combination of conductive and sensorineural hearing loss.

Causes and risk

Conductive causes are otitis media effusion, cerumen, otomycosis, acute suppurative otitis media, perforated drum, chronic suppurative otitis media, otosclerosis, glomus benign tumors, keratosis and osteoma. Excess earwax is a common cause of conductive hearing loss.

Sensorineural causes are Meniere's disease, presbyacusis, noise induced hearing loss, ototoxicity, temporal bone fracture and acoustic neuroma. The majority of sudden-onset sensorineural hearing loss is idiopathic.

Some causes carry their own pattern. Otosclerosis is a genetic condition, inherited in an autosomal dominant fashion, which causes irregular bony formation in the middle ear and dysfunction of the ossicular chain; it gives bilateral conductive pattern hearing loss with tinnitus, typically presents in middle age, and is progressive. Presbyacusis gives a sensorineural, high frequency hearing loss and is unlikely in a young patient. Noise damage gives a sensorineural hearing loss, worst in the range of 3000-6000Hz. Acoustic neuromas are usually unilateral, cause sensorineural hearing loss, and tend to occur gradually.