Sensorineural hearing loss

Sensorineural hearing loss (SNHL) occurs due to disease of the inner ear or the hearing nerve.  Such hearing loss may be a result of genetic disorders but in most cases the damage to the inner ear or the nerve is secondary to aging, noise, drugs, or disease.  Such a hearing loss may be partial or total.  This type of hearing loss is generally not correctable by either medications or surgery.  Persons with this type of hearing loss are more incapacitated than those with conductive hearing loss.  These individuals can sometimes hear sounds but have difficulty in understanding speech because of poor discrimination.  Sometimes such losses can  occur suddenly.  They are usually unilateral and caused by a viral infection of the inner ear or a clot in the internal auditory artery.  Other causes of sudden deafness is due to exposure to loud sounds (firecrackers or explosives), fracture of the temporal bone.

Both Sensorineural and conductive hearing losses may be congenital (present at birth) or delayed. Both types may result from either genetic or acquired factors such as disease or injury.  Hearing loss with both conductive and sensorineural elements is called as mixed hearing loss.

SNHL in infants may be due to genetic causes or non genetic causes.  Genetic causes should be identified because the affected families need genetic counselling.  Non genetic causes of hearing loss in infants include maternal use of ototoxic drugs, viral infections that affect the fetus (maternal rubella), metabolic disorders (cretinism), Rh incompatibility, irradiation in the first trimester, prematurity, fetal distress, low birth weight, hyperbilirubinaemia, bacterial meningitis and anatomic malformations of the head and neck.  The most prominent signs of deafness in infants are the lack of startle reflex and delay in acquiring speech.  Totally deaf children do not learn to speak because they cannot hear speech.   The need to hear is very important for development of speech.  Early detection and treatment  of hearing impairment in infants are essential for acquiring the ability to speak.

SNHL in adults may also occur due to genetic aberrations or from acquired causes such as aging trauma or disease.   Familial progressive sensorineural loss (genetic) and presbyacusis (acquired) are common types of delayed sensorineural loss. Presbyacusis is a progressive loss of hearing acuity that occurs with advancing age.  Acquired SNHL may also result from infections caused by bacteria or viruses (measles & mumps), ototoxic drugs, neoplastic diseases, temporal bone fractures damaging the cochlea, Meniere’s disease, hypothyroidism, vascular insufficiency and central nervous system  disorders like multiple sclerosis.

Deafness resulting from SNHL is permanent and there is no medical or surgical cure in most of the cases.  Using a hearing aid or a cochlear implant in selective cases may benefit those suffering from this type of HL.