Sensorineural Hearing Loss: Series from Maryville University

There are currently 466 million people experiencing hearing loss worldwide, according to the World Health Organization, and an estimated 900 million people will have hearing loss by the year 2050. Some 60% of childhood hearing loss results from preventable causes, and 1.1 billion people between the ages of 12 and 35 are at risk of hearing loss due to noise exposure. The annual global cost of untreated hearing loss, in U.S. dollars, is $750 billion.

Sensorineural Hearing Loss

More than 90% of all hearing loss in adults is sensorineural hearing loss, according to Healthline. Some people refer to SNHL as “nerve deafness,” although this term does not account for SNHL issues involving damage to the tiny hairs in the cochlea called stereocilia.

What is sensorineural hearing loss?

Damage to the auditory nerve or the structures of the inner ear can lead to sensorineural hearing loss. The stereocilia convert vibrations from sound into signals for the auditory nerve and brain, and injury to the stereocilia causes SNHL.

SNHL can range from mild hearing loss to profound deafness, depending on the damage to the stereocilia. Exposure to sounds louder than 85 decibels, the equivalent to heavy traffic noise heard from inside a vehicle, can harm the stereocilia.

Causes of sensorineural hearing loss

Nerve damage to the inner ear’s structures — created by loud noises, genetics, or aging — can cause SNHL.

Congenital sensorineural hearing loss

SNHL that is congenital, or present from birth, is one of the most common birth abnormalities. Congenital SNHL affects between one and three babies per 1,000, according to a StatPearls report. Genetics causes about half of congenital hearing loss cases, with environmental factors causing the other half. Infections and a lack of oxygen are among the environmental causes of congenital hearing loss.

Loud noises and sensorineural hearing loss

Even one-time exposure to sounds over 85 decibels — such as gunshots or explosions — can cause SNHL. Hearing loss may not be noticeable until damage occurs to 30% to 50% of the ear’s stereocilia, according to Healthline.

Age and sensorineural hearing loss

Age-related SNHL, known as presbycusis, is one of the most common conditions affecting older adults. Presbycusis typically occurs in both ears, affecting both equally. This type of hearing loss is gradual and often results from changes to the inner ear as a person ages, although other changes related to the ear and brain as well as certain medical conditions and medicines can be a factor.

Additional causes of sensorineural hearing loss

Healthline reports that SNHL has more than 100 potential causes. Among the additional causes for sensorineural hearing loss are:

• Head trauma
• Ménière’s disease, an inner ear disorder
• Otosclerosis, abnormalities that develop in bone tissue
• Lyme disease, a disease often transmitted through tick bites
• Tumors

Symptoms of sensorineural hearing loss

Sensorineural hearing loss can occur in one or both ears, depending on the cause. The hearing loss may develop gradually or suddenly, within several days.

• Bilateral sensorineural hearing loss — Occurring in both ears, this type of SNHL can be the result of genetics, exposure to loud sounds, and diseases such as measles.
• Unilateral sensorineural hearing loss — This type of SNHL, which affects both ears, can be the result of a tumor, Ménière’s disease, or a sudden loud noise in one ear.
• Asymmetrical sensorineural hearing loss — Asymmetrical SNHL occurs in both ears, but with one side experiencing more hearing loss than the other.

Signs of sudden sensorineural hearing loss

Individuals with sudden SNHL often notice symptoms upon waking. The symptoms of sudden SNHL include the following:

• Trouble hearing sounds when there’s background noise
• Difficulty understanding children’s and female voices
• Dizziness or balance problems
• Trouble hearing high-pitched sounds
• Sounds and voices sound muffled
• Hearing voices but not understanding them
• Tinnitus, or ringing in the ears