Definition

Sensorineural hearing loss is a type of hearing loss caused by damage to the inner ear structures or the auditory nerve. This condition accounts for over 90 percent of hearing loss in adults. Under normal circumstances, the inner ear's spiral-shaped cochlea contains tiny hair cells called stereocilia. These hairs convert sound wave vibrations into nerve signals transmitted by the auditory nerve to the brain. Exposure to sounds louder than 85 decibels can damage these hair cells (85 decibels is approximately the sound level of heavy traffic heard inside a car). However, hearing loss might not occur if the damage to these hair cells is less than 30 to 50 percent.

The impairment that occurs in sensorineural hearing loss is typically permanent. The severity of sensorineural hearing loss varies depending on the extent of the damage:

• Mild hearing loss, the hearing loss is between 26 and 40 decibels.
• Moderate hearing loss, the hearing loss is between 41 and 55 decibels.
• Severe hearing loss, the hearing loss is greater than 71 decibels.

Causes

Sensorineural hearing loss results from damage to the tiny hair cells in the inner part of the ear or the auditory nerve. The causes of this damage can be categorized as either acquired or congenital.

Acquired 

Hearing loss that develops after birth, typically later in life. This type can be caused by various factors, such as:

• Aging: Age-related hearing loss, or presbycusis, is one of the most common causes. Hearing loss develops over time as the function of the auditory nerve diminishes. This condition usually affects both ears and can be difficult to detect initially.
• Noise: Noise-induced hearing Loss (NIHL) can result from a single exposure to extremely loud sounds, such as explosions or gunshots, or prolonged exposure to sounds above 85 decibels.
• Infection: Viral infections like measles, meningitis, and mumps can lead to sensorineural hearing loss.
• Head injury or acoustic trauma: Exposure to very loud sounds, such as bomb explosions, or physical trauma to the head can damage the inner ear. Many military veterans experience sensorineural deafness due to battlefield noise.
• Sudden changes in air pressure: Activities such as scuba diving or flying on an airplane can cause inner ear fluid shifts, leading to leaks or ruptures that damage inner ear nerves.
• Tumors: Some tumors, such as acoustic neuroma and cholesteatoma (abnormal growth of skin in the middle ear), can affect the nerves transmitting signals between the inner ear and the brain.
• Drugs: Over 200 drugs and chemicals are ototoxic and can cause hearing damage. Some, including certain antibiotics, anti-inflammatory drugs, and chemotherapy agents, can cause permanent hearing loss.
• Other diseases: Conditions like autoimmune diseases (e.g., lupus), thyroiditis, Meniere's disease, central nervous system disorders, structural ear abnormalities, and otosclerosis (abnormal bone growth in the middle ear) can impair hearing.

Congenital 

Congenital sensorineural hearing loss that occurs during pregnancy is much rarer than acquired sensorineural hearing loss. The causes include prematurity, maternal diabetes, oxygen deprivation at birth, genetic factors, and infectious diseases passed from mother to child in utero, such as rubella.

Risk factor

Several factors can damage the hair and nerve cells in the inner ear, including:

• Aging. The function and structure of the inner ear deteriorate with age.
• Exposure to loud noises. Long-term exposure to loud noises or short bursts of high-intensity sounds (e.g., gunshots, and explosions) can damage inner ear cells.
• Genetics. A family history of hearing loss may increase susceptibility to noise-related or age-related ear damage.
• Occupational noise. Working in noisy environments, such as farming, construction, or factories, can damage the inner ear.
• Recreational noise. Exposure to loud sounds from certain activities such as shooting firearms and jet engines can cause immediate, permanent hearing loss. Other activities such as snowmobiling, motorbiking, using loud woodworking tools, or listening to loud music can also play a part in hearing loss occurrence.
• Certain medications. Drugs like the Gentamicin antibiotic, Sildenafil (Viagra), and specific chemotherapy agents can harm the inner ear.
• Certain diseases. Conditions like autoimmune diseases or central nervous system disorders can lead to sensorineural hearing loss.

Symptoms

Symptoms of sensorineural hearing loss include:

• Dizziness or balance problems
• Tinnitus (ringing in the ears)
• Frequently asking others to repeat themselves
• Difficulty in communicating on the phone
• Trouble hearing conversations in noisy environments, such as parties, restaurants, or markets
• Fatigue
• Social withdrawal due to difficulty hearing others

Diagnosis

To diagnose sensorineural hearing lodd, the doctor will begin with an interview to discuss your symptoms and any potential risk factors you have. A physical examination, particularly of the ears, will follow to identify signs of inflammation, fluid or earwax buildup, eardrum damage, and any foreign objects in the ears. This helps differentiate sensorineural deafness from other types of hearing loss. Initial screening with a tuning fork includes:

• Weber's test. The doctor strikes a 512 Hz tuning fork and places it in the center of your forehead. If the sound is louder in the healthy ear, it suggests sensorineural hearing loss.
• Rinne test. The doctor places a struck tuning fork on the mastoid bone (behind the ear) until you no longer hear it, then moves it in front of the ear canal. In sensorineural deafness, the sound is heard better in front of the ear canal than on the bone.

An audiometry test is often recommended for a detailed assessment of suspected hearing loss. During this test, you will wear headphones in a soundproof booth, with tones and words will be played at different volumes and frequencies to determine the smallest sounds you can hear and the specific frequencies of your hearing loss.

Management

The management of sensorineural hearing loss is limited, as this type of hearing loss is typically permanent. Common treatments to help in accommodating the remaining hearing function include:

• Hearing aids: These devices can be tailored to your hearing loss, enhancing certain frequencies without affecting others.
• Cochlear implants: For severe sensorineural deafness, a cochlear implant can be surgically implanted. It consists of a microphone worn behind the ear and a device in the ear that sends electrical signals to the auditory nerve.

Complications

Sensorineural hearing loss is permanent and can significantly impact daily activities and quality of life. Individuals with hearing loss may experience depression due to communication difficulties and feelings of isolation from their surroundings.

Prevention

To prevent damage to hair and nerve cells in the inner ear, consider the following measures:

• Keep headphone volume below 60 percent and lower the volume of loud sounds.
• Use earplugs or protective equipment in noisy environments.
• Avoid high-risk activities that could expose you to loud noises, such as snowmobiling, hunting, using power tools, or attending loud concerts.

When to see a doctor?

Consult your doctor if you experience symptoms of hearing loss, balance issues, or tinnitus to determine the underlying cause.

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