Sensorineural Hearing Loss

Sensorineural hearing loss is the most common type of permanent hearing loss. It occurs when there is damage to the inner ear (cochlea) or to the nerve pathways from the inner ear to the brain. Unlike conductive hearing loss, which involves problems with the outer or middle ear, SNHL involves an issue with the structures that convert sound vibrations into electrical signals that the brain interprets as sound, or with the transmission of those signals.

Here are the key points about sensorineural hearing loss:

Definition:

• It results from damage to the sensitive hair cells within the inner ear (cochlea) or to the auditory nerve (cochlear nerve) that transmits sound information to the brain.
• This damage is usually permanent because these sensory cells and auditory neurons typically do not regenerate naturally.

Main Causes:

The causes of sensorineural hearing loss are varied:

• Presbycusis: This is the most common cause, related to the natural aging of the ear. It manifests as a gradual, bilateral, and symmetrical hearing loss, usually affecting high-frequency sounds first.
• Noise Exposure: Loud and repeated noises (noisy work environments, loud music) or acute acoustic trauma (explosions, very loud concerts) can irreversibly destroy hair cells.
• Genetic Factors: Many cases of SNHL are hereditary and can be present at birth (congenital) or appear later in life.
• Infections: Certain viral infections (measles, mumps, cytomegalovirus) or bacterial infections (meningitis) can damage the inner ear or auditory nerve. Labyrinthitis (inflammation of the inner ear) can also be a cause.
• Diseases:
  • Ménière’s Disease: Characterized by vertigo, tinnitus, and fluctuating then progressive sensorineural hearing loss, often unilateral initially.
  • Acoustic Neuroma (Vestibular Schwannoma): A benign tumor developing on the auditory or vestibular nerve.
  • Certain autoimmune diseases.
• Ototoxic Drugs: Some medications (certain aminoglycoside antibiotics, loop diuretics, certain chemotherapy drugs like cisplatin, high-dose aspirin) can be toxic to the inner ear.
• Head Trauma: A fracture of the temporal bone (the bone surrounding the inner ear) or severe trauma can damage auditory structures.
• Vascular Causes: Poor blood circulation to the inner ear can cause damage (e.g., in cases of sudden sensorineural hearing loss).
• Other Factors: Diabetes, hypertension, and smoking can be risk factors or aggravating factors.

Common Symptoms:

Symptoms can vary depending on the cause and degree of hearing loss:

• Difficulty hearing and understanding speech: Especially in noisy environments or during group conversations. People with SNHL often feel that others are mumbling.
• Difficulty perceiving high-pitched sounds: Such as a telephone ringing, birds singing, or the voices of children or women.
• Tinnitus: Perception of ringing, buzzing, or other noises in the ears or head.
• Need to turn up the volume of the television or radio.
• Difficulty localizing the source of sounds.
• Sometimes, dizziness or balance problems, especially if the vestibular system (the part of the inner ear responsible for balance) is also affected.
• In some cases, hyperacusis (intolerance to normally bearable sounds) may be present.

Diagnosis:

The diagnosis is made by an ENT (Ear, Nose, and Throat) doctor, also known as an otolaryngologist, and is based on:

• Medical History: Discussion about symptoms, medical and family history, noise exposure, etc.
• Otoscopic Examination: To check the condition of the external ear canal and eardrum.
• Audiometric Tests:
  • Pure-Tone Audiometry: Measures hearing thresholds for different frequencies (pure tones) via air conduction (sounds passing through the ear canal) and bone conduction (vibrations transmitted directly to the skull bone). In SNHL, both air and bone conduction thresholds are lowered and close to each other.
  • Speech Audiometry: Assesses the ability to understand speech at different sound levels.
• Other tests may be necessary to determine the cause (e.g., Auditory Brainstem Response – ABR, Otoacoustic Emissions – OAEs, imaging like MRI if a neuroma is suspected).

Treatments and Management:

Sensorineural hearing loss is generally irreversible because the damaged sensory cells do not regenerate. Therefore, management primarily aims to compensate for the hearing loss and improve communication:

• Hearing Aids: This is the most common solution. They amplify sounds to make them audible and can be adjusted to target lost frequencies. Various types of hearing aids are available (behind-the-ear, in-the-ear).
• Cochlear Implants: Considered for severe to profound bilateral SNHL when hearing aids are no longer sufficiently effective. A cochlear implant directly stimulates the auditory nerve.
• Auditory Rehabilitation / Speech Therapy: Can be helpful for learning to make better use of remaining hearing, for lip-reading, or for children to develop language.
• Specific Treatments for the Cause:
  • For sudden sensorineural hearing loss, corticosteroids or vasodilators may sometimes be prescribed urgently.
  • Treating an underlying disease (like Ménière’s disease or a tumor) is essential.
• Prevention: Very important to prevent worsening or onset of noise-induced hearing loss (wearing hearing protection) and to manage risk factors (controlling diabetes, hypertension).

If you suspect you have sensorineural hearing loss, it is essential to consult an ENT doctor for an accurate diagnosis and appropriate management plan. “Surdité de perception” in English is Sensorineural Hearing Loss (SNHL).

It is the most common type of permanent hearing loss. It occurs when there is damage to the inner ear (specifically the cochlea, which contains tiny hair cells that convert sound vibrations into nerve signals) or to the nerve pathways from the inner ear to the brain (the auditory nerve).

Here’s a breakdown of what that means:

How it Differs: Unlike conductive hearing loss, which involves problems with the outer or middle ear conducting sound to the inner ear, sensorineural hearing loss means the inner ear structures or the nerve itself are not functioning correctly to transmit sound information to the brain for interpretation.

Common Causes of Sensorineural Hearing Loss:

• Aging (Presbycusis): This is the most common cause. It’s a gradual decline in hearing that happens as people get older.
• Noise Exposure (Noise-Induced Hearing Loss – NIHL): Prolonged exposure to loud noises (e.g., in a noisy workplace, from loud music, machinery) or a single exposure to an extremely loud sound (e.g., an explosion) can damage the sensitive hair cells in the cochlea.
• Genetics: Some forms of SNHL are hereditary and can be present at birth or develop later in life.
• Ototoxic Medications: Certain drugs can damage the inner ear. Examples include some strong antibiotics (like aminoglycosides), certain chemotherapy drugs (especially platinum-based ones like cisplatin), and high doses of aspirin.
• Illnesses and Infections: Viral infections (like measles, mumps, meningitis, rubella, cytomegalovirus) or bacterial infections can affect the inner ear.
• Head Trauma or Acoustic Trauma: A severe blow to the head or a sudden, very loud noise can cause immediate and permanent damage.
• Ménière’s Disease: A disorder of the inner ear that can cause fluctuating hearing loss, tinnitus (ringing in the ears), vertigo (dizziness), and a feeling of fullness in the ear.
• Acoustic Neuroma (Vestibular Schwannoma): A non-cancerous tumor that can develop on the auditory nerve.
• Autoimmune Inner Ear Disease: When the body’s immune system mistakenly attacks the inner ear.
• Vascular Problems: Issues with blood supply to the inner ear.
• Congenital Factors: Issues during fetal development or complications at birth.

Common Symptoms:

• Difficulty hearing sounds, especially soft or high-pitched sounds (like women’s or children’s voices, birds singing).
• Speech may sound muffled or unclear; people might seem to be mumbling.
• Difficulty understanding conversations, particularly in noisy environments.
• Tinnitus (ringing, buzzing, hissing, or roaring sounds in the ears).
• Sometimes, dizziness or balance problems can accompany SNHL, especially if the vestibular system (also in the inner ear) is affected.
• Needing to turn up the volume on the TV or radio.

Diagnosis:

An audiologist or an ENT (Ear, Nose, and Throat) doctor, also known as an otolaryngologist, will typically diagnose SNHL through:

• Medical History and Physical Examination: Including an otoscopy to look into the ear canal.
• Hearing Tests:
  • Pure-tone Audiometry: Measures the softest sounds you can hear at different pitches (frequencies). In SNHL, both air conduction (sound through the ear canal) and bone conduction (sound through skull vibration) thresholds will be similarly reduced.
  • Speech Audiometry: Assesses your ability to hear and understand spoken words.
• Other tests like otoacoustic emissions (OAEs) or auditory brainstem response (ABR) testing might be used, especially in infants or to differentiate types of SNHL.

Treatment and Management:

Sensorineural hearing loss is generally permanent because the damaged hair cells in the cochlea or nerve fibers do not regenerate in mammals (including humans). Treatment focuses on managing the hearing loss and improving communication:

• Hearing Aids: These are the most common treatment. They amplify sounds to make them more audible.
• Cochlear Implants: For individuals with severe to profound SNHL for whom hearing aids provide little or no benefit. A cochlear implant bypasses the damaged parts of the inner ear and directly stimulates the auditory nerve.
• Assistive Listening Devices (ALDs): Devices like FM systems, amplified telephones, or personal amplifiers can help in specific listening situations.
• Auditory Rehabilitation and Communication Strategies: This can include speech reading (lip reading), learning communication strategies, and counseling.
• Treatment of Underlying Causes (if applicable):
  • For sudden sensorineural hearing loss (SSNHL), prompt treatment with corticosteroids can sometimes result in partial or full recovery.
  • Managing conditions like Ménière’s disease or autoimmune disorders.
• Prevention: Protecting ears from loud noise is crucial to prevent noise-induced SNHL or further damage.

If you suspect you have sensorineural hearing loss, it’s important to see a healthcare professional for proper diagnosis and guidance.