Ear Care/Otology - Neurotology

By definition the exact cause of sudden SNHL is literally unknown cause. Current research is underway to determine the cause of sudden hearing loss as well as potential cures. Some of the proposed causes are listed below. The most commonly proposed causes of sudden SNHL include:

• viral infection of the inner ear,
• blood flow abnormalities to the inner ear, and
• problems with the fluid mechanics of the inner ear which leads to tears in the fine membranes of the cochlea.

Viral Infection 

Perhaps the most common theory to explain sudden hearing loss is a viral infection. Evidence of viral infections have been found by researchers in patients who have had sudden SNHL, which is why viral infection is suspected. A viral infection can cause inflammation of the inner ear or auditory nerve. This inflammation of the inner ear structure and associated blood vessels can cause hearing loss. No pain, fever, muscle cramps, or other signs of a viral illness are usually encountered. Occasionally, signs of an upper respiratory infection may precede the onset of sudden SNHL.

Cochlear Membrane Tears 

The cochlea or inner ear is made of fine, delicate membranes that contain fluid-filled spaces. It is the movement of the fluid in these spaces that creates sound. Particular electrolytes are in these fluid filled spaces. This active storage of electrolytes creates different charges (+ or -) in these fluid-filled spaces separated by the fine membranes. This charge difference, or potential, between the spaces allows for the generation of a nerve impulse much in the same way a battery with its positive and negative poles can induce electricity.

A tear in the fine delicate membranes can lead to a mixing of the fluid, a loss in the potential, and an inability to generate a nerve impulse. This inability to generate a nerve impulse leads to a hearing loss. Tears in the membrane can occur from pre-existing defects (probably hereditary) and from excessive fluid in the spaces such as Meniere’s disease (see Meniere’s disease section).

Blood Flow Abnormalities

Another potential cause for hearing loss is abnormal blood flow to the cochlea. Severe hypertension may lead to bleeding in the inner ear with resulting hearing loss. Poor blood flow from arteriosclerosis may lead to inadequate perfusion or flow of blood into the cochlea. These mechanisms may be described as a stroke of the inner ear. This cause is more commonly found in the elderly, but may also be associated with the use of birth control pills in the younger population.

Intra-Cochlear Membrane Tears 

A tear in one of the fine membranes that makes up the inner ear. May be the cause of hearing loss in Meniere’s disease.

Other Potential Causes of Sudden SNHL

• Bacterial infection, such as Otitis media, syphilis
• Vascular occlusion (from stroke)
• Vasculitis or inflammation of the blood vessels
• Meniere’s disease or inner ear fluid build up
• Labyrinthitis, (viral or bacterial inner ear infection)
• Meningitis (viral or bacterial infection of brain lining)
• Medical disorders, such as diabetes, hypo- or hyperthyroidism
• Hereditary disorders, such as inner ear hereditary hearing loss, Usher’s syndrome, Waardenburg’s syndrome
• Low levels of oxygen (hypoxia) (from stroke)
• Medications, such as antibiotics, (termed ototoxic medications)
• Malignant neoplasm (tumors or cancer of the ear)
• Benign neoplasms (tumors), such as acoustic neuroma, meningioma
• Autoimmune hearing loss: immune system disorder that can affect the inner ear as rheumatoid arthritis is an immune system disorder that affects the joints
• Cholesteatoma or chronic middle ear infection can also cause an inner ear loss in advanced cases
• Otosclerosis or fixation of hearing bones, can also cause an inner ear loss
• Hypertension, which may cause bleeding in the inner ear or brain