Hearing Loss (Deafness)

Anatomy of the ear

Hearing loss, or deafness, can be present at birth (congenital), or become evident later in life (acquired). The distinction between acquired and congenital deafness specifies only the time that the deafness appears. It does not specify whether the cause of the deafness is genetic (inherited).

Acquired deafness may or may not be genetic. For example, it may be a manifestation of a delayed-onset form of genetic deafness. Alternatively, acquired deafness may be due to damage to the ear due to noise or from other conditions.

Congenital deafness may or may not be genetic. In non-genetic causes, congenital deafness may be due to a condition or infection to which the mother was exposed during pregnancy, such as the rubella virus. Alternatively, congenital hearing loss may be associated with certain other characteristic findings. Fore example, a white forelock may be a sign of a genetic disease called Waardenburg syndrome that includes congenital deafness in the spectrum of disease. Overall, more than half of congenital hearing loss is inherited. 

Hearing loss can also be classified based on which portions of the hearing system (auditory system) are affected. When the nervous system is affected, it is referred to as sensorineural hearing loss. When the portions of the ear that are responsible for transmitting the sound to the nerves are affected, it is referred to as conductive hearing loss.

Conditions affecting the cochlea, eighth cranial nerve, spinal cord, or brain cause sensorineural hearing loss. Examples include:

• Meniere's disease,
• noise-induced hearing loss (such as prolonged or excessive exposure to loud music or machinery),
• hearing loss of aging (presbycusis),
• nerve injury from syphilis,
• hearing loss of unknown cause (idiopathic hearing loss),
• nerve tumors and;
• drug toxicity (such as aspirin and aminoglycosides).

Conditions that affect the ear canal, eardrum (tympanic membrane), and middle ear lead to conductive hearing loss. Examples of conductive hearing loss include:

• ear wax blocking the ear canal,
• otitis media and;
• otosclerosis.

Symptoms of hearing loss include mild loss of high frequency hearing, hearing loss associated with ringing or noises (tinnitus), and complete deafness. Symptoms may develop gradually over time with many causes of hearing loss.

People who are experiencing hearing loss may refrain from taking part in conversations, may turn the volume up high on the radio or TV, and may frequently ask others to repeat what they have said.

The treatment of hearing loss depends on its cause. For example:

• Ear wax can be removed
• Ear infection can be treated with medications
• Diseases that cause inflammation of the ear can be treated with medication
• Medications that are toxic to the ear can be avoided
• Occasionally surgical procedures are necessary