What Is Bilateral Hearing Loss? Understanding the Mechanics. 

Bilateral hearing loss refers to hearing loss that occurs in both ears. It can result from pathologies affecting the middle or outer ear structures simultaneously, leading to bilateral conductive hearing loss. However, bilateral sensorineural hearing loss is more common, particularly in adults, and should be the primary diagnostic consideration in most clinical contexts.

Bilateral Conductive Hearing Loss 

Bilateral, conductive hearing loss occurs when a pathology affects the middle or outer ears of both ears at the same time. This prevents the sound from getting through to the inner ear properly. Examples of pathologies where this can happen include: 

• Ear infections/fluid in the ears
• Perforated tympanic membranes
• Otosclerosis
• Ear wax build-up

Bilateral conductive hearing loss can often be treated using medical management. For example, ear infections can be treated with antibiotics, and ear wax build-up can be treated by removing the wax. Small children are particularly prone to ear infections and fluid in their ears due to anatomical differences with smaller heads; however, they usually grow out of being susceptible to these issues. In cases where medical management is not suitable or unsuccessful, these patients may be fitted with hearing devices to mitigate the effects of their bilateral hearing loss. 

Patients with bilateral sensorineural hearing loss may notice hearing is generally more difficult, particularly in more challenging listening environments. Sensorineural bilateral hearing loss tends to affect the high frequencies first, often creating symptoms like feeling like the speaker is mumbling, turning the TV or radio up, difficulty hearing on the phone, and difficulty following a conversation in noise. 

Bilateral hearing loss can have many different causes. The shape of the hearing loss with bilateral hearing loss can vary. This means how it affects your patients' hearing will vary depending on the cause and the shape of the hearing loss.

The most common type of bilateral hearing loss, particularly in adults, is sensorineural hearing loss. This type of bilateral hearing loss can result from any one of a number of causes, including:

Noise-Induced Hearing Loss
This can occur due to prolonged and ongoing exposure to noise, such as machinery or loud music, or after a single exposure to a loud sound. Sometimes, noise-induced hearing loss is temporary, but with enough exposure to loud noise, it will become permanent.

Age-Related Changes and Hearing
This type of hearing loss is called presbycusis. Over time, the inner ear structures and nerve pathways can be damaged by use. This is the most common cause of hearing loss in older adults. 

Exposure to Ototoxic Drugs
Ototoxic drugs can damage the inner ear. Drugs include aminoglycosides such as gentamicin, chemotherapy agents such as cisplatin, high doses of aspirin or loop diuretics.

Infections
Including viral infections such as measles and mumps and bacterial infections such as untreated middle ear infections.

Autoimmune Disorders
Autoimmune ear disease causes the immune system to attack and damage the inner ear structures. This hearing loss can fluctuate or progress over time. These hearing losses can occur quite suddenly.

Genetic Conditions
Genetic factors such as gene mutations that cause hearing loss, such as a connexin 26 mutation, or cause hearing loss as part of a broader syndrome such as Usher syndrome or Waardenberg syndrome.

Prenatal Factors
Exposure to certain infections during pregnancy, such as cytomegalovirus (CMV) and rubella, can cause bilateral hearing loss. Some infections cause hearing loss at birth, while others cause it to develop or progress over a person’s lifetime.