What Is Asymmetrical Hearing Loss?

Hearing loss is a debilitating condition that can make the most routine things in life very frustrating. Something as simple as having a conversation with a friend can become a challenge and a chore.

But not all experiences with hearing troubles are the same. For many, hearing loss affects one ear more than the other. In asymmetrical hearing loss, the ears have differing hearing abilities. 

This article looks closely at asymmetrical hearing loss, examining some of the causes and possible solutions. 

What Is Hearing Loss?

Contrary to popular belief, hearing loss is not a condition that is only reserved for the older adults among us. 

While it is true that age is the strongest predictor of hearing loss, it is by no means the only cause.

Hearing impairments can affect anyone, from infants to the elderly and anyone in between. 

Loss of hearing remains one of the most common, debilitating conditions worldwide.

According to global hearing loss statistics by the World Health Organization (WHO), hearing loss impacts roughly five percent of the world’s population. This ranges from mild hearing loss to deafness. 

Hearing loss impacts everyone differently.

While some experience the same degree of hearing loss in both ears (bilateral hearing loss), others experience asymmetrical hearing loss. 

What Is Asymmetrical Hearing Loss?

Simply put, asymmetric hearing loss occurs when hearing loss is greater in one ear than in the other.

However, to qualify as a true asymmetric hearing loss, there must be a measurable difference in hearing loss degree between the ears. 

How Is Hearing Loss Measured?

The degree of hearing loss is found by establishing the hearing level — how loud things must be before you hear them — and frequency (pitches).

Sound is measured in units referred to as decibels (dB). Decibels measure sound intensity. 

For example, a normal conversation is typically around 40 to 60 dB. We can tolerate this threshold of sound just fine. 

But, when we experience decibel levels of more than 85 dB for a prolonged period, damage to our hearing can occur. For reference, a lawnmower is around 90 dB. 

Aside from sound intensity, sounds are also measured by frequency or pitch. Frequency uses Hertz (Hz). Men tend to have a lower speech frequency than women. 

Normal speech has a frequency range between 250 Hz to 8000 Hz. But, humans can also detect high frequencies, up to 20 kHz (20,000 Hz).

How Severe Is Asymmetrical Hearing Loss?

Asymmetric hearing loss is defined as a difference of 15 dB between the left and right ears.

This must be established at three adjacent frequencies. 

This makes asymmetrical hearing loss unique compared to other configurations of hearing loss. Asymmetrical hearing loss must be bilateral (hearing loss in both ears). 

The difference lies in the hearing loss severity between the two ears. Asymmetrical hearing loss is not the same as unilateral hearing loss — e.g., only hearing loss in one ear. 

What Are the Types of Hearing Loss?

Medically, asymmetric hearing loss can fall into two main categories: conductive or sensorineural hearing loss. Mixed hearing loss is a third category that is simply a combination of the other two. 

Conductive hearing loss occurs when sound cannot pass through the outer ear, ear canal, and middle ear. The main causes of this are obstruction, trauma, and infection. 

Asymmetrical sensorineural hearing loss is far more common. 

Asymmetrical Sensorineural Hearing Loss

Sensorineural hearing loss (SNHL) involves damage to the auditory system, namely the inner ear and auditory nerve. It occurs when these auditory components are damaged or degenerate. 

The inner ear houses important components like the cochlea and receptor cells called hair cells. Along with the auditory nerve, the inner ear helps convert sound waves into electrical signals that travel to the brain. 

Clinically, asymmetrical sensorineural hearing loss is defined in two ways:

  • 15 dB or more difference between the two ears at one frequency, 0.25 to 8 kHz).
  • A difference in bone conduction thresholds of more than 10 dB at two contiguous frequencies. 

Causes of Asymmetrical Sensorineural Hearing Loss

The main causes of asymmetrical sensorineural hearing loss are the same as general sensorineural hearing loss. It typically occurs due to aging (age-related hearing loss) and exposure to loud noise.

Presbycusis, or age-related hearing loss, is one of the most common causes of asymmetrical sensorineural hearing loss. 

Over time, the sensory hair cells and auditory nerve degenerate, leading to hearing loss.

This is most common among older adults, affecting around one in three adults ages 65 to 74. 

According to the American Academy of Otolaryngology, around 40 million American adults aged 20 to 69 have noise-induced hearing loss. This can result in degenerative hearing loss over time or sudden hearing loss. 

Behind aging, long-term exposure to loud noises is the main cause of asymmetrical sensorineural hearing loss.

Other causes of asymmetrical sensorineural hearing loss

While age and exposure to loud noise represent the main causes of asymmetrical sensorineural hearing loss, there are plenty of other culprits. 

The conditions below have a stronger incidence of developing asymmetrical sensorineural hearing loss:

  • Idiopathic sudden asymmetrical sensorineural hearing loss.
  • Infections, like meningitis, mumps, and rubella.
  • Neurological issues, such as multiple sclerosis (MS), stroke, or migraines. 
  • Disease and illness, like Ménière’s disease or autoimmune inner ear disease.
  • CPA (cerebellopontine angle) tumors or vestibular schwannomas (acoustic neuroma).
  • Ototoxic medications, such as loop diuretics, chemotherapy drugs, and more.
  • Acoustic trauma, head injury, or ear/cranial surgery.
  • Retrocochlear lesions or small tumors.

Signs of asymmetrical sensorineural hearing loss

The symptoms of asymmetrical sensorineural hearing loss are not unlike the symptoms of other types of hearing loss.

These include difficulty hearing speech in noisy environments, trouble discerning the direction of sounds, and more. 

One unique symptom of asymmetric hearing loss is unilateral tinnitus, which involves ringing in one ear.

How Do I Identify Asymmetric Hearing Loss?

Hearing loss should always be diagnosed by an audiology professional. This could include an audiologist or ENT doctor (ear, nose, throat). 

These professionals can run audiometric tests, like pure tone hearing tests, and be able to interpret audiograms. 

In addition to audiometry tests, a clinical examination will also be required. This includes examining the skin, external auditory canals, tympanic membranes, head, neck, and cranial nerves. 

Asymmetric hearing loss generally requires further evaluation. This could include auditory brainstem response (ABR) testing or magnetic resonance imaging (MRI). 

An MRI scan is able to examine important components using gadolinium contrasts, like the internal auditory canal. 

How Is Asymmetric Hearing Loss Treated?

Asymmetric hearing loss involves standard hearing loss treatments. This includes amplification devices like hearing aids and cochlear implants. 

Asymmetric hearing loss typically requires two hearing aids for contralateral signaling, also known as “contralateral routing of signals” (CROS). 

Essentially the sound detected by the”bad ear” gets transmitted directly to the aid of the “good ear” to balance things out. 

The Bottom Line

Asymmetrical hearing loss is defined by hearing loss in both ears, with one ear being measurably worse than the other. The causes and general symptoms are not unlike other forms of hearing loss. 

If you suspect asymmetric hearing loss, it’s best to consult an audiology professional who can diagnose the type of hearing loss and follow up with the best treatment options. 

Check out the USA Rx Hearing Loss Blog for more information like this.

References, Studies and Sources:

Deafness and hearing loss | WHO

The Audible Spectrum | Neuroscience

Asymmetrical hearing loss | AFP

Block Out the Noise | AA of Otolaryngol Head-Neck Surg | (AAO-HNS)

Medicolegal concerns among neurotologists in ordering MRIs for idiopathic sensorineural hearing loss and asymmetric sensorineural hearing loss | Otol Neurotol | NIH

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