Conductive vs. Sensorineural Hearing Loss
Otological pathology is the process of evaluating and treating abnormalities and damage that occurs with hearing. In assessing the patient, the patient medical history, age, and genetic or hereditary factors are crucial for a proper evaluation to determine the hearing loss and the extent of the damage.
Hearing loss can be transitory or permanent, depending on the nerve pathway's damage that travels from the inner ear to the brain. When impairment is transitory or temporary, there are more straightforward remedies than if irreparable harm occurs, which often requires hearing aids and possible surgical treatments.
Types of Hearing Loss
There are three main types of hearing loss. These types of hearing loss are Conductive, Sensorineural (SNHL), and Mixed Hearing Loss.
Conductive Hearing Loss is usually correctable, while Sensorineural Hearing Loss can frequently become a permanent condition. With Mixed Hearing Loss, the damage is from both Conductive and SNHL, and any treatment should address both forms of hearing loss and corrective procedures.
Conductive Hearing Loss is a condition that occurs when there is an issue with sound reaching the inner ear, usually from a form of blockage in the outer or middle ear.
Sensorineural Hearing Loss occurs when there is damage in the inner ear that affects how sound is absorbed by the auditory nerve and cochlea, making sound delivery to the brain difficult. The cochlea is the main organ associated with hearing, and damage to the cochlea is typically permanent.
The main difference between Conductive vs. Sensorineural Hearing Loss is where the damage occurs and the available types of corrective procedures. Another key difference is that Conductive Hearing Loss is more often treatable than SNSL hearing loss that results from damage to the ability to hear, and is more permanent.
The Ear Construction And Evaluation
The ear consists of three sections, the outer ear, middle, and inner ear. Additionally, the auditory pathway makes the final phase of the hearing. Any ear examination’s primary scope will look at these three physical sections and the auditory way, including the tympanic membrane and the cochlea.
The outer ear consists of the ear lobe is the visible part, known as the pinna, the ear canal, and the tympanic membrane. The tympanic membrane separates the outer and middle ear.
The middle ear consists of the eardrum and three small bones, known as ossicles, that send movement from the eardrum to the inner ear.
The inner ear is made up of the spiral shaped cochlea, semicircular canals which assist with balance, and nerve endings, such as the auditory nerve, that sends signals to the brain to process
There are four degrees of hearing loss, from mild to profound.
- Mild: Speaking voice is understandable though soft sounds may be difficult
- Moderate: Speech at an average volume is indecipherable at times
- Severe: At a normal volume, speech is impossible to hear; only some loud noises are decipherable
- Profound: Speech is unheard, and only extremely loud sounds can be heard
There may be additional causes of hearing loss unassociated with the ear, and a thorough examination will eliminate other causes.
To begin an evaluation of the patient's medical history and family history are essential to establish a baseline understanding.
Typical questions in evaluating a patient experiencing hearing loss are first to address the patient's history. A standard evaluation should include items such as;
- When did you first experience hearing loss?
- Was your hearing loss sudden or gradual?
- Is there pain and discomfort associated with hearing loss?
- Are you experiencing hearing loss in one ear, known as unilateral hearing loss, or in both ears, known as a bilateral hearing loss?
- What is your personal history regarding hearing loss? What is your medical history as related to hearing?
- How about family history, genetic, or hereditary factors with hearing loss?
- Do you have a history of any disease, Diabetes, stroke, or heart conditions?
- What is your work environment? Are you around sudden or continuously loud noise?
- Are you currently on any medications?
- Have you received any diuretics, antibiotics, or chemotherapy before experiencing hearing loss?
Once the baseline evaluation is concluded, a physical exam of the ear will determine the level of damage and possible remedies.
The physical examination will include a visual inspection of the outer and middle ear canal to observe the ear canal's color and abnormalities. By using an Otoscope, your Primary Care Physician or ENT will be able to determine if there are any issues with the tympanic membrane and whether there is any aeration or abnormal air-flow within the inner ear.
Determining Conductive Vs. Sensorineural Hearing Loss
One of the next tests performed, known as Weber's test, is when a tuning fork is placed on the forehead, teeth, or midline of the scalp to evaluate what frequencies may be heard and any muffled or obstruction affecting hearing.
If the hearing loss is due to Conductive Hearing Loss, the sounds are heard best in the affected ear. If the issue is Sensorineural Hearing Loss, the sounds will be heard better in the unaffected ear than in the damaged ear. The sounds will be midline between both ears for patients experiencing Mixed Hearing Loss or little-to-no hearing issues.
The next test in the evaluation, known as the Rinne test, places the tuning fork on the mastoid bone, located just behind the inner ear. The tuning fork is moved toward the ear canal to register where the hearing loss is located and where the abnormal or less affected hearing loss occurs. This location test determines whether there may be a physical blockage in the ear canal or if the issue is more with the auditory pathway.
With hearing located at the mastoid bone, this is known as bone conductive hearing, while situated in the ear canal is known as air conduction. With normal hearing and sensorineural hearing loss, air conductive is better than bone conduction, and sound from the tuning fork can still be heard at the ear canal. With Conductive Hearing Loss, bone conductive is better than air conductive, and the sound of the tuning fork is lost or muted near the ear canal.
Additionally, testing softer frequencies is crucial. Quieter frequencies are often muffled with Sensorineural Hearing Loss than Conductive, so whispering or using a sound generated at a lighter volume frequency is essential to determine the hearing range to best assess the type of hearing damage.
For more in-depth examination, speech testing is used to determine the range of speech pathology and should be done in conjunction with an audiometry test to test the range of sounds, pitches, and frequencies. A quick head and neck examination should follow.
Conductive Hearing Loss
Conductive Hearing Loss stems from some cause that is typically from a fluid or physical blockage in the outer-to-middle ear. The reason can often be from trapped fluid in the ear canal, disease or infection, physical trauma, or even genetic defects.
Often referred to as temporary (or transient) hearing loss, Conductive Hearing Loss is caused by some form of blockage, whether from tissue, bone, or fluid. There could be an object in the ear canal; a misformed ear canal; or some other form of blockage that may have occurred. It can typically be treated with your Primary Care Physician, and if not, then a diagnosis and treatment are referred to a specialist known as an Ear, Nose, Throat (ENT) specialist.
Often with Conductive Hearing Loss, the treatment is handled with simple procedures, antibiotics, though in difficult situations, may require surgery. Again, an ENT or your physician can determine the specific type of hearing issue.
During treatment, if more severe hearing loss and damage may have occurred, the prognosis (a Baha) may require the use of hearing aids or a surgically anchored device that attaches to the bone in the ear.
Knowing the symptoms of Conductive Hearing Loss will allow the evaluator to assess the types of remedies available quickly. A simple physical exam will help exclude many other possibilities, but the diagnosis must consider other more severe causes.
Symptoms of Conductive Hearing Loss
Symptoms of Conductive Hearing Loss maybe, but not limited to:
- Muffled sounds and hearing, incredibly loud sound and specific frequencies
- A feeling of stuffy, fullness in the ear
- Pain and discomfort in the ear
- Dizziness and vertigo
- An odor, especially foul-smelling coming from the ear
- Fluid draining from the ear
These symptoms are clues that the ear canal has a blockage and can't effectively allow sound to travel through the ear canal. Children will often complain about pain and discomfort or tug and rub the infected ear to illustrate what is hard to communicate. As with any discomfort or pain associated with your ears, you should see your primary care physician for an evaluation.
Causes of Conductive Hearing Loss
With Conductive Hearing Loss, most treatments are through minor procedures and antibiotics and antifungal medications. These are often temporary hearing loss types that don't require too much attention to correct the issue.
Some of the most common causes of Conductive Hearing Loss can be attributable to the following:
- A malformed ear canal or other ear structure
- Otosclerosis - a genetic disorder that affects the small bone in the middle ear, limiting its vibration when stimulated by sound
- Impaired Eustachian tube function
- Foreign objects
- Tumors in or around the ear
- Ear wax - common causes of blockage are from cotton swabs being inserted too far into the ear canal, pushing the wax deeper into the canal and creating blocking
- Allergies and colds that trap water in the middle ear
- Infections in the ear canal or the surrounding area
One or more causes of Conductive Hearing Loss and any combination can lead to discomfort or pain. Typically younger children are more susceptible to Conductive Hearing Loss due to viral and bacterial infections. However, adults who participate in activities with exposure risks associated with surfing or open water diving are prone to illness at a higher rate than the general population.
Another common cause for Conductive Hearing Loss is attributable to in-ear headphones and regular use of earplugs. What happens is that bacteria or viruses contaminate the device's surface and expose the ear canal to the pathogen when applied to the ear. Additionally, overuse of these devices can impact ear wax secretions and cause blockage to occur. To avoid this type of exposure, it's essential to regularly change out earplugs and adhere to the headphone manufacturer’s cleaning procedures.
In more severe Conductive Hearing Loss cases, treatment may require surgery, especially in cases of a genetic disorder, malformation, or head trauma.
Sensorineural Hearing Loss
Sensorineural Hearing Loss, or SNHL, is damage that occurs to the inner ear. It is typically a nerve-related type of hearing impairment and is a more permanent form of hearing loss. With SNHL, the neural pathways in the auditory complex are damaged. The causes of Sensorineural Hearing Loss can be environmental, such as exposure to sudden or prolonged loud noise, disease, aging, and other factors.
With Sensorineural Hearing Loss, the typical treatment is addressed with cochlear implants or traditional hearing aids. However, some forms may require more invasive measures or be coupled with medication to correct the issue.
Causes of Sensorineural Hearing Loss
The most common forms of hearing loss stem from age, exposure to loud noise, and hereditary or genetic makeup. Damage to the inner ear can cause permanent hearing loss.
Some of the most recurring forms of hearing loss are caused by the following:
- Aging (presbycusis): Degenerative hearing loss due to aging occurs for one of every three people over 65
- Noise: Exposure to sudden or prolonged loud noise can permanently damage cells and nerves in the cochlea
- Disease: Bacterial and Viral infections
- Head Trauma or sudden air pressure changes, such as plane descent
- Autoimmune ear disease: a rare condition that affects only 1% of 28 million people
- Otosclerosis: Abnormal bone growth in the middle ear that impacts the hearing ability
- Genetic and Hereditary conditions
Less common forms of Sensorineural Hearing Loss can occur from other underlying health conditions such as diabetes or heart disease and certain types of disease and cancers. Meniere's disease is a rare type of illness that may cause SNHL in adults. Meniere's disease symptoms are; A fluctuating sensorineural hearing loss associated with hearing loss, vertigo, and ringing in the ears, a condition known as Tinnitus.
Tinnitus is a condition that affects upward of 20% of all people, whether suffering permanent or transitory hearing loss. It is a symptom of an underlying condition, not a disease in itself. Symptoms are a constant buzz or ringing in the ear and may come and go and subside in time.
Sudden Sensorineural Hearing Loss
Sudden Sensorineural Hearing Loss is a condition caused by a viral infection and is critically serious. Treatment is with corticosteroids that may help reduce cochlea hair swelling. It is a medical emergency that should be treated immediately.
However, with Sudden Sensorineural Hearing Loss (SSHL), the prognosis is upbeat. The recovery rate of people who suffer from SSHL is as high as 85%, with a third to two-thirds of recovery time occurring within two-weeks time.
More severe types of Sensorineural Hearing Loss may be attributable to Temporal Bone Fracture, a condition where damage occurs to the temporal bone causing unilateral SNHL and Conductive Hearing Loss. This cause may be due to facial nerve paralysis or intracranial injuries resulting in cerebrospinal fluid leakage. If that is the case, it may require immediate medical and surgical remedies.
Symptoms of Sensorineural Hearing Loss
As with Conductive Hearing Loss, soft sounds may be difficult to hear, and loud noises may be muted or unclear. However, clear signs that hearing loss may be more of the SNHL variety versus Conductive Hearing Loss can exhibit the following:
- Speech may be difficult to hear or may appear muted in loud rooms, making it difficult to follow and understand
- The difficulty can differentiate conversation when more than one individual is speaking. Words may be jumbled and unclear.
- Consistent Tinnitus, or ringing in the ears, may occur.
- High-pitched sounds and words, especially from women or children, maybe incomprehensible
- Soft-sounds in words such as "th" or an "s" sound may blur and be unclear.
- A sense of vertigo or lack of balance, dizziness
Diagnosing Sensorineural Hearing Loss
In diagnosing Sensorineural Hearing Loss, a typical hearing examination, as described previously, should take place. Once the condition is determined to be Sensorineural versus Conductive Hearing Loss, one should take an additional follow-up exam to determine the amount of damage that has taken place.
As discussed previously, checking a patient's medical history and comparing that with apparent symptoms will help with the proper diagnosis. Evaluate the patient's history, duration of hearing loss, and the physical examination to evaluate the cause of SNHL best.
For example, in older patients with the normal tympanic membrane but who experience bilateral, gradual hearing loss, the result is most likely due to presbycusis, or aging.
A person who works around loud noises for a prolonged duration or in an environment with sudden loud noise should wear protective equipment to limit the impact on hearing, and the Occupational Safety and Health Administration (OSHA) has specific guidelines in place to protect hearing health.
Other Types of Hearing Loss and Prevention
The most preventable form of hearing loss is noise prevention. Typical exposure to over 4000 Hz, such as from gunfire, explosions, or loud music over a long time, can do irreparable harm to the cochlea's hair, causing severe hearing loss. Members of the armed forces, police units, or others that regularly use firearms and construction workers or manufacturing jobs are at higher risk of complications of loud noise and hearing damage.
One form of hearing loss that is less common in various ototoxins is gentamicin, streptomycin, and other antibiotics. Care must be considered when administering antibiotics or chemotherapeutics with older patients who may also have other underlying health issues. Patients who experience ototoxicity may exhibit vertigo in addition to hearing loss issues. Great care should be given before any prescriptions or medication given, especially those at higher risk of side effects.
In short, a person suffering Conductive vs. Sensorineural Hearing Loss is one who struggles to hear air-conducted sounds as opposed to bone-conducted sounds. With Conductive Hearing Loss, softer sounds will be difficult to hear while louder sounds will be muffled.
People with Sensorineural Hearing Loss can hear air-conducted sounds easier than bone conducted sounds. With SNHL, soft sounds, particular higher frequencies, are muted and difficult to hear, while loud sounds may be muffled as well. SNHL is the most common form of permanent hearing loss as the auditory pathway’s nerve structure is damaged.
Conductive and Sensorineural Hearing Loss may have similar causes, primarily due to viral or bacterial reasons or those associated with the degenerative process attributable to aging.
The main differences between Conductive vs. Sensorineural Hearing Loss stem from the severity of the damage done. With Conductive Hearing Loss, the damage is less severe and allows the sufferer more treatment options available. At the same time, Sensorineural Hearing Loss can be more catastrophic for the sufferer and lead to more permanent hearing loss.
While Conductive Hearing Loss is usually treatable instead of Sensorineural Hearing Loss, both types should be evaluated and addressed by your primary care physician. From medication to hearing aids, implanted assisted hearing aids, and other types of assistive hearing devices, the good news is that there are solutions available even with hearing loss.
Drew Sutton M.D.
Drew Sutton, MD is a board-certified otolaryngologist. He has extensive experience and training in sinus and respiratory diseases, ear and skull base surgery, and pulmonary disorders. He has served as a Clinical Instructor at Grady Hospital Emory University for more than 12 years.