Hearing Loss Overview, Part 2
Sensorineural Hearing Loss

by Barry Keate

Editor's Note: This is the second article of a two part series on hearing loss. Last month Barry Keate provided a discussion on hearing loss in general and conductive hearing loss specifically. In the interest of continuity we have reprinted his initial overview on hearing loss. The second part of this article deals specifically with Sensorineural Hearing Loss (SNHL) and its relationship to tinnitus.

Author’s Note: Much of the information for this article was garnered from the American Academy of Otolaryngology-Head and Neck Surgery Foundation (AAO-HNSF), especially the book “Primary Care Otolaryngology” by Gregory Staffel, MD, who donated the book to the AAO-HNSF. Other material came from the Mayo Clinic and the American Speech-Language-Hearing Association. We are indebted to these organizations for their contributions.

Tinnitus is most frequently the result of hearing loss and most people who experience hearing loss will have tinnitus as one of the symptoms. While exact numbers are difficult to determine, the American Tinnitus Association estimates that 70% of tinnitus is due to hearing loss. This overview will discuss the various types of hearing loss, the causes and available treatments, when applicable.

Hearing Loss

The ear consists of three major areas: the outer ear, middle ear and inner ear. In normal hearing, sound vibrations are funneled by the outer ear into the ear canal where they cause vibrations in the eardrum. These vibrations transfer to the three small bones of the middle ear, the malleus (hammer), incus (anvil), and stapes (stirrup), which amplify the vibrations as they travel to the inner ear. There, the vibrations pass through fluid in the cochlea, a snail-shaped structure in the inner ear. Attached to nerve cells in the cochlea are thousands of tiny hairs that help translate sound vibrations into electrical signals that are transmitted to the brain. The vibrations of different sounds affect these tiny hairs in different ways causing the nerve cells to send different signals to the brain so it can distinguish one sound from another.

There are two basic types of hearing loss: conductive hearing loss, and sensorineural hearing loss. Sometimes there are elements of both and it is termed mixed hearing loss. Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the small bones of the middle ear. The most prevalent causes of conductive hearing loss are: fluid in the middle ear from colds, allergies, eustachian tube dysfunction, ear infection; otosclerosis; perforated eardrum; and impacted earwax.

Sensorineural hearing loss occurs when there is damage to the inner ear, or cochlea, or to the nerve pathways from the inner ear to the brain. This accounts for the majority of hearing loss. Sensorineural hearing loss is considered by the medical establishment to be permanent because there is no medically recognized treatment or surgery that will cure the condition.

The most prevalent causes of sensorineural hearing loss are: disease; drugs that are toxic to the auditory system (ototoxic); noise exposure; viruses; head trauma; aging; and tumors.

During the research for this article I was intrigued to discover how the various tests for hearing loss, audiograms and tympanograms, can narrow down the type of hearing loss and provide very precise information on exactly what problems may have developed and how well the ears are functioning. Pure tone audiometry is used to assess the patient’s hearing levels. During the audiogram, independent hearing thresholds are determined for both air conduction and bone conduction. Air conduction is when the sound travels through the air into the ear and the cochlea. This measures the ability of the ear to conduct sound. Bone conduction bypasses the middle and outer ear by sending sound waves through the mastoid bone directly to the cochlea. This tests for sensorineural hearing loss.

Tympanograms test for mobility of the ear drum which can determine whether there is high or low pressure in the middle ear, caused by fluid build-up or negative pressure due to poor eustachian tube function.

Speech discrimination testing is also conducted by presenting phonetically similar sounds into the audiogram. This test of clarity also reveals the function of the auditory, or 8th cranial, nerve. Amplifying garbled speech with a hearing aid has very little benefit for someone with poor speech discrimination.

Hearing threshold levels are determined between 250 and 8000 hertz (Hz) and measured in decibels (dB). Human speech ranges from 300 to 4,000 Hz. The 0 dB level is normalized to the minimum hearing level of young healthy adults and does not mean there is an absence of sound. The sound level is increased at each frequency until it is heard by the patient. The higher the threshold level, the poorer the patient’s hearing. Thresholds higher than 25 dB are considered abnormal.

Sensorineural Hearing Loss

There are many contributing factors to sensorineural hearing loss. Most of these are considered untreatable by the traditional medical establishment because there are no medically recognized therapies or surgeries that will cure the condition.

Despite that opinion, there are many treatment options that, while not a cure, will result in a lessening of the tinnitus associated with hearing loss. These treatments range from diet and exercise, to supplements, sound therapy and some prescription medications. Most of these treatment options can be seen in our Tinnitus Library .

Disease Conditions
Disease conditions such as Meniere’s disease can lead to sensorineural hearing loss and tinnitus. Little is known about the underlying cause of Meniere’s disease however there are treatments for it. It involves a fluid build-up in the vestibular system that will eventually damage the hair cells of the cochlea leading to permanent hearing loss and tinnitus. A complete discussion of Meniere’s disease can be seen in our Tinnitus Library.

Thyroid disease
Thyroid disease usually causes hearing impairment and tinnitus. The condition results in a decrease in thyroid hormones that can also cause Fibromyalgia and Chronic Fatigue Syndrome. This condition is commonly treated with prescription thyroid hormones. A full discussion on thyroidism can be seen in our Tinnitus Library.

Ototoxic Drugs
There are over 200 prescription and over-the-counter medications that can cause or worsen hearing loss. We have heard from countless people who complained of hearing loss and tinnitus after taking a new medication. Anyone who already has hearing loss should exercise caution when taking new prescription medications. Make certain your physician knows about your hearing condition and concerns. An article on ototoxic medications can be seen in our Tinnitus Library .

Noise Exposure
This is a very common cause of hearing loss and tinnitus and is the cause of my hearing loss, as mentioned in the previous article. Noise exposure permanently damages the hair cells in the cochlea. It is common in certain industries and is closely regulated by the Occupational Health and Safety Administration (OSHA).

The following graph compares the loudness of common sounds.

Below are the maximum noise levels on the job to which you should be exposed without hearing protection and for how long. Most experts agree that continual unprotected exposure to more than 85 decibels is dangerous and leads to hearing loss.

Presbycusis
Commonly referred to as age-related hearing loss, Presbycusis is by far the most frequent cause of hearing loss in the elderly. As we age, the outer hair cells in the cochlea gradually deteriorate causing bi-lateral hearing loss, primarily in the higher frequencies. Patients with presbycusis may also have difficulty with speech discrimination and complain of tinnitus.

One of the most widely investigated potential causes of presbycusis concerns reduced blood flow in the cochlea associated with age that contributes to the formation of oxygenated free radicals. These molecules damage the mitochondrial DNA that leads to problems with neural functioning in the inner ear.

Presbycusis can be prevented but once it occurs it joins the stable of other causes of sensorineural hearing loss and becomes permanent. Michael Seidman, MD has done pioneering work in this area and has obtained a US patent for a product that prevents mitochondrial damage to the inner ear. The product is called the Anti-Age/Energy Formula.

Dr. Seidman has also written a book called “Save Your Hearing Now" that details the progressive damage done to the inner ear by free radicals and outlines a complete plan for preventing damage and prolonging acute hearing ability.

Tumors
The primary tumor associated with hearing loss is an acoustic neuroma. This is a very rare, slow-growing, non-malignant tumor that occurs on the 8th cranial nerve controlling hearing and balance. In many cases these are left alone, especially if the patient is elderly and the tumor small. In other cases they must be surgically removed. If left to grow too large they will eventually impact on the brain and can be life threatening. Read a complete discussion on acoustic neuroma in our Tinnitus LIbrary.

Head Trauma
Numerous reports in the literature indicate that head trauma, which includes concussion and whiplash, causes hearing loss and tinnitus. Damage can occur to the bones of the middle ear or the 8th cranial nerve. The hearing loss may be temporary or permanent, depending on the degree of damage. The hearing loss mimics the hearing loss due to noise exposure, with a typical downward notch at 4 KHz.

Arches Tinnitus Formulas were developed to help people suffering from tinnitus due to sensorineural hearing loss, regardless of the cause. While not a cure, the formulas have helped thousands of people reduce the sound level and continue with an enjoyable life. Read a highly informative article on the Science Behind the Product .