March 27, 2015

Deafness – Part 1

This is a topic that has many opinions and they are almost evenly divided into the opposing sides. There are those that do not believe diabetes causes hearing loss and those that can offer convincing evidence that it does cause hearing loss. They do agree that there are different types of hearing loss and can have different effects on how sounds are heard and understood. The different types of hearing loss tend to have different causes, and it appears that having diabetes can contribute to the development of certain types of hearing loss. Damage can occur anyplace along the hearing pathway. The location of the damage is the determining factor that determines the type of hearing loss.

The different types of hearing loss are:
Conductive hearing loss (outer and middle ear). Trauma to the structures of the ear that physically transmit sound, such as the eardrum and the bones in the middle ear, can result in conductive hearing loss, which reduces the ear’s ability to physically conduct sound vibrations. The eardrum can be damaged by chronic infection, trauma resulting from pressure changes in the ear (such as those that occur in deep-sea diving), or blunt force to the ear or head. The tiny bones in the middle ear also can be damaged by blunt force. A condition called otosclerosis, which involves abnormal growth of bone in the middle ear, can reduce the strength of the sound vibrations that are transmitted into the cochlea, thereby reducing the volume at which sounds are heard.

Conductive hearing loss causes a reduction in the overall volume of sounds, but if speech can be made loud enough, by means of a hearing aid or the speaker talking louder, for instance, it can most often be understood. In many cases, areas of the ear involved in conductive hearing loss may be treated with medicines or repaired with surgery.

Sensorineural hearing loss and central processing disorders (inner ear and central hearing pathway). Damage to the inner ear or to structures along the nerve pathway is called sensorineural hearing loss because it involves either the delicate sensory hair cells in the cochlea or the hearing nerve, and sometimes both. When the nerve pathway from the ear to the brain is damaged, this is usually referred to as a central processing disorder. Unlike people with conductive hearing loss, those with sensorineural hearing loss or processing disorders may have difficulty understanding speech even when it is amplified. In fact, too high a volume can result in distortion of the speech, causing an unpleasant sound and making it even more difficult to understand.

A person whose sensorineural hearing loss is caused by damage to the hair cells in the cochlea typically has difficulty hearing sounds at particular frequencies, or pitches. This is because each group of hair cells is sensitive only to one frequency, and when any damage occurs, some hair cells may be affected more than others. The hair cells nearest the entrance from the middle ear, which detect high-frequency sounds, seem to be more susceptible to damage related to aging and noise. This can lead to hearing loss in the high-frequency range, making it difficult to understand speech, which contains a mix of low- and high-frequency sounds.

Sudden sensorineural hearing loss. Sensorineural hearing loss that appears suddenly can have a number of causes, including a blow to the side of the head or a sudden loud sound like an explosion. This type of hearing loss can involve a wide range of frequencies, depending on the nature of the injury. Sudden sensorineural hearing loss that has no known explanation occurs only rarely, and in a large percentage of these incidents, the people recover their hearing spontaneously. (Many physicians think these cases are the result of viral infections, but this explanation has not been confirmed.)

There have been reports of sudden sensorineural hearing loss associated with diabetes, but this is extremely rare. However, there is evidence that high blood pressure may increase damage to the small blood vessels in the cochlea of people with diabetes, which could result in sudden sensorineural hearing loss. A recent study found that people with diabetes and sudden sensorineural hearing loss were more likely to have higher blood pressure, higher cholesterol, and a higher HbA1c (an indicator of blood glucose control over the previous 2–3 months) than people with diabetes but no sudden hearing loss.

If you experience sudden hearing loss, you should report it to a physician, preferably an otolaryngologist (ear, nose, and throat (ENT) specialist). It is important to get medical attention as soon as possible, because specific medicines can often recover some or most of the hearing if they are administered early.

Concluded in next blog.

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