Otosclerosis
Otosclerosis is a disease of the bone, unfortunately its name is misleading it should be named otospongiosis, because the diseased bone is softer than the bone it replaces. It is an instance where the disease was named before the process was fully understood. Otosclerosis is the most common cause of a loss of hearing in early and middle adult life. Yet the cause is unknown but it may have a genetic basis as half of the sufferers’ have a relative with the same problem. It is much more prevalent amongst Caucasians and twice as many men as women suffer from it.
The softened otosclerotic bone first appears in late childhood or in the teenage years, but in the majority of cases it never produces symptoms it is only ever detected after death after a post mortem examination. From this we know that of those that have undergone a post mortem ten percent of the men and twenty percent of the women have this condition in adult life.
In about one in eight of the cases the mass of the softened bone increases until it reaches the stirrup bone and the expanding nodule creates a build up of pressure, and it cannot vibrate when the sound reaches the eardrum. Once this has occurred the sharpness of sound is lost, and then the sufferer cannot hear the low frequencies very well, later they cannot discern whispers, and then conversational sound coming from a distance. It continues to get progressively worse until they can only hear the spoken word if it is being said close to the ear.
We have already discussed air and bone conduction of sound and one of the oddities that do occur when the stirrup becomes fixed is that the person can hear better by bone conduction. That means if they want to hear a telephone conversation if they put the receiver against their head and bypass the ear they can hear by bone conduction.
They also hear better when they are on a train in an airplane or a car, and this is because when people speak when there is a low throb of machinery in the background they do tend to raise their voice. The Otosclerosis sufferer cannot hear the hum of the machinery but they benefit from listening to the raised volume of sound.
Hearing tests carried out using an audiometer demonstrate that the hearing by bone conduction is better than by air conduction. The diagnosis of stirrup fixation by Otosclerosis begins with the history of the hearing loss with the absence of any chronic infection of the middle ear or of perforation of the tympanic membrane providing that the auditory nerve in the inner ear is capable of functioning if only the sound could reach it.
The final and conclusive diagnosis of Otosclerosis is a finding made through surgical exploration which reveals that a nodule of bone has caused the stirrup to be fixed. It can nearly always be corrected by a stapedectomy a small surgical procedure that removes the fixed stapes and replaces it with a non-biological substitute.
Sometimes the otosclerotic bone disease expands as far as the cochlea of the inner ear, and this causes the auditory nerve to deteriorate. This progressive nerve deafness can occur before, during or after the stapes becomes fixed, and in some cases it can occur without the fixation of the stapes bone. However whilst the cause of the disease is unknown it is known that drinking water, which has an additive of fluorine, hardens the softened nodule of otosclerotic bone, and prevents its expansion and also prevents the subsequent chance of the auditory nerve deteriorating.
The Eustachian tube drains the mucus from the middle ear into the throat. When a child has a cold or an allergy the Eustachian tube is blocked by either mucus or congestion. The middle ear is normally filled with air but when the Eustachian tube cannot drain because it is blocked, fluid builds up in the middle ear. The Eustachian tube can also bring with it both bacteria and viruses, these are then trapped in the fluid filled middle ear, where they breed and cause an ear infection.