Otosclerosis: symptoms and causes

What is otosclerosis?
Otosclerosis of the ear (also called osteodystrophy of the labyrinth capsule) is a condition that affects the cochlea and stirrup, namely one of the three ossicles of the middle ear.

In normal hearing, the ossicles of the middle ear (anvil, hammer and stirrup) vibrate freely in response to the sound waves.

In otosclerosis, an abnormal bone stitch grows around the stirrup. As a rule, the stirrup foot plate is affected, which:

  • is in contact with the aurilia;
  • transmits sound vibrations from the eardrum.

This pathologically excessive bone material reduces the mobility of the stirrup. As a result, the amount of sound transmitted to the cochlea – the organ that converts the mechanical sound vibrations into nerve impulses – decreases.
Over time, this bone deposition hinders the mobility of the stirrup, which fuses with the bone of the cochlea, resulting in severe hearing loss.
In this case, hearing loss is defined as conductive hearing loss. This means that the sound vibrations cannot be transmitted from the stirrup to the cochlea.

In most cases of otosclerosis, only the stirrup is affected. Over time, otosclerosis also affects:

  • on the bone coating of the cochlea,
  • on the nerve cells inside.

When this happens, the transmission of nerve impulses to the brain is at risk: this is sensorineural hearing loss.

As a rule, both ears are affected by otosclerosis (bilateral), but only one ear may be involved (monolateral).
The age at which this disorder occurs is about 15 to 30 years. Only rarely does it affect children.

Types of hearing loss

The outer ear and middle ear transmit the sound vibrations, while the inner ear receives them.

  • If there is a malfunction in the middle or outer ear, the sound signal transmission (transmissible hearing loss) is impaired.
  • If the disorder occurs in the inner ear, the result is sensorineural hearing loss.
  • If the disorder affects both the transmission and neurosensory components, the hearing loss is a “mixed” or combined one: the mixed hearing impairments are common in otosclerosis.


Types of otosclerosis

Cochlear otosclerosis
If otosclerosis affects the inner ear, it causes sensorineural hearing loss because it impairs the functioning of the cochlea.
This type of otosclerosis is permanent and can also spread to the semicircular ducts (of balance), as well as cause episodes of instability.

Otosclerosis of the stirrup
Otosclerosis usually spreads to the stirrup, the last link in the chain of transmission of the formwork line in the middle ear. The stirrup rests on a small gap, the oval window, which is in direct contact with the inner ear fluids. Anything that interferes with the function of the stirrup leads to the inability to correctly transmit the sound waves to the inner ear. This type of damage is called stapesankylosis and can be corrected by surgery.

Development of otosclerosis (patophysology)

Usually, hearing loss begins between the ages of 10 and 30 and at this stage it is called otospongiosis.

During this time, an active reconstruction of the ear bones takes place.

Researchers do not yet know with clarity how otosclerosis develops. Nevertheless, there are different hypotheses.

At this stage:

  1. there is no hearing loss in the transmission structures of the middle ear,
  2. sensory hearing loss may occur.

The hearing loss (hypoacusis) can be caused for the following reasons:

  • Migration of lysosomal enzymes (trypsin, stromelysine, phosphatase from bone to inner ear).
  • Spiral band atrophy due to changes in the lamellar bone in the inner surface of the cochlear capsule.
  • The degeneration of the stria vascularis, which does not allow blood flow appropriate to the capsule structures of the ear. In the initial stages, fluoride treatment may be useful.

The sensory component of the condition can lead to complete deafness, but fortunately, this rarely happens.

Dizziness occurs in 15% of cases due to degeneration of the vestibular ganglion (scarpa ganglion).

The cause of dizziness is unknown, hypotheses are:

  • release of enzymes from bones in the middle ear,
  • Blockage of fluid circulation due to bone growth.

Causes of otosclerosis

The causes of this condition are unknown, but researchers have identified some risk factors for otosclerosis, including:

  • Family determination – There is a genetic or hereditary component associated with this disorder.
  • Gender – Women are more likely than men to develop this condition.
  • Pregnancy – Some women develop otosclerosis during pregnancy.
  • Ethnic origin – Caucasians are most affected.
  • Osteogenesis imperfecta – This genetic condition is characterized by abnormally brittle bones: people affected by this disease have a greater risk of developing otosclerosis.
  • Water without fluorine – Some research shows that drinking water that does not contain fluorine increases the risk of developing otosclerosis in predisposed people.
  • Measles virus – There is scientific evidence that the measles virus is involved in the development of otosclerosis. (Arnold W, Busch R, Arnold A, Ritscher B, Neiss A, Niedermeyer HP. 2007. The influence of measles vaccination on the incidence of otosclerosis in Germany. Eur Arch Otorhinolaryngol 264: 741-8)
  • There is insufficient scientific evidence linking otosclerosis to an autoimmune disease (Karosi et al 2009)
  • Unknown causes – Some people develop otosclerosis without certain risk factors.

Symptoms of otosclerosis

In an otosclerosis patient, the doctor first focuses attention on one ear, although both ears are affected by the disease. Here are the main symptoms:

  • Gradual and progressive hearing loss, not complete deafness. The course is very slow, except for juvenile otosclerosis, which is characterized by rapid deterioration.
  • Hearing improves in noisy environments.
  • Tinnitus or ringing in the ears (ringing in the ear). (Sparano A, Leonetti JP, Marzo S, Kim H. 2004. Effects of stapedectomy on tinnitus in patients with otosclerosis. The international tinnitus journal 10: 73-7)
  • Dizziness or vertigo.
  • Disturbances of equilibrium.
  • Nystagmus.
  • Speaking softly (due to a stronger perception of the sound of the voice).

Diagnosis of otosclerosis

The competent specialist is the otolaryngologist who examines the patient and prescribes some examinations, including:

  • Audiometry – to measure the threshold of hearing; usually a person with otosclerosis has hearing problems with low-frequency sounds.
    The stapedius reflex (contraction of the stirrup muscle designed to reduce the transmission of too intense sounds to the snail) disappears in severe otosclerosis.
  • Tympanometry – is an examination method for measuring the mobility of the tympanic membrane, which is subjected to pressure fluctuations.
    The data are displayed graphically in a diagram (tympanogram), the course form shows the disorder in the patient.
    In otosclerosis, tympanometry shows stiffness of the bone chain (hammer, anvil and stirrup).
  • Tympanogram – it can indicate a Carhart depression, which prevents a deterioration of bone conduction at 20-30 dB, especially at 2000 Hz.
  • CT – is used to detect possible damage to the labyrinth and excludes:
    • Brittle bone disease
    • Paget’s disease.

Stages of otosclerosis:

  • Stage I: conductive hearing loss, amplified at low frequencies measurable.
  • Stage II: mixed hearing loss, mainly transmissive, hearing loss at high and medium frequencies (less severe).
  • Stage III: mixed hearing loss, mainly neuro-sensory, otosclerosis worsens and degeneration of the inner ear becomes more severe.
  • Stage IV: neurosensory damage is severe and prevalent compared to the transmission component.

Complications and consequences of otosclerosis

Otosclerosis rarely affects the inner ear and cochlea, the most important organ for hearing. This condition damages the tiny hair cells in the cochlea, which convert the sound waves into electrical signals, which increases hearing loss.
This hearing loss is known as sensorineural hearing loss and is not treated surgically.

If otosclerosis spreads to the area of the inner ear responsible for balance, it can cause dizziness.

Otosclerosis and pregnancy
The female hormones accelerate the progression of otosclerosis. This means that in a pregnant woman, otosclerosis quickly worsens, but this also happens with:

People with otosclerosis should talk to their doctor before starting hormonal treatment.

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