Otosclerosis and Otospongiosis – Inner Ear bone disease

Dr. K. R. Meghanadh

What Is Otosclerosis?

Otosclerosis & Otospongiosis are two distinct stages of a hereditary disease that are more common in women.

This condition affects the bones in the ear. The condition primarily affects the otic capsule bone in the inner ear, which is the strongest bone in the human body.

It is a condition marked by the replacement of normal, hard bone with spongy bone. This is often a hereditary disease that progresses through two distinct stages: otospongiosis and otosclerosis.

This condition causes symptoms such as hearing impairment, tinnitus, and dizziness in both stages.

Otospongiosis: The Initial Stagee

Otospongiosis is characterized by the transformation of hard bone into spongy bone, resulting in the swelling of the affected bone, much like a sponge, due to decreased density.

Otosclerosis: The Advanced Stage

As otospongiosis progresses over months or years, the spongy bone is eventually replaced by sclerotic bone, which is thicker and denser. This advanced stage is termed otosclerosis.

Causes

Not all causes of otosclerosis are fully understood, but there are several theories about its causes.

1. Hereditary Factors: There is a significant genetic component associated with otosclerosis. Individuals with a family history of the condition are more likely to develop it themselves.

2. Post-Measles Infection: Some theory proposes that otosclerosis is caused post measles infection. However, no definitive proof establishes measles as a direct cause of otosclerosis.

3. Pregnancy: Otosclerosis is known to be associated with pregnancy, and it tends to occur more frequently in women, especially during or after pregnancy.

4. Age and Gender Factors: While it is more commonly associated with women, otosclerosis can affect both men and women. It usually tends to start around 20 years of age.

Symptoms

The disease initially starts as otospongiosis and then progresses into otosclerosis. The symptoms are the same in both otospongiosis and otosclerosis. These symptoms include:

1. Deafness

2. Tinnitus

3. Dizziness

While symptoms can’t determine whether the disease is in the otospongiosis or otosclerosis stage. Tinnitus and Dizziness are more prominent in Otospongiosis.

How does it Progress?

Otospongiosis condition is characterized by abnormal bone swelling in the otic capsule, the bony covering of the inner ear.

This primarily affects two essential inner ear components: the labyrinth, responsible for balance, and the cochlea, the organ responsible for hearing.

The progression of Otospongiosis to Otosclerosis involves the development of abnormal foci or spots of sclerosis within the otic capsule.

Two primary types of issues arise during the development of otosclerosis. The first scenario occurs when abnormal bone growth occurs in a non-critical area, which leads to minimal consequences. However, when these foci emerge around the stapes bone, consequences arise leading to diminished hearing.

Effect on Stapes Bone – Conductive Hearing Loss

Sound is mechanically transmitted from the eardrum or tympanic membrane to the inner ear by three bones that are connected like a chain. These 3 bones are malleus, incus, and stapes. The malleus is connected to the eardrum while stapes to the inner ear’s cochlea. Stapes bone moves like a piston to transfer these mechanical sound waves to the cochlea, which transforms these signals into electrical signals that could be sent to the brain. Any issue in the process of transferring these mechanical signals to the cochlea causes conductive hearing loss.

So, any disturbance in the stapes movement can result in conductive deafness. This disturbance can be due to Otosclerosis and Otospongiosis.

Effect on Nerves – Sensory Neural Deafness

Another critical area where Otosclerosis and Otospongiosis can significantly impact the multiple blood and nerve canals, specifically the bony canals that house the cochlea nerve fibres. The nerve canal is vital as it facilitates the passage of nerve fibres that are responsible for hearing.

When otosclerosis affects this canal, it can lead to compression of the nerve, blood vessels, or both. This compression disrupts the normal blood supply to the nerve, resulting in the weakening of the nerve and deafness. This type of deafness is called sensory neural deafness.

In some cases, otosclerosis may manifest in both the stapes bone and the nerve canal, resulting in a mixed type of deafness.

Risk Factors – Who is vulnerable?

1. Otosclerosis is a hereditary disease. If a family member is diagnosed with otosclerosis, other family members should be vigilant.

2. Otosclerosis often initiates in and around pregnancy or after delivery.

3. The prevalence of otosclerosis is higher in women compared to men, with approximately 60-70% of diagnosed patients being women.

4. This condition can arise in individuals aged between 20 and 30, affecting both men and women.

Understanding these risk factors is essential for the early detection and proactive management of otosclerosis.

Diagnosis

There are a series of tests that will be conducted upon the revelation of the symptoms. Giddiness or Vertigo, tinnitus and deafness are typical symptoms of an inner ear disease.

Otoscopy

Otoscopy or a visual examination of the ear reveals a normal eardrum, a healthy middle ear.

As mentioned earlier, symptoms often indicate Otitis Interna, an inner ear disease, or an infection in the inner ear, commonly secondary to a middle ear infection known as Otitis Media. A healthy middle ear and a clear eardrum, observed through otoscopy, should raise suspicions in the mind of an ENT expert. This could suggest conditions like Otosclerosis or middle ear bone defects, whether caused by a fracture or a birth defect.

CT scan or Radiology

In most cases, a CT scan indicates the absence of disease in the ear or eardrum. Not in all cases the abnormalities of this disease are shown in the CT scan.

Only a few cases of Otosclerosis and Otospongiosis can be diagnosed with a CT scan. The revelation happens only when there is the thickening of the Stapes bone foot plate or focus of rarefication of the inner ear bone.

Otosclerosis patient ct scan showing hypotension shadow in the area called fistula antefenestrum.

Hypotension shadow over the cochlear bone in a patient of otosclerosis

Audiometry Tests

As the CT scan and Otoscope results in most cases of Otosclerosis leave the ENT with no clue to understand the type and extent of hearing loss, they opt for audiometry tests.

Audiometry test often reveals conductive deafness as a key indicator of otosclerosis.

Impedance Audiometry Test

Another diagnostic method is impedance audiometry, which assesses the impedances within the ear, offering valuable insights into the condition. One crucial parameter assessed in impedance audiometry is static compliance, which tends to be notably low in otosclerosis. The term "compliance" here refers to the flexibility of the ear structures, and in otosclerosis, the formation of new bone restricts this flexibility.

Is it Otosclerosis or Otospongiosis?

The distinction between stages, such as otospongiosis and otosclerosis, poses a challenge. Both involve new bone formation and differentiating between them requires a microscopic analysis of a tissue sample. This examination is typically only possible through surgery, where a small piece of tissue is extracted for further study under a microscope.

otosclerosis audiogram

otosclerosis tympanometry

Treatment of Otospongiosis and Otosclerosis

As mentioned earlier, the differentiation of treatment options for otosclerosis depends on the type of deafness present.

If nerve deafness is observed, hearing aids can be beneficial. For conductive deafness, surgical intervention, as well as hearing aids are good options.

Nerve Deafness - Hearing Aid

For nerve deafness, where bone movement is not impaired, hearing aids are recommended to rectify the hearing impairment.

Conductive Deafness - Surgery for Otosclerosis to reconstruct Stapes Bone

Conductive deafness, where nerve function is good, but bone movement is deranged, can be corrected by surgery. In this, a small hole is made in the stapes bone, and part of it is removed and connected to the incus in the middle ear using a Teflon prosthesis.

The surgery is done with a robotic laser, if available, where everything is done internally through the ear canal without cutting the skin. Surgery involves lifting the eardrum, replacing the stapes bone with the prosthesis, and repositioning the eardrum.

This procedure improves hearing by transmitting sound from the eardrum to the inner ear.

Both Conductive and Nerve Deafness – Should we opt for surgery?

If both nerve deafness and conductive deafness are present, the surgery results may give around 50% improvement. So for this, we will see if the airborne gap is more than 20 decibels, surgery is considered. But if the gap is less than 20 decibels, the patient may not appreciate the benefits of surgery, and it may not be necessary.

Cost of Surgery

Surgery, performed with a robotic laser, takes around 2 to 3 hours. The cost may range from 1,00,000 to 2,00,000 depending on the procedure and equipment used.

Otosclerosis and Otospongiosis Treatment

Fluoride therapy is an oral treatment given to strengthen bones. This therapy should only be given when individuals develop the condition to prevent the progression of the disease.

Fluoride therapy generally has no side effects when given in the proper ratio.

While it's not recommended during pregnancy, fluoride therapy can be administered after delivery. Ironically, many cases are hereditary, and many are triggered in women during pregnancy. Despite the known risk of hearing loss during this time, fluoride therapy, which could prevent the onset of the disease, cannot be given.

It's important to note that the treatment depends on the patient's condition, so the decisions about treatment should be made in consultation with an expert ENT doctor.

Complications

If the condition is left untreated, gradual hearing loss is inevitable. In cases of sensory neural-type hearing loss, even hearing aids may not provide benefits, necessitating the use of a cochlear implant.

Moreover, complications can arise if the surgery is not conducted in a meticulously sterile environment. Any bacteria entering the inner ear during surgery can lead to labyrinthitis, resulting in total deafness, dizziness, and various other complications. Given the proximity of the surgery to the facial nerve, responsible for eyelid and mouth movement, facial nerve paralysis may occur. Carelessness during the process of elevating and repositioning the eardrum may also cause a perforation of the eardrum.

Furthermore, there is a risk of middle ear infection. These complications highlight the importance of maintaining aseptic conditions and precision during the surgery.

Prevention

Individuals can effectively prevent and manage otosclerosis by following these steps and consulting an ENT doctor.

1. Using fluoride medication under the guidance of an experienced ENT doctor can effectively halt the progression of the condition.

2. Individuals with a family history should consult an ENT doctor and take this medication if they experience any of the symptoms, especially if their parents have the condition.

3. A pregnant woman should also be careful and consult an ENT doctor if they experience hearing loss, even the mildest one.

Dr. K. R. Meghanadh