Otosclerosis: Types, Symptoms, Diagnosis, Treatment

Oto means ear and sclerosis means excessive bone deposition  This disease affects the middle ear (ossicles of the middle ear or stapes footplate). Otosclerosis is a type of abnormal middle ear bone growth that results in progressive hearing loss. Additionally, there may be a loss of equilibrium. The etiology is unknown, although risk factors include gender, pregnancy, and family history. Surgery and hearing aids are available as treatment alternatives.

Labyrinth

The labyrinth or the inner ear has got two parts: the outer bony part and the inner membranous part. The vestibule is the central chamber of the labyrinth. The cochlea is present anteriorly and the semicircular canals posteriorly. It is a disease of bony labyrinth. In this normal endochondral bone of the otic capsule is replaced by irregularly placed spongy bone.

It's a disease of the bony labyrinth.  Normal Endochondral bone of Otic capsule is replaced by irregularly placed spongy bone. The sound waves enter the external auditory canal and reach the tympanic membrane. After the tympanic membrane, it goes via the ear ossicle. The first ear ossicle is the malleus, the second is the incus and the third one is the stapes. The stapes cover the footplate, and from the footplate, the sound waves reach the oval window, scala vestibuli, via helicotrema to the scala tympani. From the scala tympani, the sound waves come and hit the round window. The basilar membrane carries the impulses from the cochlea via the auditory pathway to the brain. In otosclerosis, there is excessive deposition of bone around the footplate of the stapes. So, the sound waves cannot be conducted from the external or middle ear to the inner ear, resulting in hearing loss.

Any pathology that falls from the pinna to the footplate of the middle ear (conductive pathway) results in conductive hearing loss. The footplate is present on the oval window and stapes cover the oval window. Stapedial otosclerosis is the most common type of otosclerosis.

Site of Stapedial Otosclerosis

The most common site for stapedial otosclerosis is the fistula ante fenestrum, which means anterior to the footplate. To understand anterior and posterior regions, look for pyramidal eminence and stapedial tendon. The pyramidal eminence is on the posterior wall of the middle ear, from here there is a stapedial tendon attached to the neck of the stapes.

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Types of Otosclerosis

1. Stapedial: It is  Most common. Fistula ante fenestrum common site it leads to Conductive hearing loss.
2. Cochlear: Round window common site. It causes Sensorineural  hearing loss and tinnitus
3. Histological type

Aetiology

• Hereditary – Autosomal dominant with incomplete penetrance 
• Sex: F>M but in India male predominant 
• Age of onset:  20-40 years
• Hormonal – Increases in pregnancy and during menopause

Trigger factors for otosclerosis

• Progesterone excess
• Oral contraceptive pills (OCP)
• Measles infection
• Autoimmune disorders

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Syndrome associated with otosclerosis

Vander Hoeve syndrome

• Osetogenesis Imperfecta: Collagen disease leading to weak bones with conductive hearing loss.
• Otosclerosis
• Blue sclera

Otosclerosis Lesion

Excessive bony disposition appears as whitish plaque on the footplate of the stapes. Normally, the footplate of stapes has three layers, outer periosteal, middle endochondral layer, And an endosteal layer inside. The triggers for otosclerosis stimulate the endochonrdal cell rests. These cells proliferate osteoclasts,  which cause bone resorption. Due to resorption there is increased vascular activity due to release of proteolytic enzymes, resulting in bone destruction. Remodeling, carried out by osteoblasts, happens  whenever there is osteoclastic activity.  The newly formed bone is spongy with increased vascularity and marrow spaces. The spongy bone slowly replaces the healthy bone, and the food plate becomes inactive(scelrotic bone) and cannot move. On H & E stain, it will appear blue due to increased vascularity, osteoclastic and osteoblastic activity, referred to as BLUE MANTLE OF MANASSE. 

Active lesions: Occurs when the trigger has occurred seen in the initial part of the disease when disease proliferates It shows numerous spongy or irregular bones, along with increased vascularity and blood vessels  There is also an increased number of osteoclasts and blasts. Inactive lesion: it is the end stage of disease we see solid sclerotic bone. Once the disease has reached the end stage, the progression cannot be prevented.

Symptoms

Most common presenting feature:

• Conductive hearing loss ( bilateral)
• Mixed hearing loss when lesion extend to scala vestibuli
• Tinnitus when lesion extended to cochlea
• Paracusis willisii: Person hear better in noisy environment.
  it is a feature of stapedial otosclerosis
• Sometimes the deposition of bone can reach the scala vestibuli of cochlea and results in conductive as well as sensory neural components of hearing loss, referred to as mixed hearing loss.
• CHL and paracusis willisii (hearing better in the noisy environment rather than a silent environment) are commonly seen in the stapedial type of otosclerosis.
• No ear pain and ear discharge.
• Typically seen in middle-aged individuals.

Symptoms of Cochlear Otosclerosis

1. Sensorineural Hearing loss
2. Tinnitus

Paracusis Willisii: Hears better in noisy than in quiet environment 

Signs

• Tympanic membrane is normal [90%]
• Tympanic membrane is mobile
• Schwartz Sign [10%]
• Active lesions have a flamingo-pink hue on the promontory and can be seen through an intact tympanic membrane.
• Stapes is fixed, and the tympanic membrane is fixed, although mobility can be restricted.
• Swhartz sign: In active otosclerotic lesion, because of increased vascularity, the mucoperiosteum covering the inner ear, the bony labyrinth becomes red. Through the tympanic membrane, i appears flamingo pink.

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Stapedial Otosclerosis: Tests

• Rinne Test: The bone conduction(BC) is better than the air conduction(AC). When the tuning fork is placed on the mastoid, the patient will hear better as compared to air conduction.
• Weber Test: When the tuning fork is kept on the midline, the patient feels that the sound is getting lateralised to a diseased ear or abnormal ear. 
• Absolute bone conduction test is done for sensory neural pathway problems and here there is only conductive hearing loss hence it is normal.
• Gelle’s Test: When the pressure is increased or decreased on the external auditory canal and sound stimulation is given, the patient should be able to appreciate the increase and decrease in the intensity of sound. When the patient is unable to do this, the test is negative. And the patient is having otosclerosis.
• In tympanometry As-type of graph is seen, where s stands for sclerosis. It is most specific for otosclerosis.
• Stapedial reflex is absent because the stapes is not able to move because of its fixation.

Audiometry

• Air Conduction - In this  Lower frequencies are affected.
• Bone Conduction – Maximum dip is seen at 2000 Hz which is called Carhart's notch.
• Reverses after Stapedectomy
• In audiogram X indicates air conduction of the left ear, and ] indicates bone conduction.
• AC is in the abnormal range and BC is in the normal range with a gap known as AB (air-bone) gap.The AB gap is diagnostic of conductive hearing loss.
• Carhart's notch is a dip seen at 2000 Hz in bone conduction in otosclerosis but it disappears after Stapedectomy.

Cochlear Otosclerosis: Tests

• Here AC>BC
• In cochlear otosclerosis there is sensorineural hearing loss

Cochlear Otosclerosis

• COOKIE BITE CURVE – A dip in the mid frequency range of both AC and BC is called cookie bite curve 0 here indicates Air conduction of the right ear.  Here indicates Bone conduction of the right ear.
• In the middle frequency (1k and 2k) there is a dip in both AC and BC Indicating SNHL.

Treatment

• Medical:
  • Hearing aid: It is offered to all patients.
  • Sodium fluoride
    • It is given to arrest active focus and prevent further sensorineural loss due to cochlear otosclerosis

Sodium Fluoride

Sodium fluoride is only given in an active lesion to stop the further progression of an existing hearing loss. It inhibits the osteoclast and release of proteolytic enzymes. This further inhibits bone destruction. So, there is no further bone remodeling and no new bone deposition.

Contraindication – 

• Pregnancy and lactation
• Renal disease
• Rheumatoid arthritis
• Skeletal fluorosis

Sodium fluoride is only given in an active lesion to stop the further progression of an existing hearing loss. It inhibits the osteoclast and release of proteolytic enzymes. This further inhibits bone destruction. So, there is no further bone remodeling and no new bone deposition.

• Surgical:
  • Stapedectomy with the placement of a prosthesis is the treatment of choice 
  • Stapedotomy and placement of prosthesis
  • Stapes mobilization
  • Lemperts Fenestration operation: reserved only for cases where footplate cannot be mobilized during stapedectomy

Speech discrimination indicates that the sensory neural pathway should be normal. Surgery carries the chances of complications so it should be avoided if the ear is only hearing ear. In occupations like pilots and drivers, due to barotrauma the piston can get replaced so surgery should be avoided, or they can be asked to change professions after surgery.

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Local Anesthesia or General Anesthesia?

Local anesthesia versus General anesthesia Local Anesthesia is preferred over general anesthesia: To assess the improvement in hearing: The stapes are removed and replaced with a piston, ideally the piston should enter the incus and touch the oval window snuggly. It varies from person to person. It is measured intraoperatively To assess complication: the facial nerve runs just above the oval window. So, the signs can be easily assessed under local anesthesia. To assess perilymph fistula: The stapes footplate covers the oval window, which covers the scala vestibuli of the cochlea containing perilymph. When the footplate or oval window is operated, there is a possibility of leakage of perilymph from the oval window.  When the fine area is operated there can be oval window tears and the perilymph may leak and come into the middle ear. This can result in vertigo and nausea.

Stapedotomy

 An endoral or endomeatal approach from the external auditory canal is used in the procedure. The tympanomeatal flap is elevated and firstly the mobility of ear ossicles is tested. The stapes are fixed. The incus is dislocated from the stapes suprastructure.Craniectomy: Anterior crura and posterior crura are dislocated and the suprastructure is taken out. A hole is made in the footplate. A piston is anchored from the incus to the stapes. The sound is now conducted from malleus incus and through the piston to the oval window. If the footplate is removed, it is known as stapedectomy. Stapedectomy has higher chances of perilymph leak, because, during the removal of the footplate, the perilymph may leak out due to tear. There is less chance of recurrence of the disease as footplate is removed. Stapedectomy is the preferred surgical procedure. In stapedotomy, only a hole is made in the footplate and it is intact , so there are less chances of perilymph leak. The chances of recurrence of disease are higher as the footplate is intact.

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Complications

• Perilymph Fistula due to tearing of the oval window.
• Recurrence due to displacement of prosthesis or due to new bone deposition in stapedotomy.
• Necrosis of Incus when the piston is fixed tightly leading to compromised blood supply.
• Facial palsy because the facial nerve lies close to the foot plate area.

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