Otosclerosis Flashcards
Define Otosclerosis
- Primary metabolic endochondral bone disease of the otic capsule and ossicles (limited to the otic capsule)
- Abnormal bone remodelling results in fixation of the ossicles (stapes predominantly) and resulting in conductive hearing loss
- May have SNHL component if the cochlea is involved
- Associated tinnitus (75%) and disequilibrium/vestibular symptoms (25%)
- Bilateral in 80%
What is the genetics, inheritance, epidemiology, and symptoms of otosclerosis?
Inheritance:
- Autosomal dominant
- Incomplete (40%) penetrance
Epidemiology:
- 10% caucasians have histologic changes, only 12% of these people are symptomatic
- 2:1 Female predilection
- 1:1 F:M ratio for true Histologic changes
- Contralateral ear affected in 80% of cases
- 60% people report family history
- Typical age of onset is 3rd decade of life
- May be accelerated by hormonal changes during pregnancy
Symptoms:
- CHL with possible SNHL component
- Many have paracusis of Willis due to CHL
What is Paracusis of Willis?
Patients with CHL will say they hear better in noisy rooms due to this phenomenon “paracusis of Willis”
- Thought to occur because people speak louder in noisy surroundings, while the CHL reduces background noise, thus improving the signal to noise ratio
- In SNHL there is loss of outer hair cells and therefore greater problems hearing in noise (?)
Describe Carhart’s notch and provide a theory for its appearance
Carhart Notch = Hallmark audiologic sign of otosclerosis characterized by a decrease in bone conduction thresholds of (relative, not absolute): - seen ONLY IN THE BONY LINE
1. 5dB at 500Hz
2. 10dB at 1000Hz
3. 15dB at 2000Hz
4. 5dB at 4000Hz
This is a mechanical artifact that reverses with stapes mobilization
Theory:
- Stapes fixation disrupts the normal ossicular resonance (2000Hz)
- Possible relation to resonant frequency of the EAC (2-3kHz)
- Normal compressional mode of bone conduction is disturbed because of relative perilymph immobility caused by stapes fixation (therefore bone conduction is not completely normal either in Otosclerosis)
https://entokey.com/audiological-evaluation-of-the-patient-with-otosclerosis/
What anatomic locations does otosclerosis occur most often?
- Fissula Ante Fenestrum (most common) - a small connective tissue-filled cleft in the otic capsule of the temporal bone, not typically visualized on CT
- Round Window Niche
- Anterior wall of IAC
- Medial wall of cochlear apex
- Area posterior to the cochlear aqueduct
- Region adjacent to the semicircular canals
- Posterior Stapes footplate
FRICKS
Fissula ante fenestrum
Round window niche
IAC medial wall
Cochlear apex medial wall
Kockler aKqueduct (area posterior to it)
SCC adjacent area
FAF: https://anatomypubs.onlinelibrary.wiley.com/cms/asset/6b3e800a-3118-4751-9600-3de6f5941877/ar24711-fig-0009-m.jpg
Vancouver Pg 280
What is the fissula ante fenestram?
Small connective tissue-filled cleft located where the tendon of the tensor tympani muscle turns laterally toward the malleus.
Anterior to the oval window, posterior to the cohleariform process
What is the classic sign of cochlear otosclerosis?
Halo sign of otosclerosis
- Lucency aroudn the cochlea on CT imaging as the sclerotic bone that replaces the otic capsule is less dense than the original bone
- Results in “outlining” of the labyrinth
- Note: findings with Paget’s or osteogenesis imperfecta can be very similar
Mixed HL (conductive and SNHL component)
- Usually starts as conductive (where there is still stapes otosclerosis) and as you develop cochlear otosclerosis the ABG start to narrow as the sensorineural component worsens
What are the Histopathologic stages of otosclerosis?
A. Otospongiosis phase (“active phase”):
- Definition: Osteoclastic absorption of normal otic capsule bone, creating pseudovascular spaces
- Cells involved: Histiocytes, osteoclasts, and osteoblasts
- Pathophysiology: Bone around blood vessels are resorbed, the vessels dilate, and the osteocytes lay down rich amorphous ground substance (rich blue color under H&E - “Blue Mantles of Manasse”) - actually found in 20% of normal temporal bones
B. Sclerotic phase:
- Formation of dense, fibrotic, sclerotic bone in areas of previous bony resorption
- Vascular channels narrowed due to bone deposition
- Overall the bone is less dense than original petrous otic capsule, hence “halo sign” on CT imaging
What are the different areas (foci) of involvement of the footplate in otosclerosis? What are these terminologies? 6
- Anterior focus (most common)
- Posterior focus
- Circumferential - footplate margin only
- Bipolar involvement - both anterior and posterior ends of footplate involved
- Biscuit footplate - Involvement of the entire footplate (only) making it solid (not annular ligament)
- Obliterative otosclerosis - entire footplate and annular ligament involvement
Vancouver Pg 280
What is the pathognomonic histologic sign in otosclerosis?
Blue Mantles of Manasse
Vancouver PG 281
What are the layers of the bone involved with otosclerosis?
- Always begins in endochondral bone
- Later can involve endosteal and periosteal layers of bone
https://upload.wikimedia.org/wikipedia/commons/8/89/607_Periosteum_and_Endosteum.jpg
What is the Flamingo or Schwartze’s sign?
Reddish/Vascular tingue to Promontory seen through TM in otospongiosis phase of otosclerosis (due to high vascularity of active bony resorption)
What are 5 differences between Paget’s disease and otosclerosis?
Paget’s disease = chronic bony disorder that causes increased osteoclastic bony resorption followed by increased osteoblastic activity, but eventually leads to a stage of malignant destruction of bone.
- Paget’s involves all bones of the skull and often see enlarged calvaria; whereas otosclerosis only involves temporal bone
- Paget’s onset 6th decade, otosclerosis onset usually 3rd
- Paget’s initially periosteal but eventually involves endosteal and endochondral layers; otosclerosis only involves endochondral involvement
- Paget’s rarely involves stapes footplate or ossicles
- Greater degree of SNHL seen in Paget’s
What is the differential for patient with suspected otosclerosis? 8
- Third window lesions (Perilymph fistula, Semicircular canal dehiscence)
- Malleus head fixation
- Paget’s disease of the temporal bone
- Osteogenesis imperfecta (1/2 develop stapes fixation)
- Congenital stapes fixation (be cautious in a young male with onset of hearing loss at birth)
- Chronic serous otitis media
- Tympanosclerosis
- Ossicular discontinuity
What is the difference between middle ear pathology (ie. otosclerosis) and third window pathology in the following categories:
1. Air bone gap
2. Bone conduction thresholds
3. Acoustic refluexes
4. VeMP
5. OAEs
6. Umbo velocity on laser doppler vibrometry
7. Sound/pressure induced vertigo
8. Imaging
9. Exploratory tympanotomy
- Air bone gap
- ME: 0-60dB, any frequencies
- TW: 0-60dB greatest in lower frequencies - Bone conduction thresholds
- ME: Usually normal or elevated
- TW: Can be negative (-5 to -20 or better) for frequencies below 2000Hz - Acoustic refluexes
- ME: Absent
- TW: Present - VeMP
- ME: Absent
- TW: Present, thresholds lower than normal, can have higher amplitude - OAEs
- ME: Absent
- TW: May be normal - Umbo velocity on laser doppler vibrometry
- Stapes fixation = normal; malleus fixation = low; Ossicular discontinuity = high
- TW: High-normal - Sound/pressure induced vertigo
- ME: Absent
- TW: May be present - Imaging
- ME: May show middle ear/otosclerotic anomalies
- TW: Third window pathology - Exploratory tympanotomy
- ME: Ossicular lesion
- TW: Normal ossicular mobility
What are the audiometric and tympanometric findings of Otosclerosis? How do they change depending on stage of disease?
A. Conductive hearing loss with Carhart’s notch in bony line (Carhart resolves after Stapedectomy)
- Early disease: CHL mainly at low frequencies due to stiffness effect (SSCD has greater HL initially)
- Late disease: Maximal CHL with flat audiogram ~50dB due mass effect
- Later: May see involvement of cochlea with High frequency SNHL (basal turn most commonly affected)
- Primary cochlear otosclerosis: “Cooke-bite pattern” with Mixed hearing loss
B. Tympanogram:
- Early: Normal
- Late: As tympanogram (from tympanosclerosis)
C. Stapedial reflex:
- Early: Normal or Diphasic Stapedial reflex (“Negative on/off effect”) - increased compliance at the onset and cessation of sound stimulus - can even be seen before any CHL
- Intermediate: Reduced acoustic reflex amplitudes, followed by Loss of ipsilateral stapedial reflex
- Late: Elevated contralateral thresholds, which lastly leads to Loss of ipsilateral and contralateral stapedial reflexes (sound stimulus doesn’t get to inner ear due to CHL)
5 Stages: ORICD
On/off effect
Reduced ipsilateral amplitudes
Ipsilateral loss
Contralateral elevated thresholds
Disappearance of reflex altogether
Kevan Otology Pg 45
What are 3 etiologies of SNHL in otosclerosis?
- Toxic metabolites in endolymph causing neuroepithelial damage
- Vascular compromise from narrowing and sclerosis of vascular channels
- Direct extension of lesion into inner ear, affecting basilar membrane biomechanics and electrolyte concentrations
What are the 6 indications for obtaining a CT in otosclerosis?
Maximal CHL with concerns of round window closure
Suspicion of superior semicircular canal dehiscence
Congenital CHL (x-linked stapes gusher)
Post-op vertigo (piston malposition)
Revision Stapes
Significant SNHL component
SCLERO
- S: Significant SNHL component
- C: Congenital CHL (x-linked stapes gusher)
- L: Loss of maximal conductive hearing (ie. Maximal CHL with concerns of round window closure)
- E: Extra window (Suspicion of superior semicircular canal dehiscnece)
- R: Revision Stapes
- O: Operative issues (Post-op vertigo/piston malposition)
What are the findings on imaging that can be seen with otosclerosis?
Otosclerosis is primarily a clinical diagnosis but CT temporal bones can be usedful in certain cases
Early:
- Lucency at the fissula ante fenestrum
Cochlear otosclerosis:
- Halo sign (demineralization of otic capsule bone)
Advanced cochlear otosclerosis:
- Increased density and thickening of sclerotic bone around the otic capsule
What are the 7 criteria for diagnosis of SNHL due to cochlear otosclerosis? What is the name of this criteria?
Shambaugh’s Criteria (to identify patients suffering from SNHL due to otosclerosis - 7 features)
- Positive Schwartze’s sign in either ear
- Family history of surgically confirmed by stapedial otosclerosis
- Unilateral CHL consistent with otosclerosis and bilateral symmetric SNHL
- Audiogram with a flat or cookie bite curve with better than expected word discrimination for degree of SNHL
- Progressive pure cochlear loss beginning at the usual age of onset for otosclerosis
- CT scan in patient with one or more of above criteria that shows cochlear capsule demineralization (negative scan does not preclude diagnosis because mature disease resembles normal bone on CT)
- On-Off effect on impedance tympanometry
“HAS CUPS” HAS (clinical), CUPS (audiometric)
H: Halo Sign
A: Autosomal dominant (family history)
S: Schwartze sign
C: Cookie bite or flat audiogram with better than expected speech discrimination for degree of hearing loss
U: UNilateral CNHL consistent with OS with concomitant bilateral symmetric SNHL
P: Progressive pure cochlear loss beginning at expected age of onset for OS
S: Stapedial reflexes - diphasic on-off effect
Discuss the overall management options of otosclerosis
- Clinical observation and serial audiometry
- Trial of Hearing Amplification
- Medial Management
- Sodium Fluoride
- Bisphosphonates - Surgery (elective surgery, should have negative Rinne with 512 Hz fork)
- Stapes mobilization
- Stapedotomy (better high frequency)
- Stapedectomy (better low frequency)
- BAHA
What are the indications of sodium fluoride use in otosclerosis?
INDICATIONS:
1. Presence of SNHL or vertigo (cochlear otosclerosis)
2. Non-surgical candidates
3. Positive Schwartze’s sign pre-op (treat for 6 months prior to surgery to achieve stability)
4. Otospongiosis type bone seen intraoperatively
“NAFL”: (Stands for Sodium Fluoride)
N: Non-surgical candidates
A: Active disease/resorption of bone (Otospongiosis type bone seen intraoperatievly)
F: Flamingo (Schwartze’s sign) pre-op (sign of active disease)
L: Loss of Hearing (SNHL or vertigo - symptoms of cochlear otosclerosis)
Regarding Sodium fluoride for the treatment of otosclerosis, discuss:
1. Pathophysiology
2. Treatment regimen and dose
3. Side effects
4. Contraindications
PATHOPHYSIOLOGY:
- Thought to stabilize hearing loss associated with otosclerosis by 80%
- Replaces the usual hydroxyl ion in perosteal bone forming fluoroapatite (instead of hydroxyapatite) - fluoroapatite is less soluble than hydroxyapatite and is stronger/more resistant to demineralization/absorption (think fluoride in toothpaste)
- Effects: Reduces/slows bone resorption, encourages bone formation, clears Schwartz sign, and inactivates expanding foci of otosclerosis
TREATMENT REGIMEN/DOSE:
- Available over the counter as “Florical”
- Taken with Vitamin D and calcium gluconate
- 20-120mg daily x 1-2 years during active disease, can be used pre-operatively x6-12 months to achieve stability
- Can step down to 25mg daily maintenance dose long term
- Stopping treatment in patients whose disease has stabilized on therapy may result in reactivation in 2-3 years
SIDE EFFECTS:
1. Rash
2. Arthritis
3. Gastric distress
CONTRAINDICATIONS:
1. Pregnancy
Discuss the use of bisphosphonates in otosclerosis treatment.
What is the mechanism of action?
What is the main risk?
3rd generation bisphosphonates used (Alendronate (Fosamax))
- MOA: Inhibit osteoclastic bone resorption, attaches to hydroxyapatite binding sites on bony surfaces
- Has been tried with variable results
- Some weak evidence that it might decrease progression of SNHL
- Small risk of ORN of the mandible
