Otosclerosis Part 1 - Causes, Pathogenesis, Types, Pathology

🦴 Otosclerosis — Definition, Etiopathogenesis & Histopathology

Otosclerosis is a high yield ENT topic, especially for vivas and MCQs.

🚩 A typical exam question describes:

• A middle aged female
• Progressive conductive hearing loss
• Often worsens during pregnancy

This topic is covered as a three part series:

1. Part 1: Definition, etiopathogenesis & histopathology
2. Part 2: Clinical features & investigations
3. Part 3: Treatment

🧠 What is Otosclerosis?

Otosclerosis is a hereditary disorder of bone metabolism involving the otic capsule and chondral bone, characterized by abnormal bone remodeling.

What is the key pathology seen in Otosclerosis?

What is the most commonly involved site in Otosclerosis?

📊 Epidemiology of Otosclerosis

• Affects 0.5–1% of the population

• Onset: 20–30 years

• Rare before 10 years and after 40 years

• Female : Male = 2 : 1

• Usually bilateral (≈85%)

• More common in:

  • Whites
  • Indians

• Rare in:

  • Africans
  • Chinese & Japanese

Why is Otosclerosis seen more commonly in middle aged females?

🧩 Types of Otosclerosis

Broadly classified into:

• Clinical otosclerosis
• Histological otosclerosis

👂 A. Clinical Otosclerosis

Lesions cause clinical symptoms due to involvement of:

• Stapes
• Stapediovestibular joint
• Cochlea
• Round window

🔹 Subtypes

1. Stapedial otosclerosis
2. Cochlear otosclerosis
3. Mixed otosclerosis

1. Stapedial Otosclerosis

• Most common type
• Causes stapes fixation
• Presents with conductive hearing loss
• Most common site - fissula ante fenestram

What are the different sites of lesion in stapedial otosclerosis?

What is Biscuit type of Otosclerosis?

What is Circumferential type of Otosclerosis?

What is Obliterative type of Otosclerosis?

2. Cochlear Otosclerosis

• Lesions involve cochlear endosteum

• Rare compared to stapedial type

Is there stapes involvement in Cochlear Otosclerosis?

What type of hearing loss is seen in Cochlear Otosclerosis?

What is Malignant Otosclerosis?

3. Mixed Otosclerosis

• Involves both stapes and cochlea
• Causes mixed hearing loss

🔬 B. Histological Otosclerosis

• Lesions present histologically

• No clinical symptoms

• Detected post-mortem

• Accounts for 9–12% of cases

🧬 Etiology & Risk Factors of Otosclerosis

Exact cause unknown, but several factors implicated.

🧬 Genetic Factors

• 50% familial, 50% sporadic

What pattern of inheritance is seen in Otosclerosis?

What are the genes involved in Otosclerosis?

🦠 Viral Hypothesis

• Measles virus antigens found in active lesions
• Increased CD46 receptor expression
• Lower anti-measles IgG levels reported

What are the Limitations of viral hypothesis for Otosclerosis?

🧫 Autoimmune Factors

• Possible immune reaction against type II collagen

• Cytokines involved:

  • TGF-β1
  • Bone morphogenetic proteins (BMP)

🧪 Hormonal Factors

• Worsening during pregnancy

• Progression during menopause

• Explains female predominance

🧬 Syndromic Association (MCQ Alert 🚨)

Van der Hoeve Syndrome

What is Van der Hoeve Syndrome? What is the triad seen in Van der Hoeve Syndrome?

🔄 Pathogenesis of Otosclerosis

Etiological factors act on:

• Otic capsule
• Labyrinthine capsule

🧠 Key events in Otosclerosis

1. Enlargement of perivascular spaces
2. Bone resorption by osteoclasts
3. New bone deposition by osteoblasts
4. Neovascularization & vascular shunting
5. Thickened mucoperiosteum

➡️ Produces Schwartz sign.

Describe the pathogenesis of Otosclerosis.

What is Schwartz sign? What is it indicative of?

🧫 Gross Pathology of Otosclerosis

• Lesions appear:
  • Chalky white
  • Grey / yellow
  • Red (active lesions)

🔬 Histopathology of Otosclerosis

Two phases:

1. Early Spongiotic Phase
2. Late Sclerotic Phase

What are the histopathological changes seen in the Early Spongiotic Phase of Otosclerosis?

What are the histopathological changes seen in Late Sclerotic Phase of Otosclerosis?

🧪 Active vs Inactive Otosclerotic Lesions

🔵 Active Otosclerotic Lesions

• Spongy bone
• Osteoclasts
• Dilated vessels
• Blue mantles of Manasse

What are the Blue mantles of Manasse seen in Otosclerosis?

🔴 Inactive Otosclerotic Lesions

• Dense compact bone
• Minimal vascularity
• Fibrous tissue predominance

📌 Key Exam Pearls

• Middle aged female + Conductive Hearing Loss → Think Otosclerosis
• Commonest site: Fissula ante fenestram
• Schwartz sign = active lesion
• Blue mantles of Manasse = spongiotic phase
• Van der Hoeve syndrome = MCQ favorite

📘 Next Part:
Clinical features, audiological findings & diagnosis of otosclerosis.