Which is the most common cause of thyroiditis worldwide?

Question

Accepted Answer

C. Hashimoto thyroiditis. ## Most Common Thyroiditis: Hashimoto Thyroiditis

### Epidemiology and Prevalence

**Key Point:** Hashimoto thyroiditis (chronic autoimmune thyroiditis) is the most common cause of thyroiditis and the leading cause of hypothyroidism in iodine-sufficient regions worldwide.

**High-Yield:** In India and other iodine-sufficient countries, Hashimoto thyroiditis accounts for approximately 60–70% of all thyroiditis cases and is the most frequent autoimmune endocrine disorder.

### Pathophysiology

Hashimoto thyroiditis is a cell-mediated and antibody-mediated autoimmune disorder characterized by:
- Infiltration of thyroid by lymphocytes and plasma cells
- Formation of germinal centers
- Destruction of thyroid follicles
- Fibrosis in advanced stages
- Positive anti-TPO (thyroid peroxidase) and anti-thyroglobulin antibodies

### Clinical Presentation

- Insidious onset of hypothyroidism
- Diffuse firm goiter (may be absent in atrophic variant)
- Female predominance (5–10:1)
- Peak incidence: 30–50 years
- Associated with other autoimmune conditions (celiac disease, type 1 diabetes, pernicious anemia)

### Comparison with Other Thyroiditis Types

| Feature | Hashimoto | De Quervain | Graves | Riedel |
|---------|-----------|-------------|--------|--------|
| **Frequency** | Most common | Uncommon | Autoimmune but not thyroiditis | Rare |
| **Etiology** | Autoimmune | Viral (post-viral) | Autoimmune (TSH-R antibodies) | Idiopathic fibrosis |
| **Presentation** | Insidious hypothyroidism | Acute thyroiditis + pain | Hyperthyroidism | Fibrosis + hypothyroidism |
| **Antibodies** | Anti-TPO, anti-Tg | Absent | TSI (TSH receptor) | Absent |
| **Prognosis** | Permanent hypothyroidism | Self-limited | Relapsing-remitting | Progressive fibrosis |

**Clinical Pearl:** Graves disease is an autoimmune disorder causing hyperthyroidism, but it is NOT classified as thyroiditis because it does not involve inflammation of the thyroid tissue itself — it is mediated by stimulating antibodies (TSI) rather than destructive inflammation.

**Warning:** De Quervain (subacute granulomatous) thyroiditis is the second most common cause of symptomatic thyroiditis, but it is self-limited and accounts for only 5–15% of thyroiditis cases. It is often confused with Hashimoto in exams, but its viral etiology and acute presentation distinguish it.

**Mnemonic:** HASH = **H**ashimoto is **A**utoimmune, **S**low (insidious), **H**ypothyroidism (outcome).

### Why Hashimoto Is Most Common

1. **Genetic predisposition:** HLA-DR3, HLA-DR4, HLA-DR5 associations
2. **Environmental triggers:** Iodine intake, infections, stress
3. **Female predominance:** Estrogen-mediated immune response
4. **Chronic nature:** Persistent autoimmune attack leads to long-term prevalence

[cite:Robbins 10e Ch 24]

Answer

A. De Quervain thyroiditis

Answer

B. Graves disease

Answer

D. Riedel thyroiditis

Which is the most common cause of thyroiditis worldwide?

Explanation

Most Common Thyroiditis: Hashimoto Thyroiditis

Epidemiology and Prevalence

Pathophysiology

Clinical Presentation

Comparison with Other Thyroiditis Types

Why Hashimoto Is Most Common

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Feature	Hashimoto	De Quervain	Graves	Riedel
Frequency	Most common	Uncommon	Autoimmune but not thyroiditis	Rare
Etiology	Autoimmune	Viral (post-viral)	Autoimmune (TSH-R antibodies)	Idiopathic fibrosis
Presentation	Insidious hypothyroidism	Acute thyroiditis + pain	Hyperthyroidism	Fibrosis + hypothyroidism
Antibodies	Anti-TPO, anti-Tg	Absent	TSI (TSH receptor)	Absent
Prognosis	Permanent hypothyroidism	Self-limited	Relapsing-remitting	Progressive fibrosis