A 32-year-old woman presents with acute onset severe thyroid pain, fever, and dysphagia 2 weeks after an upper respiratory tract infection. Thyroid function tests show suppressed TSH and elevated free T4. All of the following are consistent with acute (suppurative) thyroiditis EXCEPT:

Question

Accepted Answer

B. Presence of anti-TPO antibodies and positive thyroid peroxidase antibody titers. ## Acute (Suppurative) Thyroiditis — Diagnostic Features

### Correct Answer: Presence of anti-TPO antibodies and positive thyroid peroxidase antibody titers

**Key Point:** Acute suppurative thyroiditis is a **bacterial infection** of the thyroid, not an autoimmune condition. Anti-TPO antibodies are characteristic of autoimmune thyroiditis (Hashimoto), not bacterial infection. The presence of these antibodies would suggest an autoimmune process, not acute suppurative thyroiditis.

### Acute Suppurative Thyroiditis — Pathological & Clinical Features

| Feature | Present | Notes |
|---------|---------|-------|
| Bacterial infection | ✓ Yes | S. aureus, S. pyogenes, E. coli, anaerobes |
| Acute inflammation | ✓ Yes | Neutrophilic infiltrate, abscess formation |
| Fever & systemic toxicity | ✓ Yes | Acute presentation |
| Elevated ESR/CRP | ✓ Yes | Acute phase response |
| Ultrasound findings | ✓ Yes | Hypoechoic areas, abscess, fluid collections |
| Anti-TPO antibodies | ✗ No | **Autoimmune marker — not present in bacterial infection** |
| Thyroid dysfunction | ✓ Yes | Thyroiditis phase (suppressed TSH, high T4) |

### Clinical Pearl

**High-Yield:** Acute suppurative thyroiditis is **rare** (< 1% of thyroid diseases) because:
1. The thyroid has a rich blood supply and lymphatic drainage
2. The gland is well-encapsulated
3. Iodine content has antimicrobial properties

When it occurs, it is often associated with:
- Immunocompromise (HIV, chemotherapy)
- Anatomical defects (pyriform sinus fistula — most common predisposing factor)
- Hematogenous spread from distant infection

### Differential: Autoimmune vs. Infectious Thyroiditis

| Feature | Hashimoto (Autoimmune) | Acute Suppurative (Bacterial) |
|---------|------------------------|-------------------------------|
| **Antibodies** | Anti-TPO, anti-Tg | Absent |
| **Infiltrate** | Lymphocytes + germinal centers | Neutrophils + abscess |
| **Onset** | Insidious (weeks–months) | Acute (days) |
| **Fever** | Absent | Present |
| **Pain** | Mild or absent | Severe |
| **Culture** | Sterile | Positive for bacteria |
| **ESR/CRP** | Mild elevation | Marked elevation |

**Warning:** Do not confuse acute suppurative thyroiditis with subacute (de Quervain) thyroiditis — subacute is viral, self-limited, and does NOT have abscess formation or positive cultures.

Answer

A. Elevated erythrocyte sedimentation rate and C-reactive protein

Answer

C. Thyroid ultrasound shows hypoechoic areas with abscess formation

Answer

D. Causative organism is typically Staphylococcus aureus or Streptococcus pyogenes

A 32-year-old woman presents with acute onset severe thyroid pain, fever, and dysphagia 2 weeks after an upper respiratory tract infection. Thyroid function tests show suppressed TSH and elevated free T4. All of the following are consistent with acute (suppurative) thyroiditis EXCEPT:

Explanation

Acute (Suppurative) Thyroiditis — Diagnostic Features

Correct Answer: Presence of anti-TPO antibodies and positive thyroid peroxidase antibody titers

Acute Suppurative Thyroiditis — Pathological & Clinical Features

Clinical Pearl

Differential: Autoimmune vs. Infectious Thyroiditis

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Feature	Present	Notes
Bacterial infection	✓ Yes	S. aureus, S. pyogenes, E. coli, anaerobes
Acute inflammation	✓ Yes	Neutrophilic infiltrate, abscess formation
Fever & systemic toxicity	✓ Yes	Acute presentation
Elevated ESR/CRP	✓ Yes	Acute phase response
Ultrasound findings	✓ Yes	Hypoechoic areas, abscess, fluid collections
Anti-TPO antibodies	✗ No	Autoimmune marker — not present in bacterial infection
Thyroid dysfunction	✓ Yes	Thyroiditis phase (suppressed TSH, high T4)

Feature	Hashimoto (Autoimmune)	Acute Suppurative (Bacterial)
Antibodies	Anti-TPO, anti-Tg	Absent
Infiltrate	Lymphocytes + germinal centers	Neutrophils + abscess
Onset	Insidious (weeks–months)	Acute (days)
Fever	Absent	Present
Pain	Mild or absent	Severe
Culture	Sterile	Positive for bacteria
ESR/CRP	Mild elevation	Marked elevation