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 **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.