A 28-year-old woman presents with acute onset of severe neck pain, fever, and palpitations for 3 days. Examination reveals a tender, enlarged thyroid. Thyroid function tests show suppressed TSH with elevated free T4. Which is the most common cause of acute thyroiditis in this clinical presentation?

Explanation

## Acute Thyroiditis: De Quervain Thyroiditis ### Clinical Presentation Recognition **Key Point:** De Quervain (subacute granulomatous) thyroiditis is the most common cause of **acute symptomatic thyroiditis** presenting with sudden onset of severe neck pain, fever, and signs of thyroid inflammation. **High-Yield:** The triad of acute thyroiditis presentation is: (1) severe neck pain, (2) fever, (3) thyroid tenderness. This clinical picture is pathognomonic for De Quervain thyroiditis. ### Pathophysiology 1. **Etiology:** Post-viral inflammation (mumps, influenza, adenovirus, EBV, CMV) 2. **Pathology:** Granulomatous inflammation with giant cells and follicular destruction 3. **Mechanism:** Viral infection triggers thyroid inflammation → follicular disruption → release of preformed thyroid hormones → transient thyrotoxicosis 4. **Timeline:** Self-limited course over 4–12 weeks ### Clinical Phases ```mermaid flowchart TD A[Viral infection]:::outcome --> B[Phase 1: Thyroiditis<br/>Acute pain + fever]:::action B --> C[Follicular destruction]:::outcome C --> D[Phase 2: Thyrotoxicosis<br/>High T4, suppressed TSH]:::outcome D --> E[Phase 3: Hypothyroidism<br/>Low T4, high TSH<br/>2-8 weeks]:::outcome E --> F[Phase 4: Recovery<br/>Normal function]:::outcome ``` ### Diagnostic Features | Feature | De Quervain | Hashimoto | Suppurative | |---------|-------------|-----------|-------------| | **Onset** | Acute (days) | Insidious (months–years) | Acute (hours–days) | | **Pain** | Severe, neck pain | Absent or mild | Severe, localized | | **Fever** | Present | Absent | High fever, sepsis | | **Thyroid tenderness** | Marked | Absent | Marked, fluctuant | | **ESR/CRP** | Markedly elevated | Normal/mildly elevated | Elevated | | **Antibodies** | Absent (TPO/Tg negative) | Present (TPO+, Tg+) | Absent | | **Thyroid function** | Thyrotoxic phase early | Hypothyroid | Variable | | **Ultrasound** | Heterogeneous echotexture | Hypoechoic, diffuse | Focal abscess/collection | | **Culture** | Sterile | Sterile | Positive (S. aureus, streptococci) | **Clinical Pearl:** The presence of **suppressed TSH with elevated free T4** in the acute phase is characteristic of De Quervain thyroiditis, reflecting the thyrotoxic phase from follicular disruption and hormone release, not true thyroid hyperfunction. **Warning:** Hashimoto thyroiditis presents insidiously over months to years with progressive hypothyroidism, NOT acute pain and fever. It is a chronic autoimmune condition, not an acute inflammatory process. **Warning:** Suppurative (bacterial) thyroiditis is rare and usually follows a focus of infection (pharyngitis, dental abscess) or is secondary to immunosuppression. It presents with localized abscess formation and positive culture, not the self-limited course of De Quervain. **Mnemonic:** **DeQ** = **De** Quervain is **Qu**ick (acute), **Q**uells (self-limited), **Q**uintessential post-viral thyroiditis. ### Management 1. **NSAIDs:** First-line for pain and inflammation (ibuprofen, naproxen) 2. **Beta-blockers:** For symptomatic thyrotoxicosis (propranolol) 3. **Corticosteroids:** Reserved for severe cases or NSAID failure (prednisolone 40 mg tapering) 4. **Levothyroxine:** Only if hypothyroidism persists beyond 6–12 weeks 5. **Supportive care:** Rest, hydration ### Prognosis - **Self-limited:** Complete resolution in 4–12 weeks in >90% of cases - **Recurrence:** Rare (<5%) - **Permanent hypothyroidism:** Uncommon (<5%) [cite:Harrison 21e Ch 405]