A 38-year-old woman presents with a 2-week history of severe neck pain, fever (38.5°C), and progressive dysphagia. On examination, the thyroid is tender and enlarged. Laboratory findings show TSH 0.2 mIU/L (normal 0.4–4.0), free T4 8.5 ng/dL (normal 0.8–1.8), elevated ESR 78 mm/hr, and CRP 12 mg/dL. Thyroid ultrasound shows a hypoechoic, heterogeneous gland with reduced vascularity on Doppler. Which is the most likely diagnosis?

## Clinical Diagnosis: Subacute Granulomatous Thyroiditis ### Key Clinical Features **Key Point:** Subacute thyroiditis (de Quervain thyroiditis) is characterized by a triphasic course: thyrotoxicosis → euthyroidism → hypothyroidism, with prominent systemic inflammation. ### Diagnostic Triad in This Case | Feature | Finding | Significance | |---------|---------|---------------| | **Presentation** | Severe neck pain + fever | Hallmark of subacute thyroiditis; pain is exquisite and radiates to jaw/ear | | **Thyroid function** | TSH suppressed, elevated free T4 | Early thyrotoxic phase (destructive release of preformed hormone) | | **Inflammatory markers** | Markedly elevated ESR (78) + CRP | Disproportionately high; typical of viral-triggered inflammation | | **Ultrasound** | Hypoechoic, heterogeneous, reduced vascularity | Characteristic of granulomatous destruction; NOT diffuse hyperemia | | **Timeline** | 2-week acute onset | Subacute thyroiditis typically presents acutely over days–weeks | ### Pathophysiology 1. **Viral trigger** (often preceded by URI; coxsackievirus, mumps, adenovirus) 2. **Granulomatous inflammation** → destruction of thyroid follicles 3. **Phase 1 (Early):** Leakage of preformed T3/T4 → thyrotoxicosis with **suppressed TSH** 4. **Phase 2 (Middle):** Euthyroid phase as hormone stores deplete 5. **Phase 3 (Late):** Hypothyroidism if follicular damage is extensive; TSH rises **High-Yield:** The **suppressed TSH with elevated free T4** in the setting of **severe neck pain** is pathognomonic for the thyrotoxic phase of subacute thyroiditis. ### Differential Exclusions **Clinical Pearl:** In subacute thyroiditis, **radioiodine uptake is LOW** (unlike Graves disease, where uptake is high). This distinguishes destructive thyrotoxicosis from primary thyroid overproduction. ### Natural History - Most patients recover completely within 6–12 months - Transient hypothyroidism may require short-term levothyroxine - Recurrence rate ~2–5% [cite:Robbins 10e Ch 24]