A 38-year-old woman presents with a 3-week history of severe anterior neck pain, fever, and malaise. She reports a recent upper respiratory tract infection 2 weeks ago. On examination, the thyroid is tender and firm. Laboratory investigations show TSH 0.2 mIU/L (normal 0.4–4.0), free T4 8.5 ng/dL (normal 0.8–1.8), elevated ESR 68 mm/hr, and CRP 12 mg/dL. Thyroid ultrasound shows heterogeneous echotexture with hypoechoic areas. Fine needle aspiration cytology reveals granulomatous inflammation with multinucleated giant cells. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: De Quervain Thyroiditis ### Key Clinical Features **Key Point:** De Quervain (subacute granulomatous) thyroiditis is characterized by the triad of: 1. Severe anterior neck pain (often radiating to jaw/ears) 2. Recent viral prodrome (URI, mumps, measles, influenza) 3. Thyrotoxic phase followed by hypothyroid phase ### Laboratory & Imaging Findings | Feature | De Quervain | Hashimoto | Riedel | Acute Suppurative | |---------|-------------|-----------|--------|-------------------| | **Onset** | Acute (days–weeks) | Insidious (months) | Insidious | Acute | | **Neck pain** | Severe, prominent | Absent | Mild/absent | Severe, localized | | **ESR/CRP** | Markedly elevated | Normal/mild ↑ | Markedly elevated | Markedly elevated | | **FNAC** | Granulomas, giant cells | Lymphocytes, Hürthle cells | Fibrosis, few cells | PMN infiltrate, bacteria | | **Viral prodrome** | Yes (typical) | No | No | No | | **TSH phase** | Suppressed (thyrotoxic) | Elevated (hypothyroid) | Elevated | Variable | **High-Yield:** The presence of **granulomatous inflammation with multinucleated giant cells** on FNAC is pathognomonic for De Quervain thyroiditis and distinguishes it from other forms. ### Pathophysiology ```mermaid flowchart TD A[Viral infection<br/>URI, mumps, measles]:::outcome --> B[Viral-induced thyroid inflammation] B --> C[Destruction of thyroid follicles] C --> D[Release of preformed thyroid hormones] D --> E[Thyrotoxic phase<br/>TSH suppressed, high T4/T3]:::outcome E --> F{Follicular recovery?}:::decision F -->|Yes| G[Hypothyroid phase<br/>TSH elevated, low T4]:::outcome F -->|No| H[Return to euthyroid state] C --> I[Granulomatous reaction<br/>Giant cells, lymphocytes] I --> J[FNAC findings]:::outcome ``` ### Clinical Course **Clinical Pearl:** De Quervain thyroiditis typically follows a **triphasic course**: 1. **Thyrotoxic phase** (weeks 1–4): TSH suppressed, elevated free T4/T3 due to hormone release 2. **Hypothyroid phase** (weeks 4–12): TSH elevated, low T4 as stores deplete 3. **Recovery phase**: Gradual normalization of thyroid function (usually complete within 6 months) ### Why This Case Fits De Quervain - **Recent viral prodrome** (URI 2 weeks prior) - **Severe anterior neck pain** (pathognomonic feature) - **Thyrotoxic biochemistry** (suppressed TSH, elevated free T4) - **Markedly elevated inflammatory markers** (ESR 68, CRP 12) - **Granulomatous FNAC** (diagnostic) - **Heterogeneous ultrasound** (patchy inflammation) ### Management **Key Point:** NSAIDs (aspirin, ibuprofen) are first-line for pain and inflammation. Severe cases or those with significant thyrotoxicosis may require short-course corticosteroids (prednisolone 20–40 mg daily, tapered over 4–6 weeks). Beta-blockers manage thyrotoxic symptoms. Antithyroid drugs (PTU, methimazole) are **NOT indicated** because thyrotoxicosis is due to hormone release, not increased synthesis. [cite:Robbins 10e Ch 24]