A 38-year-old woman presents with a 2-week history of severe neck pain, fever, and malaise. She reports a recent upper respiratory tract infection 3 weeks ago. On examination, the thyroid gland is tender, firm, and enlarged. Laboratory investigations show TSH 0.2 mIU/L (normal 0.5–5.0), free T4 8.5 ng/dL (normal 0.8–1.8), elevated ESR 68 mm/hr, and negative thyroid peroxidase (TPO) and thyroglobulin antibodies. Thyroid ultrasound shows heterogeneous echotexture with reduced vascularity. What is the most likely diagnosis?

Question

Accepted Answer

B. Subacute granulomatous thyroiditis. ## Clinical Diagnosis: Subacute Granulomatous Thyroiditis

### Key Clinical Features

**Key Point:** Subacute granulomatous thyroiditis (de Quervain's thyroiditis) is a viral-triggered, self-limited inflammatory disorder characterized by a triphasic course: thyrotoxicosis → euthyroidism → hypothyroidism.

### Diagnostic Criteria Met in This Case

| Feature | Finding | Significance |
|---------|---------|---------------|
| **Onset** | 3 weeks post-URI | Viral prodrome typical |
| **Neck pain** | Severe, tender thyroid | Hallmark feature |
| **Fever & malaise** | Present | Systemic inflammation |
| **TSH/T4 pattern** | Low TSH, high T4 | Phase 1: thyrotoxicosis |
| **Inflammatory markers** | Elevated ESR | Non-specific but marked elevation |
| **Antibodies** | Negative TPO, anti-Tg | Rules out autoimmune thyroiditis |
| **Ultrasound** | Heterogeneous, reduced flow | Consistent with granulomatous inflammation |

### Pathophysiology

1. **Viral trigger** → lymphocytic infiltration of thyroid
2. **Granuloma formation** → disruption of follicles
3. **Release of preformed thyroid hormone** → thyrotoxicosis (Phase 1)
4. **Recovery of follicular function** → euthyroidism (Phase 2)
5. **Transient hypothyroidism** → antibody-negative (Phase 3)

**High-Yield:** The **negative antibodies** are the key discriminator from Hashimoto's thyroiditis, which presents with positive TPO and anti-thyroglobulin antibodies.

### Clinical Pearl

**Clinical Pearl:** Unlike Graves' disease (which has sustained thyrotoxicosis and positive TSI), subacute thyroiditis shows **triphasic evolution** with self-resolution in 3–6 months. Radioiodine uptake is **suppressed** (unlike Graves', where it is elevated).

### Management

- **Mild cases:** NSAIDs (ibuprofen 400–600 mg TID)
- **Moderate-to-severe:** Corticosteroids (prednisone 40 mg daily, tapered over 6–8 weeks)
- **Beta-blockers:** For symptomatic thyrotoxicosis (propranolol 40–80 mg TID)
- **No antithyroid drugs** (PTU/methimazole) — thyroid hormone is being released, not synthesized

**Mnemonic:** **VIRAL** — **V**iral prodrome, **I**nflammatory markers elevated, **R**educed antibodies (negative), **A**cute neck pain, **L**imited course (self-resolving)

[cite:Robbins 10e Ch 24]

Answer

A. Acute suppurative thyroiditis

Answer

C. Hashimoto's thyroiditis

Answer

D. Riedel's thyroiditis

Explanation

Clinical Diagnosis: Subacute Granulomatous Thyroiditis

Key Clinical Features

Diagnostic Criteria Met in This Case

Pathophysiology

Clinical Pearl

Management

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Feature	Finding	Significance
Onset	3 weeks post-URI	Viral prodrome typical
Neck pain	Severe, tender thyroid	Hallmark feature
Fever & malaise	Present	Systemic inflammation
TSH/T4 pattern	Low TSH, high T4	Phase 1: thyrotoxicosis
Inflammatory markers	Elevated ESR	Non-specific but marked elevation
Antibodies	Negative TPO, anti-Tg	Rules out autoimmune thyroiditis
Ultrasound	Heterogeneous, reduced flow	Consistent with granulomatous inflammation