A 35-year-old woman presents with acute-onset severe thyroid pain, fever, and transient thyrotoxicosis followed by hypothyroidism. Thyroid biopsy shows granulomatous inflammation without germinal centers. Which clinical feature best distinguishes this condition from Hashimoto thyroiditis?

## Distinguishing Subacute (De Quervain) Thyroiditis from Hashimoto Thyroiditis ### Clinical Course Comparison | Phase | Subacute Thyroiditis | Hashimoto Thyroiditis | |-------|----------------------|----------------------| | **Phase 1** | Thyrotoxicosis (weeks 1–4) | Insidious hypothyroidism | | **Phase 2** | Euthyroid recovery (weeks 4–12) | Persistent hypothyroidism | | **Phase 3** | Hypothyroidism (rare, transient) | Lifelong hypothyroidism | | **Duration** | Self-limited (weeks to months) | Chronic, progressive | | **Autoantibodies** | Absent or low-titer | High-titer (TPO, thyroglobulin) | | **ESR/CRP** | Markedly elevated | Normal or mildly elevated | ### Pathological Features **Subacute (De Quervain) Thyroiditis:** - Granulomatous inflammation (non-caseating) - Absence of germinal centers - Likely viral etiology (mumps, measles, Coxsackievirus) - Transient destruction of follicles → thyroid hormone release → thyrotoxicosis - Recovery of follicular function → euthyroid phase - Rarely progresses to permanent hypothyroidism **Hashimoto Thyroiditis:** - Lymphocytic infiltration with germinal centers - Hürthle cell metaplasia - Autoimmune destruction (TPO and thyroglobulin antibodies) - Progressive hypothyroidism from onset - No initial thyrotoxic phase **Key Point:** The **triphasic course** (thyrotoxicosis → euthyroid → hypothyroidism) is pathognomonic for subacute thyroiditis and is the best clinical discriminator from Hashimoto. **High-Yield:** Subacute thyroiditis = painful, triphasic, self-limited, granulomas, NO autoantibodies. Hashimoto = painless, hypothyroid from start, autoimmune, germinal centers, HIGH autoantibodies. **Clinical Pearl:** In subacute thyroiditis, the thyrotoxicosis is due to **follicular destruction and hormone leakage**, not increased hormone synthesis (unlike Graves). TSH is suppressed in phase 1 but radioiodine uptake is LOW (distinguishes from Graves). **Mnemonic:** **DEQUERVAIN** = De Quervain's (subacute) = **D**estructive (follicles), **E**uthyroid recovery, **Q**uick onset, **U**sually viral, **E**levated ESR, **R**are hypothyroidism, **V**iral prodrome, **A**utoantibodies absent, **I**nflammatory (granulomatous), **N**o germinal centers. [cite:Harrison 21e Ch 405]