A 35-year-old woman presents with acute onset severe thyroid pain, fever, and dysphagia following an upper respiratory tract infection. Laboratory investigations show elevated ESR, normal thyroid function tests, and a low radioiodine uptake on thyroid scan. All of the following are characteristic features of acute suppurative thyroiditis EXCEPT:

Explanation

## Acute Suppurative Thyroiditis: Key Distinguishing Features ### Pathophysiology Acute suppurative thyroiditis is a rare bacterial infection of the thyroid gland, usually following an upper respiratory tract infection or bacteremia. The thyroid's rich blood supply and lymphatic drainage make it susceptible to seeding of pathogens. ### Clinical Presentation **Key Point:** Acute suppurative thyroiditis presents with acute onset severe thyroid pain, fever, dysphagia, and systemic signs of infection — NOT with hyperthyroidism or thyroid dysfunction. ### Laboratory & Imaging Findings | Feature | Acute Suppurative Thyroiditis | |---------|------------------------------| | **Thyroid Function Tests** | Normal or mildly elevated free T4 (from tissue destruction, not synthesis) | | **TSH** | Normal or slightly suppressed | | **Radioiodine Uptake** | Low (suppressed by inflammation, not by hyperthyroidism) | | **ESR/CRP** | Markedly elevated | | **Ultrasound** | Focal or diffuse hypoechoic areas, abscess formation | **High-Yield:** The key distinction is that thyroid function tests remain **normal or only mildly deranged** because the gland is infected, not hyperactive. Unlike thyroiditis with thyrotoxicosis (subacute, postpartum), there is no true thyroid hormone excess. ### Causative Organisms - **Most common:** Staphylococcus aureus, Streptococcus pyogenes - **Less common:** Gram-negative organisms, anaerobes - **Source:** Hematogenous spread, direct extension from adjacent structures, or seeding via pyriform sinus fistula ### Predisposing Factors **Clinical Pearl:** Pyriform sinus fistula (remnant of pharyngeal pouch) is a common anatomical predisposing factor, especially in recurrent or left-sided suppurative thyroiditis. ### Why Option 3 is Incorrect Option 3 states "Thyroid function tests are typically elevated with suppressed TSH" — this describes **thyrotoxicosis** (as seen in subacute thyroiditis with hormone release), NOT acute suppurative thyroiditis. In suppurative thyroiditis, thyroid function remains normal because the gland is infected, not hyperactive. The low radioiodine uptake reflects inflammation and suppression, not increased hormone synthesis. ## Differential: Thyroiditis Subtypes ```mermaid flowchart TD A[Thyroiditis]:::outcome --> B{Presentation?}:::decision B -->|Acute pain + fever + toxicity| C[Suppurative Thyroiditis]:::outcome B -->|Subacute pain + thyrotoxicosis| D[Subacute Thyroiditis]:::outcome B -->|Painless + postpartum| E[Postpartum Thyroiditis]:::outcome B -->|Painless + firm gland| F[Autoimmune Thyroiditis]:::outcome C --> G[TFTs normal, Low uptake]:::action D --> H[TFTs elevated, Low uptake]:::action E --> I[TFTs elevated early, then low]:::action F --> J[TFTs low, High TPO antibodies]:::action ``` **Key Point:** The **absence of thyroid hormone excess** (normal TFTs, normal/suppressed TSH) is the defining laboratory feature that distinguishes suppurative thyroiditis from other forms of thyroiditis with thyrotoxicosis.