Which histopathological feature best distinguishes acute suppurative thyroiditis from subacute granulomatous thyroiditis?

Explanation

## Distinguishing Acute Suppurative from Subacute Granulomatous Thyroiditis ### Acute Suppurative Thyroiditis **Key Point:** Acute suppurative thyroiditis is characterized by **acute purulent inflammation** with neutrophilic infiltration and abscess formation, typically caused by bacterial infection (often secondary to hematogenous spread or direct inoculation). **Histology:** - Dense neutrophilic infiltration - Microabscess formation - Suppuration and tissue necrosis - Minimal granulomatous response ### Subacute Granulomatous Thyroiditis (De Quervain's) **Key Point:** Subacute granulomatous thyroiditis shows **granulomatous inflammation** with epithelioid histiocytes and multinucleated giant cells, typically viral in etiology (mumps, measles, EBV). **Histology:** - Granulomatous infiltration (epithelioid cells + giant cells) - Follicular destruction - Minimal neutrophils - Fibrosis in later stages ### Comparison Table | Feature | Acute Suppurative | Subacute Granulomatous | | --- | --- | --- | | **Primary infiltrate** | Neutrophils (PMNs) | Epithelioid cells + giant cells | | **Abscess formation** | Yes, prominent | No | | **Granulomas** | Absent | Present | | **Etiology** | Bacterial | Viral | | **ESR** | Moderate elevation | Very high (>50) | | **TSH suppression** | Variable | Marked | **High-Yield:** The **presence of neutrophilic microabscesses** is the pathognomonic discriminator of acute suppurative thyroiditis, whereas **granulomatous inflammation with giant cells** defines subacute granulomatous thyroiditis. **Clinical Pearl:** Acute suppurative thyroiditis is rare in the modern era due to antibiotic use; it typically occurs in immunocompromised patients or after thyroid procedures. Subacute granulomatous thyroiditis is more common and often follows viral upper respiratory tract infection.