## Non-Caseating vs. Caseating Granulomas **Key Point:** **Sarcoidosis** is the prototypical cause of non-caseating granulomatous inflammation. The absence of central caseous necrosis is a hallmark feature that helps distinguish it from tuberculosis. ### Classification of Granulomatous Diseases | Disease | Necrosis Type | Key Features | |---------|---------------|---------------| | **Sarcoidosis** | Non-caseating | Idiopathic; multisystem; elevated ACE; hypercalcemia | | **Tuberculosis** | Caseating | Acid-fast bacilli; Ghon focus; cavitary lesions | | **Leprosy** | Caseating (variable) | Acid-fast bacilli; skin/nerve involvement | | **Fungal infections** | Caseating | Fungal elements visible on special stains | | **Berylliosis** | Non-caseating | Occupational exposure to beryllium | | **Crohn's disease** | Non-caseating | GI tract; skip lesions; fissuring ulcers | **High-Yield:** The **presence of caseous necrosis** suggests an infectious etiology (TB, fungal, leprosy); **absence of caseous necrosis** suggests a non-infectious cause (sarcoidosis, Crohn's, berylliosis). ### Sarcoidosis — Clinical Clues - Multisystem involvement (lungs, skin, eyes, heart, CNS) - Elevated serum ACE (angiotensin-converting enzyme) - Hypercalcemia and hypercalciuria - Diagnosis of exclusion (must rule out TB, fungal, Crohn's) **Clinical Pearl:** When you see "non-caseating granuloma" on a biopsy, think **sarcoidosis first**, but always exclude infection (especially TB) with appropriate cultures and stains before confirming idiopathic sarcoidosis.
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