Granulomatous Diseases: High-Yield Pathology
A granuloma is a chronic inflammatory response characterized by a collection of activated epithelioid macrophages (often fused into multinucleated giant cells) surrounded by a rim of lymphocytes. Distinguishing between caseating and non-caseating granulomas is a classic board examination skill.
1. Caseating vs. Non-Caseating Granulomas
| Granuloma Type | Common Etiologies |
|---|---|
| Caseating | Tuberculosis (TB), Fungal infections (e.g., Histoplasmosis, Coccidioidomycosis). Characterized by central necrosis. |
| Non-Caseating | Sarcoidosis, Crohn disease, Berylliosis, Cat Scratch Disease (Stellate-shaped), Foreign body reaction. |
2. High-Yield Clinical Associations
- Sarcoidosis: Systemic disease featuring hilar lymphadenopathy, elevated ACE levels, and hypercalcemia (due to 1-alpha-hydroxylase activity in macrophages).
- Crohn’s disease: Transmural inflammation of the GI tract. Non-caseating granulomas are a pathognomonic finding (though only present in 30-50% of cases).
- Cat Scratch Disease: Caused by Bartonella henselae. Shows necrotizing granulomas with central debris, often described as “stellate” (star-shaped).
- Syphilis: Gummas (necrotizing granulomas) are seen in tertiary syphilis.
3. Pathological Exam Must-Knows
Pathology Pearl: Granuloma formation is a Type IV hypersensitivity reaction. Macrophages present antigen to CD4+ T-cells, which release Interferon-gamma (IFN-gamma). This cytokine activates the macrophages, promoting their transformation into epithelioid cells and multinucleated giant cells.
- Foreign Body Granuloma: Does not involve T-cell activation; caused by inert foreign material (e.g., sutures, talc).
- Giant Cells: Look for Langhans-type giant cells (nuclei arranged peripherally) in TB, versus Foreign body-type giant cells (nuclei scattered randomly) in foreign body reactions.