Granulomatous & Chronic Inflammation
A Step 1–focused lesson on chronic and granulomatous inflammation: the macrophage/Th1 (IL-12→IFN-γ→TNF) mechanism, caseating vs. non-caseating differentials, giant-cell types, and buzzword vignettes for TB and sarcoidosis with explicit next-best-step decisions.
Chronic vs. granulomatous inflammation
Chronic inflammation is prolonged (weeks–months) inflammation in which active injury, tissue destruction, and repair (angiogenesis + fibrosis) occur simultaneously. The dominant cells are mononuclear: macrophages (the central player), lymphocytes (T and B), and plasma cells. Triggers: persistent infection (TB, viral hepatitis), prolonged toxin/foreign-material exposure (silica), and autoimmunity (RA).
Granulomatous inflammation is a distinctive pattern of chronic inflammation — a focal aggregate of activated macrophages that enlarge into epithelioid cells (abundant pink cytoplasm, elongated/vesicular nuclei), often fuse into multinucleated giant cells, and are rimmed by lymphocytes. Formation is Th1-driven: macrophages present antigen and secrete IL-12 → CD4⁺ Th1 cells release IFN-γ → activates macrophages into epithelioid/giant cells; macrophage-derived TNF maintains granuloma integrity. This mechanism explains why anti-TNF biologics (infliximab) can reactivate latent TB.
- Chronic inflammation cells: macrophages (central), lymphocytes, plasma cells (make antibody); eosinophils in parasitic/IgE-mediated disease
- Granuloma = epithelioid macrophages ± multinucleated giant cells, surrounded by a lymphocyte cuff
- Caseating (central necrosis) → TB and fungi (Histoplasma, Coccidioides, Blastomyces)
- Non-caseating (no necrosis) → sarcoidosis, Crohn disease, berylliosis, foreign body, primary biliary cholangitis
- Necrotizing but non-caseous → granulomatosis with polyangiitis (geographic necrosis, c-ANCA/anti-PR3), cat-scratch disease (stellate, central neutrophils)
- Th1 axis: IL-12 → IFN-γ → macrophage activation; TNF sustains the granuloma → screen PPD/IGRA before anti-TNF
- Sarcoid hypercalcemia: activated macrophages express 1α-hydroxylase → ↑ 1,25-(OH)₂ vitamin D
- Giant cells: Langhans (peripheral horseshoe nuclei, TB), foreign-body (haphazard nuclei), Touton (fat necrosis/xanthoma); Aschoff giant cell (rheumatic carditis)
Caseating vs. non-caseating granuloma
| Feature | Caseating | Non-caseating |
|---|---|---|
| Central necrosis | Present (cheesy, eosinophilic) | Absent |
| Classic causes | TB, fungi (Histo, Cocci, Blasto) | Sarcoidosis, Crohn, berylliosis, foreign body |
| Special stains | AFB (Ziehl-Neelsen), GMS/PAS for fungi | Stains negative for organisms |
| Buzzwords | Ghon complex, Langhans giant cells | Bilateral hilar LAD, ↑ACE, asteroid/Schaumann bodies |
| Next step | AFB smear + culture, NAAT | Dx of exclusion — rule out infection first |
A 44-year-old man who emigrated from India 8 months ago has 6 weeks of productive cough, drenching night sweats, weight loss, and hemoptysis. CXR shows a right-upper-lobe cavitary lesion. Biopsy: granulomas with central caseous necrosis ringed by giant cells whose nuclei line up peripherally in a horseshoe.
Diagnosis: Reactivation pulmonary tuberculosis (peripheral-nucleated cells = Langhans giant cells).
Next best step: Place the patient in airborne isolation, then confirm with acid-fast (Ziehl-Neelsen) stain + sputum culture / NAAT before starting RIPE therapy (rifampin, isoniazid, pyrazinamide, ethambutol). A granuloma alone is never enough — the organism must be documented.
A 34-year-old African-American woman has dyspnea and a dry cough, tender red shin nodules (erythema nodosum), and ankle arthralgia. CXR: bilateral hilar lymphadenopathy. Labs: hypercalcemia and elevated serum ACE. Transbronchial biopsy: non-caseating granulomas; giant cells contain star-shaped asteroid bodies.
Diagnosis: Sarcoidosis (the acute triad of erythema nodosum + hilar LAD + arthralgia/fever = Löfgren syndrome, good prognosis).
Next best step: Because sarcoid is a diagnosis of exclusion, order AFB + fungal stains/cultures on the biopsy to exclude TB/fungi first. Treat symptomatic disease (or hypercalcemia) with corticosteroids; the high calcium is from macrophage 1α-hydroxylase producing calcitriol — avoid vitamin D and sun exposure.
GRUELING captures the classic sarcoid picture:
- G — noncaseating Granulomas
- R — aRthralgia
- U — anterior Uveitis
- E — Erythema nodosum
- L — bilateral hilar Lymphadenopathy
- I — Interstitial fibrosis (restrictive PFTs, ↓DLCO)
- N — Negative PPD (cutaneous anergy) / Noncaseating
- G — hyperGammaglobulinemia (also ↑ACE, ↑Ca)
Bonus for giant cells: Langhans nuclei Line the periphery (horseshoe); foreign-body nuclei are thrown in haphazardly.
Multinucleated giant cells
| Giant cell | Nuclear pattern | Classic association |
|---|---|---|
| Langhans | Peripheral horseshoe/ring | TB (not specific) |
| Foreign body | Haphazard, random | Sutures, talc, prostheses |
| Touton | Central wreath of nuclei + foamy peripheral rim | Fat necrosis, xanthoma |
| Aschoff giant cell | Multinucleated; near Anitschkow "caterpillar-nuclei" cells | Rheumatic carditis (Aschoff body) |
- Before any anti-TNF agent (infliximab, adalimumab, etanercept): screen for latent TB (PPD/IGRA) + CXR → treat latent TB before the biologic
- Granuloma on biopsy → always add AFB + fungal stains/cultures before calling it sarcoidosis
- Bilateral hilar LAD + hypercalcemia + ↑ACE → sarcoidosis; confirm with biopsy showing non-caseating granulomas
- Sarcoid hypercalcemia / nephrolithiasis → corticosteroids; avoid supplemental vitamin D and sunlight
- Boy with recurrent catalase-positive infections (S. aureus, Serratia, Nocardia, Burkholderia, Aspergillus) → chronic granulomatous disease; test with DHR flow cytometry (or nitroblue tetrazolium) — defective NADPH oxidase
- Upper-lobe cavitary lesion + night sweats/weight loss → sputum AFB ×3 + NAAT and airborne isolation
Practice Pathology now
Board-style questions, spaced-repetition flashcards, and a Socratic AI tutor — free to start.