Pathology

Pathology/C/25

Granulomatous diseases of the lung

肺の肉芽腫性疾患

タグ
High-yield / ポイント

Granuloma — Recap

  • Granulomatous inflammation: special form of chronic inflammation = aggregates of activated macrophages with scattered lymphocytes
  • Composition: central necrosis + epithelioid cells (modified macrophages) + giant cells (fused epithelioid cells) + lymphocytes + fibroblasts
  • Morphology (H&E): epithelioid cells (pink granular cytoplasm, indistinct borders); surrounded by lymphocyte collar; older granulomas surrounded by fibroblasts/CT; Langhans/multinucleated giant cells (40–50 µm; fusions of activated macrophages)

A) Tuberculosis

Causative agents

  • Mycobacterium tuberculosis (mostly), M. bovis, M. africanum
  • Transmitted by respiratory droplets

Clinical forms

Primary tuberculosis:

  • Caseating granuloma (tubercle): caseous necrosis in center; epithelioid cells; rimmed by fibroblasts, lymphocytes, histiocytes; occasionally Langhans giant cells
  • Lung lesion spreads to lymph nodes → Ranke-Ghon complex:
    • Tuberculoma (parenchymal lesion) → lymphangitis → lymphadenitis

Secondary (reactivated) tuberculosis:

  • Immunocompromised patients
  • Affects upper lobe + apex of lung
  • Symptoms: fever, hemoptysis, night sweats, chest pain, malaise

Systemic (Miliary) tuberculosis:

  • Extra-pulmonary hematogenous dissemination → bacteria spread through lymphatics + bloodstream → multiple organ involvement

Diagnosis

  • Acid-fast (Ziehl-Neelsen) staining, PCR, or culture
  • Mycobacteria stain red; background stains blue

B) Sarcoidosis

  • Multisystemic disease of unknown origin; involves lungs in 90% of cases
  • Presents as bilateral hilar lymphadenopathy

Morphology

  • Non-caseating epithelioid cell granulomas (non-infective)
  • Giant cells with Asteroid body + Schaumann body

Other manifestations

  • Skin: erythema nodosum, lupus pernio, subcutaneous nodules
  • Eyes: dry eyes, blurry vision
  • Lymph nodes: enlarged
  • Heart: complications
  • Liver and spleen: enlargement
  • Joints: pain, arthritis

Diagnosis & Treatment

  • Diagnosis of exclusion: culture + special stains (acid-fast) are negative
  • Treatment: steroids for severe symptoms

C) Wegener Granulomatosis (Granulomatosis with Polyangiitis)

Necrotizing vasculitis characterized by a classic triad:

  1. Acute necrotizing granulomas of the upper and lower respiratory tract
  2. Necrotizing vasculitis of small- and medium-sized vessels
  3. Focal/diffuse necrotizing glomerulonephritis (renal vasculitis)

Pathogenesis

  • Cell-mediated hypersensitivity to inhaled infectious or environmental agent
  • c-ANCAs present in most cases

Clinical features

  • Chronic sinusitis, mucosal ulceration of nasopharynx
  • Glomerulonephritis
  • Treatment: steroids

💡 High-yield: TB = caseating granuloma; Langhans giant cells; Ranke-Ghon complex; acid-fast (Ziehl-Neelsen) staining. Sarcoidosis = non-caseating granulomas; bilateral hilar LAD; Asteroid + Schaumann bodies; diagnosis of exclusion. Wegener = triad: necrotizing granulomas + vasculitis + glomerulonephritis; c-ANCA+.