306.1 🎓 醫孞生版

306.1.0.1 📌 䞀頁重點

306.1.0.1.1 Hypersensitivity Pneumonitis (HP)
306.1.0.1.1.1 Definition
  • Immune-mediated ILD caused by inhalation of organic antigens
  • Type III + IV hypersensitivity reactions
  • Spectrum: acute → subacute → chronic (fibrotic)
  • 2020 ATS/JRS/ALAT updated classification: fibrotic vs non-fibrotic
306.1.0.1.1.2 Common Antigens
Disease Name Antigen Source
Farmer’s lung Thermophilic actinomycetes (Saccharopolyspora rectivirgula) Moldy hay
Bird fancier’s lung / pigeon breeder’s lung Avian proteins Pigeons, parakeets
Hot tub lung Mycobacterium avium complex Hot tub aerosols
Humidifier lung Thermophilic actinomycetes, fungi Contaminated humidifiers
Cheese washer’s lung Penicillium casei Mold
Mushroom worker’s lung Mushroom spores Compost
Bagassosis Thermoactinomyces sacchari Sugar cane bagasse
Suberosis Penicillium frequentans Cork
Maple bark stripper’s Cryptostroma corticale Maple bark
Isocyanate HP Isocyanates Paint, polyurethane
Metalworking fluid HP Mycobacterium immunogenum Metal cutting fluids
306.1.0.1.1.3 Clinical Presentation

Acute (4-12 hours post-exposure): - Fever, chills, malaise - Cough, dyspnea - Headache, myalgia - Diffuse crackles - Mimics flu / pneumonia - Resolves with antigen removal

Subacute (weeks-months): - Insidious onset - Progressive cough + dyspnea - Weight loss - Less prominent constitutional symptoms

Chronic / Fibrotic: - Progressive dyspnea + cough - Fibrosis (irreversible) - Honeycombing in severe - May mimic IPF - High mortality

306.1.0.1.1.4 Diagnosis

Antigen Exposure: - Critical for diagnosis - Detailed occupational + environmental history - Sometimes difficult to identify

HRCT: - Acute: ground-glass opacity, centrilobular nodules (poorly defined, often upper/mid lung) - Subacute: mosaic attenuation (air trapping + perfusion variation), ground-glass - Chronic: reticulation, traction bronchiectasis, honeycombing (mimics UIP); upper/mid lung predominance (vs IPF basilar)

Pulmonary Function Tests: - Restrictive pattern (acute) - Mixed obstructive-restrictive (chronic) - ↓ DLCO

Bronchoalveolar Lavage (BAL): - Lymphocytosis ≥ 30% (typical) - CD4/CD8 ratio < 1 (HP) — vs CD4/CD8 > 4 in sarcoidosis (key distinguisher) - Neutrophilia in fibrotic

Specific Antibodies: - Precipitins (serum IgG against antigens) - Helpful but not diagnostic alone - Positive in many exposed but asymptomatic

Inhalation Challenge: - Not routinely; only in specialized centers - Specific antigen exposure → symptoms + PFT decline

Lung Biopsy (Cryobiopsy / Surgical): - Granulomatous inflammation (non-fibrotic) - Bronchiolocentric inflammation - Multinucleated giant cells - Fibrosis pattern in chronic

306.1.0.1.1.5 Treatment

1. Antigen Avoidance (MOST IMPORTANT) - Identify + eliminate exposure - Occupational changes - Respirators / PPE - Environmental remediation

2. Corticosteroids - For acute / subacute / severe disease - Prednisone 0.5-1 mg/kg/d × 2-4 weeks → taper - Long-term low-dose if needed

3. Antifibrotic (Fibrotic HP) - Nintedanib (INPULSIS-HP, INBUILD trial subgroup) - Pirfenidone (some evidence) - For fibrotic HP with progression despite steroids - 2020 ATS guidelines incorporated

4. Immunosuppressants - Azathioprine, mycophenolate, rituximab - For refractory or progressive disease

5. Lung Transplantation - For end-stage fibrotic HP - Recurrence in transplant possible (antigen re-exposure)

306.1.0.1.2 Eosinophilic Pulmonary Disease
306.1.0.1.2.1 Categories
  • Idiopathic: acute eosinophilic pneumonia (AEP), chronic eosinophilic pneumonia (CEP), idiopathic hypereosinophilic syndrome (HES)
  • Infectious: parasitic (Loeffler, Strongyloides, Ascaris, Schistosoma), fungal (ABPA)
  • Drug-induced: many (NSAIDs, antibiotics, etc.)
  • Autoimmune: EGPA (Churg-Strauss), DRESS
  • Idiopathic + systemic: HES
306.1.0.1.2.2 Acute Eosinophilic Pneumonia (AEP)

Clinical: - Acute febrile illness (days) - Cough + dyspnea + pleuritic chest pain - Often in healthy adults - Smoking new initiation often trigger - Mimics community-acquired pneumonia - Can rapidly progress to respiratory failure

Diagnosis: - Diffuse infiltrates on CXR / HRCT - BAL eosinophils > 25% (often > 50%) - Peripheral eosinophilia often ABSENT at presentation (developing) - Exclude infections, drugs

Treatment: - Corticosteroids dramatic response (within days) - Prednisone 40-60 mg/d × 2-4 weeks - Complete resolution - No long-term issues - Avoid smoking restart

306.1.0.1.2.3 Chronic Eosinophilic Pneumonia (CEP)

Clinical: - Subacute (weeks-months) - Cough, dyspnea, weight loss, fever - More often women, age 40-60 - Asthma association (50%)

Diagnosis: - HRCT: peripheral, upper lobe predominant infiltrates (“photographic negative of pulmonary edema”) - Eosinophilia (peripheral + BAL) - Hypereosinophilia in blood

Treatment: - Corticosteroids dramatic response - Prednisone 20-40 mg/d - Often long-term low-dose - High relapse rate (50%) - Steroid-sparing: dupilumab, mepolizumab, benralizumab (emerging)

306.1.0.1.2.4 Allergic Bronchopulmonary Aspergillosis (ABPA)

Clinical: - Asthmatic or CF patients - Hypersensitivity to Aspergillus fumigatus - Wheezing, brown plugs, bronchiectasis

Diagnosis Criteria (Rosenberg-Patterson + ISHAM 2022 update): - Asthma or CF - Total IgE > 1000 IU/mL - Specific IgE to Aspergillus + serum precipitins - Pulmonary infiltrates - Central bronchiectasis (HRCT) - Eosinophilia

Treatment: - Oral corticosteroids (prednisone 0.5 mg/kg/d × 2 weeks → taper) - Itraconazole 200 mg BID × 4-6 months (reduces steroid use) - Voriconazole alternative - Dupilumab + mepolizumab for refractory (emerging) - Allergen-specific if identified

306.1.0.1.2.5 Eosinophilic Granulomatosis with Polyangiitis (EGPA / Churg-Strauss)
  • ANCA-associated vasculitis (Ch295)
  • Asthma + eosinophilia + vasculitis
  • Treatment: glucocorticoids + cyclophosphamide (severe) or rituximab; mepolizumab (2017 FDA — only biologic approved for EGPA)
306.1.0.1.2.6 DRESS Syndrome
  • Drug Reaction with Eosinophilia and Systemic Symptoms
  • Common drugs: anticonvulsants, allopurinol, sulfa, dapsone
  • Treatment: stop drug + steroids + supportive
306.1.0.1.2.7 Parasitic Eosinophilic Pneumonia
  • Strongyloides, Ascaris, Loeffler, Schistosoma
  • Travel history + stool studies + serology
  • Treatment: anti-parasitic
306.1.0.1.2.8 Idiopathic Hypereosinophilic Syndrome (HES)
  • Persistent eosinophilia > 1500/ÎŒL × 6 months
  • Organ involvement (heart, skin, GI, neuro)
  • FIP1L1-PDGFRA mutation (myeloid subtype)
  • Treatment: imatinib (myeloid), steroids, mepolizumab, ruxolitinib

306.1.0.2 🩺 床邊速查

  • HP: inhaled antigen → immune-mediated ILD; acute (4-12 h post-exposure), subacute, chronic (fibrotic)
  • HP HRCT: mosaic attenuation + ground-glass + centrilobular nodules; chronic → upper-mid lung fibrosis
  • HP BAL: lymphocytosis + CD4/CD8 < 1 (vs sarcoid > 4)
  • HP treatment: antigen avoidance + steroids + antifibrotic for fibrotic HP
  • AEP: acute + smoking trigger + BAL eos > 25%; dramatic response to steroids
  • CEP: subacute + asthma + “photographic negative of pulmonary edema”; relapse 50%
  • ABPA: asthma/CF + IgE > 1000 + central bronchiectasis; itraconazole + steroids + dupilumab for refractory