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Acute Exacerbation of Interstitial Lung Disease (AE-ILD)

Comprehensive Answer for MD Examinations (15 Marks)

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1. Definition

1. Previous or concurrent diagnosis of ILD
2. Acute worsening or new onset of dyspnea, typically within 30 days or less
3. HRCT showing new bilateral ground-glass opacities and/or consolidation superimposed on a background pattern consistent with the pre-existing ILD (e.g., UIP)
4. Deterioration not fully explained by cardiac failure or fluid overload

Key update from 2016 revision: the definition now includes exacerbations with an identifiable trigger (infections, aspiration, drugs, surgery) - not just idiopathic events as in the older 2007 definition.

• Murray & Nadel's Textbook of Respiratory Medicine, p. 2027
• Harrison's Principles of Internal Medicine 22E, p. 2308
• León-Román F et al., Medicina 2025 [PMID: 41470099]

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2. Epidemiology and Incidence

• AE is most common and most severe in IPF, but can occur in any fibrotic ILD including:
  • Connective tissue disease-associated ILD (CTD-ILD)
  • Hypersensitivity pneumonitis (fibrotic HP)
  • NSIP
  • Progressive pulmonary fibrosis (PPF) - 1-year incidence 12.5%, 5-year 38% (Kim et al. 2024 [PMID: 39593055])
• Fishman's Pulmonary Diseases & Disorders, p. 953

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3. Etiology and Triggers

A. Idiopathic (no identifiable trigger found)

• Most common scenario in IPF

B. Triggered / Secondary

Regardless of trigger, the pathophysiology and outcomes are similar, which is why the 2016 definition includes all triggers under one umbrella.

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4. Pathogenesis

1. Disordered epithelial cell integrity - pre-existing alveolar epithelial dysfunction in fibrotic ILD makes tissue susceptible to secondary insults
2. Acute inflammation - surge in neutrophils, cytokines (TNF-α, IL-1β, IL-6, IL-8)
3. Excess matrix metalloproteinases (MMPs) - break down alveolar basement membrane
4. Antifibrinolytic alveolar milieu - promotes fibrin deposition
5. Occult viral infection - may act as a "second hit" on already remodeled tissue
6. Microbiome dysbiosis - higher total microbial load and altered community (Campylobacter, Stenotrophomonas) found in BAL of AE-IPF patients

• Murray & Nadel, p. 2027
• Fishman's, p. 953

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5. Histopathology

• Diffuse alveolar septal thickening in a pale eosinophilic matrix
• Hyaline membranes - pathognomonic of DAD
• Fibrin deposition in alveolar spaces
• Type II pneumocyte hyperplasia
• Superimposed organizing pneumonia (OP pattern) can also occur
• Underlying UIP features: fibroblastic foci, honeycombing, temporal heterogeneity
• Histologic examination is NOT required for diagnosis - used when biopsy/autopsy is performed

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6. Clinical Features

Symptoms

• Abrupt onset of progressive dyspnea (over days to weeks, <30 days)
• Worsening hypoxemia - may rapidly progress to respiratory failure
• Dry cough, fatigue
• Often no fever (fever suggests infectious trigger)
• Preceding period of relative stability in known ILD patient

Signs

• Bilateral fine crackles ("velcro crackles") - pre-existing
• Cyanosis, tachypnea, accessory muscle use
• Reduced breath sounds
• Signs of right heart failure if severe/chronic
• No clinical feature is specific - diagnosis rests on exclusion + imaging

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7. Investigations

A. Blood Tests

B. HRCT Chest (Most Important Investigation)

• New bilateral ground-glass opacities (GGOs) and/or consolidation superimposed on pre-existing UIP pattern
• Background reticular pattern, traction bronchiectasis, honeycombing - features of underlying IPF
• Distribution: diffuse, peripheral, or bilateral patchy
• Absence of pleural effusion, cardiac enlargement (argues against cardiogenic cause)
• 3 radiologic subtypes described by Akira et al.:
  • Type 1 (peripheral) - GGO superimposed on UIP; better prognosis
  • Type 2 (multifocal) - bilateral patchy GGO
  • Type 3 (diffuse) - diffuse GGO; worst prognosis

C. Bronchoalveolar Lavage (BAL)

• Useful to exclude infection (bacteria, fungi, PCP, CMV, Pneumocystis)
• AE-IPF BAL typically: increased neutrophils, eosinophils
• Increased total microbial burden in AE-IPF
• Carries procedural risk - may worsen hypoxemia; risk-benefit must be weighed

D. Pulmonary Function Tests

• Restrictive pattern (FVC ↓, TLC ↓, DLCO ↓)
• Acute decline in FVC or DLCO compared to baseline
• Not routinely performed during acute phase

E. Echocardiogram

• To exclude left heart failure as alternative or contributing cause

F. Lung Biopsy

• Generally not recommended during acute phase (high procedural risk, mortality)
• If performed: shows DAD ± OP on UIP background

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8. Diagnosis

1. Prior or concurrent ILD diagnosis
2. Dyspnea acutely worsening within <30 days
3. HRCT: new bilateral GGO/consolidation superimposed on fibrotic background
4. Not explained by cardiac failure or fluid overload

• Cardiogenic pulmonary edema
• Pneumothorax
• Pulmonary embolism
• Infectious pneumonia (viral, bacterial, fungal - especially Pneumocystis)
• Drug-induced pneumonitis
• Malignancy

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9. Management

Guiding Principle

A. Respiratory Support (Cornerstone)

Important: Mechanical ventilation in AE-ILD carries very high mortality and is NOT recommended unless as a bridge to lung transplantation.

B. Corticosteroids

• Mainstay of pharmacological treatment despite absence of RCT evidence
• Rationale: suppress acute alveolar inflammation and cytokine surge
• Regimen (commonly used):
  • Methylprednisolone pulse: 0.5-1 g/day IV for 3 days
  • Followed by high-dose oral prednisolone: 1 mg/kg/day tapering over weeks-months
• International expert survey: majority of pulmonologists administer steroids
• Evidence base: observational studies only; retrospective studies have significant bias
• Murray & Nadel, p. 2027; Fishman's, p. 953

C. Antifibrotic Agents

• Nintedanib and pirfenidone: May reduce the rate of acute exacerbations in stable IPF (disease-modifying)
• Role during an active AE-ILD: controversial; expert consensus suggests initiating or continuing antifibrotic therapy
• INBUILD trial (2022): nintedanib slows progression in multiple fibrotic ILDs (non-IPF PPF) - reduces annual FVC decline [PMID: 34475231]
• Real-world meta-analysis (2024): pirfenidone and nintedanib have comparable efficacy and safety in IPF [PMID: 38963453]

D. Antibiotics

• Broad-spectrum antibiotics given empirically in most patients
• Rationale: infection is the most common identifiable trigger; often cannot be excluded clinically
• Cover community-acquired and hospital-acquired pathogens
• Add antifungal/anti-PCP (trimethoprim-sulfamethoxazole) if clinically indicated or immunosuppressed

E. Additional / Investigational Treatments

F. Supportive Care

• VTE prophylaxis (DVT prophylaxis)
• Careful fluid management - avoid fluid overload; may worsen alveolar flooding
• Treat concomitant pulmonary hypertension
• Nutritional support
• Palliative care consultation early - median survival 2-4 months despite treatment
• Goals of care discussion with patient and family (high mortality)

G. Lung Transplantation

• The only treatment that may improve survival in end-stage ILD with AE
• AE-ILD during transplant evaluation may lead to emergency listing
• Outcome depends on urgency, overall condition, and center experience
• Mechanical ventilation/ECMO as bridge to transplant

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10. Prognosis

• Diffuse (Type 3) CT pattern
• Severe baseline hypoxemia (PaO2/FiO2 < 200)
• Need for mechanical ventilation
• Older age, lower FVC/DLCO at baseline
• Raised LDH, KL-6

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11. Prevention

• Antifibrotic therapy (nintedanib, pirfenidone): reduces AE incidence in IPF
• Anti-reflux surgery: laparoscopic antireflux surgery in IPF patients with abnormal acid GER lowered AE rate, respiratory hospitalization, and death (Murray & Nadel, p. 2026)
• Annual influenza and pneumococcal vaccination
• Avoid unnecessary bronchoscopy/surgical lung biopsy in advanced ILD
• Caution with drugs known to trigger AE (leflunomide, chemotherapy)

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12. AE-ILD vs AE-IPF: Scope Expansion

• Luppi F et al., Nat Rev Rheumatol 2022 [PMID: 34876670]
• Kim MJ et al., Respir Res 2024 [PMID: 39593055]

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13. Exam High-Yield Points Summary

1. Definition: Acute worsening <30 days + new bilateral GGO on HRCT + exclude cardiac failure, in known ILD patient
2. 2016 updated definition: Includes triggered (infection, surgery) AND idiopathic events
3. Histology: DAD superimposed on UIP
4. Incidence: 5-15%/year in IPF; Mortality >50% in-hospital
5. Investigation of choice: HRCT chest
6. Biomarkers: KL-6, SP-D elevated
7. Management: No RCTs; high-dose steroids (methylprednisolone pulse 0.5-1 g/day) + supportive O2 therapy
8. Mechanical ventilation: Controversial; only as bridge to transplant
9. Prognosis: Median survival 2-4 months
10. Prevention: Antifibrotics reduce AE incidence; anti-reflux therapy beneficial

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References

• Murray & Nadel's Textbook of Respiratory Medicine (7e), Section on Acute Exacerbations of IPF, p. 2027
• Fishman's Pulmonary Diseases and Disorders (6e), Acute Exacerbations section, p. 953
• Harrison's Principles of Internal Medicine (22e, 2025), Acute Exacerbations of IIPs, p. 2308
• Collard HR et al. Acute Exacerbations of Idiopathic Pulmonary Fibrosis - International Working Group Report. Am J Respir Crit Care Med 2016 [current diagnostic standard]
• León-Román F et al. Acute Exacerbation of ILD: Early Diagnosis and Treatment. Medicina 2025 [PMID: 41470099]
• Kim MJ et al. Acute exacerbation of progressive pulmonary fibrosis: incidence and outcomes. Respir Res 2024 [PMID: 39593055]
• Luppi F et al. Acute exacerbation of ILD associated with rheumatic disease. Nat Rev Rheumatol 2022 [PMID: 34876670]
• Dhanani Z, Gupta R. Management of ILD in the ICU. J Clin Med 2024 [PMID: 39597801]
• Flaherty KR et al. (INBUILD trial). Nintedanib in progressive ILDs. Eur Respir J 2022 [PMID: 34475231]