ACUTE EXACERBATION OF INTERSTITIAL LUNG DISEASE (AE-ILD)

1. Definition

Acute Exacerbation of ILD (AE-ILD)

An acute, clinically significant deterioration in respiratory status, characterized by new widespread alveolar damage, occurring in a patient with pre-existing ILD, with or without an identifiable trigger, and not fully explained by cardiac failure or fluid overload.

Classic Definition 

An unexplained worsening of dyspnea within < 30 days, associated with:

• New bilateral ground-glass opacities (± consolidation) on HRCT
• On a background of established ILD
• Exclusion of alternative causes

2. Classification

A. Based on Etiology

B. Based on Underlying ILD

• AE-IPF (most studied, worst prognosis)
• AE-CTD-ILD (RA-ILD, SSc-ILD, MCTD)
• AE-Hypersensitivity pneumonitis
• AE-Sarcoidosis (rare)
• AE-Drug-induced ILD
• AE-Post-COVID fibrotic ILD

3. Pathophysiology 

Central Event

➡️ Diffuse Alveolar Damage (DAD) superimposed on fibrotic lung

Pathogenic Cascade

1. Trigger or spontaneous epithelial injury
2. Loss of alveolar epithelial integrity
3. Excessive innate immune activation
4. Cytokine surge:
• IL-6, IL-8, TNF-α
• TGF-β (fibrogenesis)

5. Endothelial injury → capillary leak
6. Hyaline membrane formation
7. Acute lung injury pattern identical to ARDS

Why AE-ILD is Worse Than ARDS

• Non-compliant fibrotic lung
• Reduced recruitability
• Extreme V/Q mismatch
• High risk of VILI even with low pressures

4. Common Triggers

## Up to 50% are idiopathic

5. Clinical Presentation

Symptoms

• Rapidly progressive dyspnea (hours–days)
• Dry cough
• Severe hypoxemia
• Fever may or may not be present

Signs

• Tachypnea
• Fine inspiratory crackles
• Accessory muscle use
• Cyanosis
• Signs of respiratory failure

6. Diagnostic Criteria 

All must be present:

1. Known ILD
2. Acute worsening of dyspnea (<1 month)
3. New bilateral GGOs ± consolidation on HRCT
4. Not explained by:
• Heart failure
• Fluid overload
• Pulmonary embolism

7. Differential Diagnosis 

8. Investigations

A. Blood Tests

• CBC (infection, anemia)
• CRP, Procalcitonin
• ABG → severe hypoxemia, respiratory alkalosis
• LDH ↑ (marker of lung injury)
• Autoimmune panel (if undiagnosed ILD)

B. Imaging

HRCT CHEST – GOLD STANDARD

Typical Patterns

Background UIP features:

• Honeycombing
• Reticulation
• Traction bronchiectasis

C. Bronchoscopy / BAL

 NOT routinely recommended

• High risk of deterioration
• Consider only if infection strongly suspected and patient stable

10. Management (NO PROVEN CURATIVE THERAPY)

Principles

• Supportive care
• Treat triggers
• Minimize ventilator-induced lung injury
• Early goals-of-care discussion

11. Oxygen & Ventilatory Support

A. Oxygen Therapy

• Target SpO₂ 88–92%
• Avoid hyperoxia (oxidative injury)

B. HFNC

 Preferred initial support

• Improves comfort
• Reduces work of breathing
• Avoids intubation in some patients

C. Non-Invasive Ventilation (NIV)

 Use cautiously

• Short trial only
• Failure rate high
• Avoid prolonged NIV → delayed intubation

D. Invasive Mechanical Ventilation

 Very poor prognosis

Ventilation Strategy (ARDS-LIKE BUT EVEN MORE CONSERVATIVE)

## Many guidelines discourage IMV unless bridge to transplant

12. Pharmacological Therapy

A. Corticosteroids (Mainstay despite weak evidence)

Common Regimens

• Methylprednisolone Then prednisolone 
• Slow taper over weeks

 Evidence: observational, no RCT mortality benefit

B. Antibiotics

• Empiric broad-spectrum
• Cover atypicals + PJP if immunosuppressed

C. Immunosuppressants (CONTROVERSIAL)

 Avoid routine use in AE-IPF

D. Antifibrotics

• Nintedanib / Pirfenidone
• Not useful acutely
• ✔ May reduce future AE risk

E. ECMO

• Only as bridge to lung transplantation
• Not recommended as destination therapy

13. Fluid & ICU Care

• Conservative fluid strategy
• Avoid fluid overload
• Early nutrition
• DVT prophylaxis
• Stress ulcer prophylaxis

14. Prognosis

Mortality Rates

15. AE-ILD vs ARDS 

16. Prevention

• Vaccination
• Early treatment of infections
• Avoid high FiO₂
• Avoid unnecessary surgery
• Lung-protective ventilation always
• Antifibrotics in stable disease

17. End-of-Life Care

• Early palliative care involvement
• Discuss goals of care early
• Avoid futile escalation