Idiopathic Pulmonary Fibrosis (IPF) with Acute Exacerbation - Full Details for MD Examination

1. DEFINITION

2. EPIDEMIOLOGY

• Incidence and prevalence increase markedly with age, particularly after 75 years
• Worldwide IPF mortality has increased steadily

3. ETIOPATHOGENESIS

Risk Factors

• Cigarette smoking - strongest environmental risk factor
• Age >60 years
• Male sex
• Gastroesophageal reflux disease (GERD) - microaspiration hypothesis
• Viral infections (herpesvirus, EBV, CMV)
• Occupational dust exposure (metal, wood dust)

Genetic / Familial IPF

• Familial pulmonary fibrosis (FPF): identified in ~15% as familial clusters
• Gene mutations: SFTPC (surfactant protein C), SFTPA2 (surfactant protein A2), MUC5B (mucin 5B)
• ~15% of FPF cases: short telomere syndrome from mutations in TERC, TERT (telomerase components) - may present with bone marrow failure, premature graying, cirrhosis, nail dystrophy, mucosal leukoplakia

Pathogenesis (Current Model)

1. Epithelial injury - repeated microinjuries to alveolar epithelial cells (type II pneumocytes)
2. Abnormal wound healing - failure of normal regeneration
3. Fibroblast activation - myofibroblast proliferation and collagen deposition
4. Fibroblast foci formation - subepithelial collections of myofibroblasts; hallmark of active fibrogenesis
5. Progressive architectural destruction - honeycombing, traction bronchiectasis

4. HISTOPATHOLOGY - UIP PATTERN

• Temporal and spatial heterogeneity - areas of dense fibrosis alternating with normal lung
• Subpleural and paraseptal distribution - lower lobe predominance
• Fibroblast foci - discrete subepithelial collections of myofibroblasts and collagen (marker of active fibrogenesis)
• Honeycombing - enlarged cystic airspaces lined by bronchiolar epithelium, often mucin-filled
• Minimal inflammation
• Gross appearance: nodular pleural surface resembling hepatic cirrhosis ("cobblestone" or "shaggy" appearance)

Histopathology of ILD. Panel A (top left): UIP/IPF - spatial heterogeneity with fibroblast foci (inset). Harrison's 22E, Fig. 304-3

5. CLINICAL FEATURES

Symptoms

• Slowly progressive dyspnea - over months to years (insidious onset)
• Non-productive cough (dry, persistent)
• Rare systemic or extrapulmonary symptoms
• Constitutional symptoms (fatigue, weight loss) may occur with advanced disease

Signs

• Bibasilar fine, dry (Velcro) inspiratory crackles - most characteristic
• Digital clubbing - 45-75% of patients
• Features of cor pulmonale in advanced disease (elevated JVP, right heart failure, peripheral edema)
• Cyanosis in late disease

6. INVESTIGATIONS

Pulmonary Function Tests (PFTs)

• Restrictive ventilatory defect: reduced TLC, FVC, FEV1 (with preserved or elevated FEV1/FVC ratio)
• Reduced DLCO (diffusing capacity for CO) - often disproportionately low; correlates with prognosis
• Progressive FVC decline >10% per year = marker of disease progression and poor prognosis

6-Minute Walk Test (6MWT)

• Reduced exercise tolerance
• Desaturation during exercise (SpO2 <88%) is common
• Used for transplant listing criteria

Chest HRCT (High-Resolution CT) - MANDATORY

• Bilateral, symmetric, subpleural, basilar-predominant reticulation
• Honeycombing ± traction bronchiectasis
• Geographic or heterogeneous involvement
• No features suggesting an alternative diagnosis

• Extensive ground-glass opacities
• Upper or mid-lung predominance
• Micronodules
• Bronchovascular distribution
• Mosaic attenuation

HRCT patterns in ILD. A: IPF with classic UIP pattern (subpleural reticulation, honeycombing). Harrison's 22E, Fig. 304-2

Blood/Serological Tests

• ANA, rheumatoid factor, anti-CCP: to exclude connective tissue disease (CTD)
• Hypersensitivity precipitins: to exclude hypersensitivity pneumonitis (HP)
• CBC, metabolic panel: baseline and comorbidity assessment
• ABG: hypoxemia (type 1 respiratory failure) at rest or exercise

Bronchoalveolar Lavage (BAL)

• Used to exclude other diagnoses (infection, malignancy, eosinophilia)
• BAL cell differential in IPF: may show slightly elevated neutrophils/eosinophils
• Not diagnostic for IPF

Lung Biopsy

• VATS (Video-Assisted Thoracoscopic Surgery) lung biopsy is preferred if biopsy is needed
• Transbronchial biopsy (TBBx) is diagnostic in <1/3 of cases - not preferred
• Cryobiopsy is an emerging alternative
• Biopsy needed if HRCT pattern is not "definite UIP" in appropriate clinical context

7. DIAGNOSIS OF IPF

1. Exclusion of all other causes of fibrosing lung disease - CTD, hypersensitivity pneumonitis, drug toxicity, sarcoidosis
2. Either:
   • A definite UIP pattern on HRCT (sufficient without biopsy in the right clinical context), OR
   • A UIP pattern on surgical lung biopsy (when HRCT is indeterminate)
3. Multidisciplinary discussion (MDD) among pulmonology, radiology, and pathology specialists with ILD expertise increases diagnostic accuracy

8. TREATMENT OF IPF (Stable Disease)

Disease-Modifying (Antifibrotic) Therapy

What NOT to Use

• Prednisone + azathioprine + NAC: PANTHER-IPF trial showed increased mortality and hospitalization - now contraindicated
• Interferon-γ: INSPIRE trial - no survival benefit
• Warfarin: no benefit, potential harm

Supportive / Adjunctive Care

• Supplemental oxygen (when SpO2 <88% at rest or exercise) - reduces pulmonary hypertension risk
• Pulmonary rehabilitation - improves exercise tolerance
• PPI / antacid therapy for GERD (weak recommendation; data mixed)
• Pneumococcal and influenza vaccination
• Treatment of comorbidities (pulmonary hypertension, OSA, lung cancer, DVT/PE)
• Palliative care for dyspnea (opioids, benzodiazepines)

Lung Transplantation

• Indicated for: significant FVC decline, oxygen dependence, FVC <80% predicted, DLCO <40% predicted
• ISHLT criteria for referral; bilateral lung transplant preferred
• Extends survival and improves quality of life in selected patients

9. ACUTE EXACERBATION OF IPF (AE-IPF)

Definition (International Working Group Report, 2016)

"An acute clinically significant respiratory deterioration characterized by evidence of new widespread alveolar abnormality"

Diagnostic Criteria (All 4 must be met)

1. Previous or concurrent diagnosis of IPF
2. Acute worsening or development of dyspnea - typically <1 month duration
3. CT findings: new bilateral ground-glass opacity and/or consolidation superimposed on a background UIP pattern
4. Deterioration not fully explained by cardiac failure or fluid overload

Classification

• AE-IPF with identifiable trigger: respiratory infection (bacterial/viral), aspiration, drug toxicity, surgical procedure (esp. post-lung resection)
• AE-IPF without identifiable trigger (idiopathic AE-IPF): many acute episodes have no identified cause

Epidemiology

• Annual incidence: 4-15% of IPF patients
• Mortality: >50% in-hospital mortality; 1-year mortality approaches 90% in some series
• Some deaths in IPF are directly attributed to acute exacerbation episodes

Pathogenesis of AE-IPF

• Exact mechanism unclear
• Proposed triggers/mechanisms:
  • Occult viral infection (herpesvirus family)
  • Microaspiration
  • Disordered epithelial cell integrity
  • Acute inflammation with excessive cytokines and matrix metalloproteinases (MMPs)
  • Antifibrinolytic alveolar environment
  • Surgical stress or anesthesia

Histopathology of AE-IPF

• Diffuse alveolar damage (DAD) superimposed on background UIP - most common pattern
• Occasionally: organizing pneumonia pattern, extensive fibroblastic foci
• Histologic evaluation is not required to diagnose AE-IPF, but biopsy/autopsy will show the above

Clinical Features

• Rapid (<1 month) worsening of dyspnea
• Worsening hypoxemia (progressive desaturation, increasing oxygen requirements)
• New bilateral crackles on new areas of the lung
• Fever may or may not be present (fever more suggestive of infection)
• Tachycardia, tachypnea

HRCT Findings in AE-IPF

• New bilateral ground-glass opacities and/or consolidation
• Superimposed on the background UIP pattern (honeycombing + subpleural reticulation)
• Diffuse (more than 2 lobes), or multifocal distribution
• Must be distinguished from: pulmonary edema, atypical infection, diffuse alveolar hemorrhage

Management of AE-IPF

• Broad-spectrum antibiotics (cover atypicals) if infection cannot be excluded
• Rule out pulmonary embolism (CT-PA if clinically suspected)
• Rule out heart failure (echo, BNP)
• BAL if feasible - to exclude infection

• Supplemental oxygen
• Mechanical ventilation - controversial; poor outcomes; not recommended unless as bridge to lung transplantation
• High-flow nasal cannula (HFNC) or non-invasive ventilation (NIV) may be tried
• Thromboprophylaxis

• No RCT has demonstrated benefit for any treatment in AE-IPF
• Rationale for steroids: suppress cellular/humoral immunity, reduce acute inflammation
• Current guidelines: weak recommendation to use corticosteroids in AE-IPF; appropriate dose, route, and duration unknown
• Direct hemoperfusion with polymyxin B-immobilized fiber column (PMX-F): some reports of benefit (binds endotoxin, cytokines, neutrophil elastase) - not standard therapy

Prognosis of AE-IPF

• Very poor - in-hospital mortality >50%, often approaching 70-80%
• Median survival after AE-IPF: weeks to a few months
• Survivors often have accelerated progressive decline
• AE-IPF represents a major cause of IPF-related death

10. COMORBIDITIES IN IPF

11. DIFFERENTIAL DIAGNOSIS

12. PROGNOSIS

• IPF carries a poor prognosis: median survival 3-5 years from diagnosis
• 50% 3-5 year survival rate
• Disease course: slow progressive decline in most; some have accelerating decline punctuated by AE episodes
• Poor prognostic factors:
  • FVC decline >10% in 6 months
  • DLCO <40% predicted
  • SpO2 <88% on 6MWT
  • Pulmonary hypertension
  • Honeycombing on HRCT
  • AE-IPF episodes
  • GAP score (Gender, Age, Physiology) - validated prognostic model

13. SUMMARY TABLE: AE-IPF AT A GLANCE

Recent Evidence Update (2023-2025)