Interstitial Lung Disease

Quick Reference

Critical Alerts

• Acute exacerbation of IPF carries 50-90% in-hospital mortality and requires immediate ICU consultation [1,2]
• UIP pattern on HRCT can diagnose IPF without surgical biopsy in appropriate clinical context [3]
• Antifibrotic therapy (pirfenidone, nintedanib) reduces FVC decline by ~50% and should be initiated early [4,5]
• Immunosuppression is harmful in IPF - avoid azathioprine, N-acetylcysteine, and prednisone combinations [6]
• Pulmonary hypertension develops in 30-50% of advanced ILD and significantly worsens prognosis [7]
• Drug-induced ILD may be reversible if offending agent stopped early [8]

Key Diagnostics

• HRCT chest: Gold standard for diagnosis and pattern recognition (UIP, NSIP, HP, sarcoid)
• Pulmonary function tests: Restrictive pattern (↓TLC, ↓FVC, ↓DLCO, preserved/↑FEV1/FVC)
• Six-minute walk test: Baseline SpO2 desaturation predicts mortality
• Bronchoalveolar lavage: Lymphocytosis (HP, NSIP), neutrophilia (IPF, acute exacerbation)
• Serology: ANA, RF, anti-CCP, anti-Scl-70, anti-Jo-1, myositis panel for CTD-ILD
• Serum biomarkers: KL-6, MMP-7, SP-D correlate with disease severity and progression

Emergency Treatments

• Acute exacerbation IPF: High-dose methylprednisolone 500-1000mg IV daily × 3 days, empiric antibiotics
• Supplemental oxygen: Target SpO2 88-92%; long-term oxygen if resting PaO2 less than 55mmHg or SpO2 less than 88%
• Mechanical ventilation: Lung-protective strategy (Vt 6ml/kg, Pplat less than 30cmH2O); discuss prognosis
• COP/inflammatory ILD: Prednisone 0.5-1mg/kg/day with excellent response expected
• Hypersensitivity pneumonitis: Antigen avoidance + corticosteroids

Chronic Disease Management

• IPF antifibrotic therapy: Pirfenidone 2403mg/day OR nintedanib 300mg/day
• CTD-ILD immunosuppression: Mycophenolate mofetil 2-3g/day or azathioprine 2mg/kg/day
• Pulmonary rehabilitation: Improves 6MWD, dyspnea scores, and quality of life
• Transplant referral criteria: DLCO less than 40%, FVC less than 80% or decline > 10% in 6 months, SpO2 less than 88% on 6MWT

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Definition and Classification

Interstitial lung disease (ILD), also termed diffuse parenchymal lung disease (DPLD), encompasses over 200 heterogeneous disorders characterized by inflammation and/or fibrosis of the lung interstitium—the tissue and space between alveolar epithelium and capillary endothelium. [3]

Comprehensive Classification

1. Idiopathic Interstitial Pneumonias (IIPs)

Major IIPs

Rare IIPs

• Lymphoid interstitial pneumonia (LIP): Associated with autoimmune disorders, Sjögren's syndrome
• Pleuroparenchymal fibroelastosis (PPFE): Upper lobe pleural and parenchymal fibrosis

2. ILD with Known Etiologies

Connective Tissue Disease-Associated ILD (CTD-ILD)

• Systemic sclerosis (SSc-ILD): Most common CTD to cause ILD; 40-75% develop ILD [9]
• Rheumatoid arthritis (RA-ILD): 10-20% of RA patients; UIP pattern has poor prognosis
• Polymyositis/dermatomyositis: NSIP or organizing pneumonia patterns; anti-synthetase syndrome
• Sjögren's syndrome: LIP, NSIP, or follicular bronchiolitis
• Systemic lupus erythematosus: Rare ILD; more commonly pleural or vascular disease
• Mixed connective tissue disease: Overlapping features

Environmental and Occupational ILD

Drug-Induced ILD

Common culprits and patterns: [8]

Hypersensitivity Pneumonitis (HP)

Antigen-mediated immune response to inhaled organic or chemical antigens: [10]

Classification by clinical presentation:

• Acute: Hours to days; flu-like illness with dyspnea
• Subacute: Weeks to months; progressive dyspnea
• Chronic: Years; irreversible fibrosis mimicking IPF

Radiation-Induced Lung Injury

• Radiation pneumonitis: 1-6 months post-radiation; confined to radiation field
• Radiation fibrosis: Months to years; irreversible

3. Granulomatous ILDs

Sarcoidosis

Multisystem granulomatous disease of unknown etiology: [11]

• Epidemiology: Peak age 20-40 years; higher incidence in African Americans and Scandinavians
• Stages (Scadding classification):
  • "Stage 0: Normal CXR (5%)"
  • "Stage I: Bilateral hilar lymphadenopathy alone (50%)"
  • "Stage II: Hilar adenopathy + parenchymal infiltrates (30%)"
  • "Stage III: Parenchymal infiltrates without adenopathy (10%)"
  • "Stage IV: Pulmonary fibrosis (5%)"
• Prognosis: Stages I-II often self-limiting; Stage IV irreversible

Hypersensitivity Pneumonitis (described above)

4. Other ILD Entities

Eosinophilic Pneumonias

• Acute eosinophilic pneumonia: Acute febrile illness; BAL > 25% eosinophils; steroid-responsive
• Chronic eosinophilic pneumonia: Peripheral consolidation ("photographic negative of pulmonary edema")

Pulmonary Alveolar Proteinosis (PAP)

• Accumulation of surfactant in alveoli
• Autoimmune (anti-GM-CSF antibodies), secondary, or congenital
• "Crazy paving" pattern on HRCT
• Treatment: Whole lung lavage

Lymphangioleiomyomatosis (LAM)

• Rare; affects women of childbearing age
• Cystic lung disease with pneumothorax risk
• Associated with tuberous sclerosis complex
• Treatment: Sirolimus (mTOR inhibitor)

Langerhans Cell Histiocytosis (Pulmonary)

• Smoking-related; young adults
• Stellate nodules and cysts; upper/mid zone predominance
• Treatment: Smoking cessation

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Epidemiology

Idiopathic Pulmonary Fibrosis (as prototype) [3,12]

• Incidence: 3-9 per 100,000 person-years in the USA; 0.5-8 per 100,000 globally
• Prevalence: 14-43 per 100,000; increasing over time (improved recognition vs. true increase debated)
• Age: Typically > 60 years; rare before age 50; mean age at diagnosis 66 years
• Sex: Male predominance 1.5-2:1
• Ethnicity: Higher prevalence in non-Hispanic whites
• Risk factors:
  • Cigarette smoking (OR 1.6-2.3)
  • Environmental/occupational exposures (metal dust, wood dust, agriculture)
  • Gastroesophageal reflux disease
  • Chronic viral infections (EBV, HHV)
  • Genetic predisposition (familial pulmonary fibrosis 5-20%; mutations in surfactant proteins, telomerase genes)
• Median survival: 3-5 years from diagnosis (worse than many cancers); improved with antifibrotic therapy

Other ILD Epidemiology

• NSIP: Second most common IIP; often idiopathic or associated with CTD
• COP: Incidence 1-2 per 100,000; no sex predominance; mean age 55 years
• HP: Prevalence varies by occupation/exposure; farmers 0.4-7%, bird breeders 6-20%
• Sarcoidosis: Incidence 5-40 per 100,000; African Americans 3× higher than whites
• SSc-ILD: Develops in 40-75% of systemic sclerosis patients; leading cause of SSc mortality
• RA-ILD: 10-20% of RA patients; more common in males, smokers, and seropositive RA

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Pathophysiology

General Mechanisms of Fibrogenesis

The pathway from lung injury to fibrosis involves: [12,13]

1. Epithelial Injury and Activation

• Alveolar epithelial cell (AEC) damage from injury (infection, environmental, autoimmune, idiopathic)
• AEC apoptosis and inadequate re-epithelialization
• Loss of alveolar-capillary barrier integrity
• Release of pro-fibrotic mediators: TGF-β, PDGF, CTGF, endothelin-1

2. Inflammatory Cell Recruitment

• Macrophage accumulation and M2 (pro-fibrotic) polarization
• Neutrophil infiltration (associated with worse prognosis in IPF)
• Lymphocyte recruitment (variable; prominent in NSIP and HP)
• Release of cytokines: IL-1β, IL-6, IL-8, TNF-α

3. Fibroblast Activation and Myofibroblast Differentiation

• Fibroblast proliferation and migration to injury sites
• Transformation to myofibroblasts (express α-smooth muscle actin)
• Myofibroblasts resist apoptosis and persist in fibrotic foci
• Formation of fibroblastic foci (hallmark of UIP/IPF)

4. Extracellular Matrix Deposition

• Excessive collagen synthesis (predominantly types I and III)
• Imbalance between matrix metalloproteinases (MMPs) and tissue inhibitors (TIMPs)
• Progressive architectural distortion
• Honeycombing: cystic spaces representing destroyed and remodeled lung

5. Aberrant Vascular Remodeling

• Pulmonary vascular obliteration and rarefaction
• Pulmonary hypertension development
• Hypoxic pulmonary vasoconstriction
• Right ventricular dysfunction (cor pulmonale)

Disease-Specific Pathophysiology

Idiopathic Pulmonary Fibrosis (IPF)

Current paradigm: Epithelial injury and aberrant repair rather than chronic inflammation [12]

Key Features:

• Recurrent micro-injuries to aging alveolar epithelium
• Epithelial cell senescence and apoptosis
• Abnormal wound healing with fibroblast/myofibroblast persistence
• Minimal inflammation (distinguishes from other ILDs)
• Genetic susceptibility: MUC5B promoter polymorphism (OR 5-10 for IPF), telomerase mutations
• Epigenetic changes and cellular senescence
• Mitochondrial dysfunction and oxidative stress

Histopathologic Pattern: Usual Interstitial Pneumonia (UIP)

• Temporal heterogeneity: Areas of normal lung adjacent to fibrotic zones
• Spatial heterogeneity: Patchy distribution; subpleural and basilar predominance
• Fibroblastic foci: Active fibrosis at edge of scarred lung
• Honeycombing: End-stage cystic remodeling
• Minimal inflammation

Nonspecific Interstitial Pneumonia (NSIP)

Key Features:

• Temporally uniform process (unlike UIP's heterogeneity)
• Two patterns:
  • "Cellular NSIP: Predominantly interstitial inflammation"
  • "Fibrotic NSIP: Interstitial fibrosis with inflammation"
• Architecture generally preserved (no honeycombing)
• Better response to immunosuppression than IPF

Organizing Pneumonia (OP)

Key Features:

• Granulation tissue plugs within alveolar ducts and alveoli ("Masson bodies")
• Preservation of lung architecture
• Patchy distribution
• Responsive to corticosteroids (granulation tissue resorbs)
• COP: No identifiable cause; secondary OP: infection, drugs, CTD

Hypersensitivity Pneumonitis

Acute HP:

• Immune complex-mediated (Type III hypersensitivity)
• Neutrophilic alveolitis
• Interstitial edema and mononuclear cell infiltration
• Reversible with antigen avoidance

Chronic HP:

• Granulomatous inflammation (poorly formed, non-necrotizing)
• Bronchiolocentric distribution
• Cellular bronchiolitis and peribronchiolar metaplasia
• Progressive fibrosis (may mimic UIP in end-stage)

Sarcoidosis

Key Features:

• Non-caseating epithelioid granulomas
• Perilymphatic distribution (along bronchovascular bundles, interlobular septa, pleura)
• CD4+ T-helper cell predominance
• Activated macrophages producing TNF-α, IL-12, IFN-γ
• Spontaneous resolution in 60-70%; chronic/progressive in 10-30%

Respiratory Physiology in ILD

Restrictive Ventilatory Defect

Pulmonary Function Tests:

• ↓ Total lung capacity (TLC) less than 80% predicted (hallmark of restriction)
• ↓ Forced vital capacity (FVC)
• ↓ Residual volume (RV) and functional residual capacity (FRC)
• Preserved or ↑ FEV1/FVC ratio (> 0.7 or > 70%)
• ↓ Lung compliance (stiff lungs require greater pressure for ventilation)
• ↓ Diffusing capacity for carbon monoxide (DLCO) - often earliest abnormality

Progression Markers:

• FVC decline ≥10% predicts mortality
• DLCO decline correlates with disease severity
• Composite physiologic index (CPI) integrates FVC, FEV1, and DLCO

Gas Exchange Abnormalities

Mechanisms:

• Thickened alveolar-capillary membrane → diffusion impairment
• V/Q mismatch from heterogeneous fibrosis
• Shunt physiology in consolidated/atelectatic regions
• Reduced pulmonary capillary blood volume

Clinical Consequences:

• Hypoxemia (initially exertional, then resting)
• Widened A-a gradient
• Exercise-induced desaturation (6MWT SpO2 nadir less than 88% predicts mortality)
• Hypercapnia rare until end-stage disease (increased minute ventilation compensates)

Pulmonary Hypertension in ILD [7]

Prevalence:

• IPF: 30-50% at diagnosis; > 80% at transplant evaluation
• CTD-ILD: 5-15% (higher in SSc)
• Sarcoidosis: 5-15%

Mechanisms:

• Hypoxic pulmonary vasoconstriction
• Vascular destruction and rarefaction from fibrosis
• Vascular remodeling: intimal proliferation, medial hypertrophy
• Left heart dysfunction (Group 2 PH)
• Chronic thromboembolic disease (rare)

Hemodynamic Criteria:

• Mean pulmonary artery pressure (mPAP) ≥20 mmHg
• Pulmonary vascular resistance (PVR) > 3 Wood units
• Pulmonary artery wedge pressure (PAWP) ≤15 mmHg

Prognostic Impact:

• Presence of PH reduces median survival by 50%
• Independent predictor of mortality even with mild elevation

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Clinical Presentation

Chronic Progressive Symptoms

Cardinal Symptoms [3]

Dyspnea

• Insidious onset; progressive over months to years
• Initially exertional (climbing stairs, walking uphill)
• Advances to dyspnea at rest in severe disease
• Often attributed to aging, deconditioning, or cardiac disease (diagnostic delay common)
• Mean symptom duration before diagnosis: 1-2 years

Dry Cough

• Non-productive, persistent, irritating
• Present in 70-80% of IPF patients
• May be sole presenting symptom
• Refractory to antitussives
• Impairs quality of life significantly

Exercise Intolerance

• Reduced exercise capacity on 6-minute walk test (6MWT)
• Oxygen desaturation during exertion (SpO2 decline > 4% or nadir less than 88%)
• Correlates with disease severity and prognosis
• Dyspnea scores: mMRC (modified Medical Research Council) or SOBOE (shortness of breath on exertion)

Fatigue

• Underappreciated symptom
• Multifactorial: hypoxemia, sleep disruption, inflammation, depression
• Impacts daily activities and quality of life

Disease-Specific Presentations

Symptoms Suggesting Specific Etiologies

Connective Tissue Disease (CTD-ILD)

• Arthralgias, morning stiffness, joint swelling
• Raynaud's phenomenon (SSc, MCTD)
• Skin changes: sclerodactyly, puffy fingers, digital ulcers (SSc)
• Mechanic's hands (anti-synthetase syndrome)
• Heliotrope rash, Gottron's papules (dermatomyositis)
• Photosensitive rash, oral ulcers, serositis (SLE)
• Sicca symptoms (Sjögren's syndrome)

Environmental/Occupational

• Detailed occupational history: mining, sandblasting, construction, metalwork
• Hobbies: bird keeping, hot tubs, woodworking
• Agricultural work: handling hay, grain, silage
• Residence history: water damage, mold exposure

Drug-Induced ILD

• Temporal relationship to new medication (onset during or after therapy)
• Common culprits: amiodarone, methotrexate, nitrofurantoin, checkpoint inhibitors
• Symptom improvement after drug discontinuation

Physical Examination

Pulmonary Findings

Inspiratory Crackles ("Velcro crackles") [3]

• Fine, end-inspiratory, bibasilar crackles
• "Velcro-like" quality (sound of separating Velcro)
• Present in > 90% of IPF patients
• Hallmark of fibrotic ILD
• Persist throughout respiratory cycle (vs. early inspiratory crackles in COPD)
• May be absent in early disease

Clubbing

• Digital clubbing present in 25-50% of IPF patients
• Less common in other ILDs except asbestosis
• Associated with more advanced disease
• Loss of Lovibond angle (> 180°)
• Increased nail bed fluctuance (Schamroth sign)

Other Findings

• Tachypnea (respiratory rate > 20/min in advanced disease)
• Shallow breathing pattern (restrictive physiology)
• Accessory muscle use (severe dyspnea)
• Cyanosis (severe hypoxemia; central cyanosis with SpO2 less than 85%)

Cardiovascular Findings (Pulmonary Hypertension/Cor Pulmonale)

Right Ventricular Failure

• Elevated jugular venous pressure (JVP)
• Prominent v-waves (tricuspid regurgitation)
• Hepatojugular reflux
• Peripheral edema (lower extremities, sacral)
• Ascites (severe RV failure)
• Hepatomegaly (pulsatile liver in TR)

Cardiac Auscultation

• Loud P2 (pulmonary component of second heart sound)
• Fixed split S2 (severe PH)
• Right ventricular S3 or S4 gallop
• Pansystolic murmur at left sternal border (tricuspid regurgitation; increases with inspiration - Carvallo sign)

Other Signs

• Parasternal heave/lift (RV hypertrophy)
• Palpable P2 (pulmonary artery pulsation)

Extrapulmonary Findings (Suggest Secondary ILD)

Connective Tissue Disease

• Sclerodactyly, skin tightening (SSc)
• Digital ulcers, calcinosis (SSc)
• Mechanic's hands: hyperkeratosis and cracking of palms/fingers (anti-synthetase syndrome)
• Heliotrope rash: violaceous periorbital edema (dermatomyositis)
• Gottron's papules: erythematous papules over MCP/PIP joints (dermatomyositis)
• Shawl sign: erythema over upper back/shoulders (dermatomyositis)
• Malar rash (SLE)
• Joint swelling, synovitis, deformities (RA)

Sarcoidosis

• Skin: erythema nodosum, lupus pernio, scar infiltration
• Eyes: uveitis, conjunctival nodules
• Lymphadenopathy: peripheral, hepatosplenomegaly
• Neurologic: cranial nerve palsies (CN VII most common), peripheral neuropathy
• Cardiac: heart block, arrhythmias, cardiomyopathy

Other

• Telangiectasias (SSc, HHT)
• Adenopathy (sarcoidosis, lymphoma, infection)

Acute Exacerbation of Interstitial Lung Disease

Definition and Diagnostic Criteria [1,2]

Acute Exacerbation of IPF (AE-IPF):

Consensus definition requires ALL of the following:

1. Previous or concurrent diagnosis of IPF
2. Acute worsening or development of dyspnea, typically less than 30 days
3. HRCT: New bilateral ground-glass opacities and/or consolidation superimposed on background reticular or honeycomb pattern
4. Deterioration not fully explained by cardiac failure or fluid overload

Categories:

• Triggered AE-IPF: Identifiable precipitant (infection, aspiration, procedure, drugs)
• Idiopathic AE-IPF: No identifiable trigger despite thorough investigation

Incidence: 5-15% of IPF patients per year; cumulative risk increases with disease duration

Clinical Presentation

Symptoms:

• Rapid worsening of dyspnea over days to weeks
• Increased cough (may become productive if infection)
• Worsening hypoxemia (increased oxygen requirement or new oxygen need)
• Fever (suggests infection but may be absent)
• Pleuritic chest pain (uncommon)

Physical Examination:

• Tachypnea, labored breathing
• Accessory muscle use
• New or worsened inspiratory crackles
• Cyanosis
• Signs of respiratory failure

Prognosis [1,2]

• In-hospital mortality: 50-90% (varies by series; recent data suggest ~60-70%)
• Median survival from AE: 3-4 months
• ICU outcomes: Mechanical ventilation associated with > 90% mortality
• Recurrence risk: Survivors at high risk for subsequent acute exacerbations

Differential Diagnosis of Acute Worsening

Must exclude:

• Infection: Pneumonia (bacterial, viral, fungal, PJP)
• Pulmonary embolism
• Heart failure (acute decompensation)
• Pneumothorax (especially in cystic ILD)
• Drug toxicity (chemotherapy, amiodarone)
• Aspiration
• Diffuse alveolar hemorrhage
• Progression of underlying ILD without acute exacerbation

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Red Flags and Life-Threatening Presentations

Immediate Life Threats

Acute Exacerbation of IPF - Specific Alerts [1,2]

High-Risk Features for AE-IPF:

• Baseline FVC less than 50% predicted
• DLCO less than 35% predicted
• Pulmonary hypertension
• Recent surgical procedures (especially non-thoracic surgery: OR 2-4)
• GAP index stage III (Gender-Age-Physiology)

Triggers Requiring Identification:

• Infection (most common trigger - 40-50%): viral > bacterial > atypical
• Aspiration events
• Invasive procedures: lung biopsy, bronchoscopy, surgery
• Drug toxicity
• Radiation pneumonitis

Pulmonary Hypertension Crisis

Presentation:

• Severe dyspnea, chest pressure
• Syncope or pre-syncope (reduced cardiac output)
• Right heart failure decompensation (edema, ascites, hepatic congestion)

Management:

• Avoid hypoxemia (critical - worsens PVR)
• Treat underlying ILD exacerbation
• Diuretics for volume overload (caution: maintain preload to RV)
• Oxygen therapy
• Pulmonology/cardiology consultation
• Consider right heart catheterization

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Differential Diagnosis

Acute Presentations

Chronic ILD Differential by HRCT Pattern

Usual Interstitial Pneumonia (UIP) Pattern [3]

HRCT Features:

• Subpleural and basilar predominance
• Reticular opacities
• Honeycombing (clustered cystic airspaces, typically subpleural, 3-10mm)
• Traction bronchiectasis/bronchiolectasis
• Absence of features inconsistent with UIP (see below)

Diagnostic Confidence:

• UIP pattern: Honeycombing ± traction bronchiectasis → IPF diagnosis without biopsy in appropriate clinical context
• Probable UIP: Traction bronchiectasis without honeycombing → May diagnose IPF or consider biopsy
• Indeterminate for UIP: Subtle reticulation, lacks defining features → Biopsy often needed
• Alternative diagnosis: Features inconsistent with UIP (see below)

Features INCONSISTENT with UIP (suggest alternative diagnosis):

• Consolidation
• Ground-glass attenuation (predominant)
• Mosaic attenuation/air trapping (extensive)
• Predominant centrilobular nodules
• Predominant upper or mid-lung distribution
• Peribronchovascular predominance

Differential Diagnosis of UIP Pattern:

• Idiopathic pulmonary fibrosis (most common)
• Connective tissue disease-UIP (RA, SSc)
• Chronic hypersensitivity pneumonitis (may have UIP in end-stage; clues: upper lobe involvement, air trapping, exposures)
• Drug-induced fibrosis (nitrofurantoin, chemotherapy)
• Asbestosis (pleural plaques, exposure history)
• Familial pulmonary fibrosis

Nonspecific Interstitial Pneumonia (NSIP) Pattern

HRCT Features:

• Bilateral ground-glass opacities (cellular NSIP) or reticular opacities (fibrotic NSIP)
• Subpleural sparing (key differentiator from UIP)
• Lower lobe predominance
• Traction bronchiectasis in fibrotic NSIP
• Minimal honeycombing (if present, limited)

Differential Diagnosis:

• Idiopathic NSIP
• Connective tissue disease-ILD (most common cause; SSc, myositis, Sjögren's)
• Drug-induced ILD
• Chronic hypersensitivity pneumonitis
• Organizing pneumonia (overlap features)

Organizing Pneumonia (OP) Pattern

HRCT Features:

• Patchy bilateral consolidation or ground-glass opacities
• Peribronchovascular or subpleural distribution
• Lower lobe predominance
• "Reverse halo" or "atoll" sign: Central ground-glass surrounded by denser consolidation (specific but not sensitive)
• Migratory opacities (may change location on serial imaging)
• Nodular opacities

Differential Diagnosis:

• Cryptogenic organizing pneumonia (COP) - idiopathic
• Secondary OP: Infection (viral, bacterial), drugs, connective tissue disease, radiation

Hypersensitivity Pneumonitis (HP) Pattern [10]

Acute/Subacute HP:

• Diffuse ground-glass opacities
• Centrilobular ground-glass nodules (poorly defined)
• Mosaic attenuation
• Air trapping on expiratory images (three-density pattern)
• Mid-to-upper lung predominance

Chronic Fibrotic HP:

• Reticular opacities
• Traction bronchiectasis
• Ground-glass opacities
• Mosaic attenuation and air trapping
• Upper and mid-lung predominance (key differentiator from IPF)
• Cysts (may mimic honeycombing but irregular shape)

Differential:

• Sarcoidosis (perilymphatic nodules, adenopathy)
• NSIP (subpleural sparing, lower lobe)
• UIP (basilar, no air trapping)

Sarcoidosis Pattern [11]

HRCT Features:

• Perilymphatic nodules (along bronchovascular bundles, interlobular septa, pleura)
• Bilateral hilar and mediastinal lymphadenopathy (often symmetric)
• Upper and mid-lung predominance
• Irregular linear opacities along bronchovascular bundles
• Conglomerate masses (progressive massive fibrosis in Stage IV)
• Ground-glass opacities (alveolitis)
• Architectural distortion, traction bronchiectasis (fibrotic stages)

Differential:

• Silicosis/Coal worker's pneumoconiosis (occupational exposure, upper lobe, nodules)
• Lymphangitic carcinomatosis (asymmetric, pleural effusion, known malignancy)
• Chronic HP (more ground-glass, mosaic attenuation)

Other Patterns

Cystic Lung Diseases:

• LAM: Diffuse thin-walled cysts, uniform size, uniform distribution; women of childbearing age
• Langerhans cell histiocytosis: Bizarre-shaped cysts, spares costophrenic angles, upper/mid lung; smokers
• Lymphocytic interstitial pneumonia (LIP): Thin-walled cysts, ground-glass, associated with Sjögren's

Crazy Paving:

• Ground-glass opacities with superimposed interlobular septal thickening
• Differential: Pulmonary alveolar proteinosis (most classic), PJP, ARDS, DAH, pulmonary edema

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Diagnostic Approach

Initial Evaluation

History [3]

Detailed Symptom Assessment:

• Onset, duration, progression of dyspnea and cough
• Exercise tolerance (quantify: stairs climbed, distance walked)
• Orthopnea, paroxysmal nocturnal dyspnea (suggest cardiac)
• Hemoptysis, chest pain, weight loss, fever

Medication History:

• Complete list including over-the-counter, supplements
• Focus on high-risk drugs: amiodarone, methotrexate, nitrofurantoin, biologics, chemotherapy
• Temporal relationship between drug initiation and symptom onset

Exposure History:

• Occupational: Current and all previous jobs; specific tasks; protective equipment
• Environmental: Birds, hot tubs, humidifiers, water damage, mold
• Hobbies: Woodworking, metalworking, pottery, painting
• Residence: Geographic location (fibrosis clusters), home age/condition

Smoking History:

• Pack-years (increases IPF risk)
• Current vs. former (RB-ILD and DIP in current smokers)

Family History:

• First-degree relatives with pulmonary fibrosis (familial pulmonary fibrosis)
• Autoimmune diseases

Review of Systems:

• Connective tissue disease symptoms (arthritis, rash, Raynaud's, sicca, myalgias)
• Constitutional symptoms (fever, weight loss, night sweats)

Physical Examination

(Detailed in Clinical Presentation section above)

Laboratory Studies

Routine Studies

Serologic Testing for CTD-ILD [9]

Recommended in all patients with unexplained ILD:

Interpretation:

• Isolated low-titer ANA common in IPF; does not indicate CTD
• High-titer ANA or multiple positive antibodies suggest CTD-ILD
• ILD may precede other CTD manifestations by months to years ("lung-dominant CTD")

Biomarkers for ILD Prognosis (Research/Emerging)

Pulmonary Function Tests (PFTs) [3]

Essential for diagnosis, severity assessment, and monitoring.

Spirometry and Lung Volumes

Classic Restrictive Pattern:

• ↓ Total lung capacity (TLC) less than 80% predicted (definitive for restriction)
• ↓ Forced vital capacity (FVC)
• ↓ Residual volume (RV)
• ↓ Functional residual capacity (FRC)
• Preserved or ↑ FEV1/FVC ratio ≥0.70 (distinguishes from obstructive disease)

Severity Classification by FVC:

• Mild: FVC ≥70%
• Moderate: FVC 50-69%
• Severe: FVC less than 50%

Notes:

• Early ILD may have normal spirometry
• Mixed pattern possible (IPF + emphysema = "combined pulmonary fibrosis and emphysema" [CPFE])

Diffusing Capacity (DLCO)

• ↓ DLCO (often earliest and most sensitive PFT abnormality)
• Reduced due to: thickened alveolar-capillary membrane, reduced capillary surface area, V/Q mismatch

Severity by DLCO:

• Mild: 60-79% predicted
• Moderate: 40-59% predicted
• Severe: less than 40% predicted

DLCO disproportionately reduced (vs. FVC) in:

• Pulmonary hypertension
• Emphysema component (CPFE)
• Pulmonary vascular disease

Exercise Testing

Six-Minute Walk Test (6MWT):

• Distance walked in 6 minutes
• Continuous SpO2 monitoring

Prognostic Significance:

• Baseline 6MWD less than 250m predicts mortality
• SpO2 nadir less than 88% or desaturation ≥4% predicts mortality
• Decline in 6MWD over time indicates progression

Cardiopulmonary Exercise Testing (CPET):

• Peak VO2 (maximal oxygen consumption)
• Ventilatory efficiency (VE/VCO2 slope)
• Identifies gas exchange impairment, pulmonary vascular limitation
• Used in transplant evaluation

Imaging

Chest Radiography

Findings:

• Reduced lung volumes
• Reticular or reticulonodular opacities (lower zones in IPF)
• Honeycomb pattern (advanced fibrosis)
• Hilar/mediastinal lymphadenopathy (sarcoidosis, lymphoma)

Limitations:

• May be normal in early ILD (up to 10-15%)
• Poor sensitivity and specificity
• Cannot distinguish ILD subtypes reliably

Utility:

• Initial screening
• Monitoring disease progression (limited)
• Identifying complications (pneumothorax, infection)

High-Resolution Computed Tomography (HRCT) [3]

Gold standard for ILD diagnosis and characterization.

Technique:

• Thin-section CT (1-2mm slice thickness)
• Supine inspiratory images
• Prone images (differentiate dependent atelectasis from fibrosis)
• Expiratory images (assess air trapping in HP, RB-ILD)

Diagnostic Patterns: (See Differential Diagnosis section for detailed descriptions)

• UIP pattern → IPF (in appropriate clinical context)
• NSIP pattern → Idiopathic NSIP or CTD-ILD
• Organizing pneumonia pattern → COP or secondary OP
• HP pattern → Hypersensitivity pneumonitis
• Sarcoidosis pattern → Sarcoidosis
• Cystic pattern → LAM, LCH, LIP

Acute Exacerbation Findings:

• New bilateral ground-glass opacities
• New consolidation
• Superimposed on pre-existing UIP pattern
• Typically peripheral and/or subpleural distribution

Quantitative CT:

• Computer-aided analysis of fibrosis extent
• Predicts disease progression and mortality
• Used in clinical trials

Other Imaging

Echocardiography:

• Assess for pulmonary hypertension (elevated RVSP, RV dilation/dysfunction, TR)
• Estimate pulmonary artery systolic pressure (PASP)
• Evaluate left ventricular function (exclude cardiac etiology)

Positron Emission Tomography (PET-CT):

• Differentiate active inflammation from fibrosis (FDG uptake)
• Assess sarcoidosis activity
• Exclude malignancy

Bronchoscopy and Bronchoalveolar Lavage (BAL)

Indications

• Exclude infection (immunocompromised, acute presentation)
• Evaluate suspected HP, eosinophilic pneumonia, DAH, PAP
• Assess inflammation in NSIP, COP (cellular vs. fibrotic)
• When diagnosis uncertain after non-invasive workup

BAL Cell Differential

Normal:

• Macrophages 80-90%
• Lymphocytes 10-15%
• Neutrophils less than 3%
• Eosinophils less than 1%

Disease-Specific Patterns:

Transbronchial Biopsy

• Small tissue samples via bronchoscope
• Adequate for sarcoidosis (non-caseating granulomas), eosinophilic pneumonia, organizing pneumonia, infection
• Inadequate for IPF/UIP diagnosis (small sample size, sampling error)
• Complications: pneumothorax (1-5%), bleeding

Transbronchial Cryobiopsy

• Larger tissue samples than forceps biopsy
• Better diagnostic yield for ILD
• May diagnose UIP without surgical biopsy
• Complications: pneumothorax (10-15%), bleeding (moderate 10%, severe less than 1%)
• Availability limited; requires expertise

Surgical Lung Biopsy

Indications [3]

Consider when:

• Diagnosis uncertain after non-invasive evaluation (HRCT, serology, BAL)
• Treatment implications depend on histopathology
• Patient is a candidate for interventions based on diagnosis

NOT required when:

• Typical UIP pattern on HRCT in appropriate clinical context (age > 60, gradual onset dyspnea, bibasilar crackles, no CTD features) → Diagnose IPF clinically
• Diagnosis obvious from clinical/radiologic features (e.g., definite sarcoidosis, HP with exposure)
• Patient not a candidate for treatment (comorbidities, frailty)

Approach

Video-Assisted Thoracoscopic Surgery (VATS):

• Multiple biopsies from different lobes (at least 2-3 sites)
• Includes areas of most and least involvement
• Gold standard for histopathologic diagnosis

Open Surgical Biopsy:

• Reserved for patients not candidates for VATS
• Higher morbidity than VATS

Complications:

• Pneumothorax, prolonged air leak
• Bleeding
• Acute exacerbation of ILD (1-10%; higher mortality in IPF)
• Respiratory failure

Multidisciplinary Discussion (MDD) [3]

Gold standard for ILD diagnosis - improves diagnostic confidence and accuracy.

Participants:

• Pulmonologist
• Radiologist (ILD-experienced)
• Pathologist (if biopsy performed)

Process:

• Integrate clinical features, HRCT pattern, histopathology (if available)
• Reach consensus diagnosis
• Formulate management plan

Outcomes:

• Diagnosis changed in 30-50% of cases after MDD
• Improved diagnostic confidence
• Better patient outcomes

---

Treatment

General Principles

Management Approach Depends on ILD Subtype:

• Fibrotic, progressive ILDs (IPF, fibrotic NSIP): Antifibrotic therapy, supportive care, transplant evaluation
• Inflammatory ILDs (NSIP, COP, HP, CTD-ILD): Immunosuppression often effective
• Granulomatous ILDs (sarcoidosis): Observation vs. immunosuppression based on severity
• Secondary ILDs: Remove causative agent (antigen, drug) + immunosuppression if needed

Goals of Therapy:

• Slow disease progression
• Preserve lung function
• Improve symptoms and quality of life
• Prevent acute exacerbations
• Prolong survival
• Identify transplant candidates early

Disease-Specific Pharmacotherapy

Idiopathic Pulmonary Fibrosis (IPF) [3,4,5]

Antifibrotic Agents - First-line therapy for all IPF patients with FVC ≥45-50%

Pirfenidone:

• Mechanism: Antifibrotic, anti-inflammatory; reduces TGF-β, TNF-α, PDGF
• Dosing: Titrate to 2403 mg/day (801 mg TID with food)
  • "Week 1: 267 mg TID"
  • "Week 2: 534 mg TID"
  • "Week 3+: 801 mg TID"
• Efficacy: [4]
  • Reduces FVC decline by ~50% (relative)
  • Reduces mortality (meta-analysis HR 0.52)
  • Improves progression-free survival
• Adverse Effects:
  • "GI upset (nausea, dyspepsia, diarrhea) 30-40%: take with food, dose adjustments"
  • "Photosensitivity rash 10-20%: sun protection, avoid UV"
  • "Elevated LFTs: monitor monthly × 6 months, then quarterly"
  • Fatigue, dizziness
• Monitoring: LFTs monthly × 6 months, then every 3 months
• Contraindications: Severe hepatic impairment, end-stage renal disease, concurrent fluvoxamine

Nintedanib:

• Mechanism: Tyrosine kinase inhibitor; inhibits PDGF, FGF, VEGF receptors
• Dosing: 150 mg PO BID (reduce to 100 mg BID if intolerance)
• Efficacy: [5]
  • Reduces FVC decline by ~50% (relative)
  • Slows disease progression
  • Reduces acute exacerbations (pooled analysis)
• Adverse Effects:
  • "Diarrhea 60-70% (most common): loperamide as needed, dietary modifications"
  • "Nausea 20-30%: antiemetics, take with food"
  • "Elevated LFTs: monitor monthly × 3 months, then quarterly"
  • "Bleeding risk (theoretical): caution with anticoagulation"
  • "Arterial thromboembolic events (1-3%): caution in CV disease"
• Monitoring: LFTs monthly × 3 months, then every 3 months
• Contraindications: Severe hepatic impairment, pregnancy

Choosing Between Pirfenidone and Nintedanib:

• Similar efficacy in slowing FVC decline
• Choice based on side effect profile, drug interactions, patient comorbidities, cost
• Nintedanib preferred if concurrent malignancy (anti-VEGF effect)
• Pirfenidone preferred if diarrhea intolerable (less GI upset)
• No evidence for combination therapy (INJOURNEY trial: no added benefit, more AEs)

Corticosteroids and Immunosuppression in IPF:

• AVOID - No benefit and potential harm [6]
• PANTHER-IPF trial: Prednisone + azathioprine + N-acetylcysteine increased mortality and hospitalizations
• Monotherapy N-acetylcysteine: no benefit (PANTHER-IPF, CAPACITY)
• Exception: Acute exacerbation of IPF (empiric pulse steroids)

Nonspecific Interstitial Pneumonia (NSIP)

Cellular NSIP:

• Corticosteroids: Prednisone 0.5-1 mg/kg/day × 4-12 weeks, then taper
• Good response expected
• Add steroid-sparing agent if prolonged therapy needed

Fibrotic NSIP:

• Immunosuppression: Less responsive than cellular NSIP
• Mycophenolate mofetil 2-3 g/day OR azathioprine 2 mg/kg/day
• +/- Prednisone (start 0.5 mg/kg/day, taper)
• Consider antifibrotic therapy if progressive despite immunosuppression

Cryptogenic Organizing Pneumonia (COP)

First-Line:

• Prednisone 0.75-1 mg/kg/day (typically 40-60 mg/day) × 4-12 weeks
• Taper over 6-12 months total duration
• Monitor clinical and radiographic response (improvement in 1-2 weeks expected)

Expected Response:

• 80% respond to corticosteroids
• Relapse in 30-50% during taper → increase dose temporarily, slower taper
• Steroid-sparing agents (azathioprine, mycophenolate) if relapses or prolonged therapy

Hypersensitivity Pneumonitis (HP) [10]

Acute/Subacute HP:

• Antigen avoidance (most important)
• Corticosteroids: Prednisone 0.5-1 mg/kg/day × 4-12 weeks, taper over 6-12 months
• Usually reversible if antigen identified and avoided

Chronic Fibrotic HP:

• Antigen avoidance (still critical)
• Corticosteroids: Less responsive; try prednisone 0.5 mg/kg/day
• Mycophenolate or azathioprine: Consider adding if fibrotic
• Antifibrotic therapy: Nintedanib approved for progressive fibrosing ILD (includes HP)

Connective Tissue Disease-Associated ILD (CTD-ILD) [9]

Systemic Sclerosis-ILD (SSc-ILD):

• Mycophenolate mofetil 3 g/day: Superior to cyclophosphamide (SLS II trial)
• Cyclophosphamide (if severe): 600 mg/m² IV monthly × 6 months, then switch to maintenance
• Nintedanib: FDA-approved for SSc-ILD (SENSCIS trial: reduced FVC decline)
• Tocilizumab (anti-IL-6): Approved for SSc-ILD (focuSSced trial)

Rheumatoid Arthritis-ILD (RA-ILD):

• Immunosuppression: Mycophenolate, azathioprine, rituximab
• Avoid: Methotrexate (may worsen ILD), TNF inhibitors (associated with ILD)
• Nintedanib: May be beneficial for progressive RA-UIP

Anti-Synthetase Syndrome:

• Corticosteroids + immunosuppression (mycophenolate, azathioprine)
• Rituximab: Effective in refractory cases

Sarcoidosis [11]

Indications for Treatment:

• Symptomatic pulmonary disease (dyspnea, cough, declining PFTs)
• Extrapulmonary involvement: cardiac, neurologic, ocular, hypercalcemia, renal
• Stage II-IV with symptoms or progressive decline

NOT treated:

• Stage I (isolated hilar adenopathy) - often resolves spontaneously
• Asymptomatic Stage II-III with stable PFTs

First-Line:

• Prednisone 20-40 mg/day × 4-12 weeks, taper over 6-12 months
• Monitor FVC, DLCO, symptoms

Steroid-Sparing Agents (for relapse or prolonged therapy):

• Methotrexate 10-25 mg weekly (most common)
• Azathioprine 2 mg/kg/day
• Leflunomide 10-20 mg/day
• Mycophenolate 2-3 g/day

Refractory Sarcoidosis:

• Infliximab (anti-TNF): 5 mg/kg IV at 0, 2, 6 weeks, then every 4-8 weeks
• Adalimumab, rituximab: alternatives

Progressive Fibrosing ILD (PF-ILD)

Definition: Non-IPF ILD with progressive fibrosis despite therapy:

• Decline in FVC ≥10% or DLCO ≥15% in 12 months, OR
• Decline in FVC 5-10% + worsening symptoms/imaging

Examples: Fibrotic HP, fibrotic NSIP, CTD-ILD, unclassifiable ILD

Treatment:

• Nintedanib (FDA-approved for PF-ILD; INBUILD trial): reduced FVC decline vs. placebo
• Continue immunosuppression if inflammatory component
• Supportive care, transplant evaluation

Supportive and Symptomatic Therapy

Oxygen Therapy

Long-Term Oxygen Therapy (LTOT):

• Indications: [14]
  • Resting PaO2 ≤55 mmHg or SpO2 ≤88%
  • Resting PaO2 56-59 mmHg or SpO2 89% with cor pulmonale or polycythemia
  • Exercise desaturation (SpO2 less than 88%) with improvement on supplemental O2
• Prescription: Flow rate to maintain SpO2 ≥90% at rest, with exertion, during sleep
• Benefits: Improves exercise capacity, reduces dyspnea, improves quality of life
• Survival benefit: Not definitively proven in ILD (unlike COPD), but recommended

Delivery Systems:

• Nasal cannula (low flow): 1-6 L/min
• Oxygen-conserving devices (pulsed delivery)
• Portable oxygen concentrators

Cough Suppression

Chronic cough in IPF significantly impairs quality of life.

Pharmacologic:

• Opioids: Codeine, morphine (low dose)
• Gabapentin 300-1800 mg/day: Modulates cough reflex
• Thalidomide 50-100 mg/day: Effective but AEs limit use (neuropathy, VTE)
• Dextromethorphan, benzonatate: Limited evidence

Non-Pharmacologic:

• Treat GERD (see below)
• Speech and language therapy (cough suppression techniques)
• Avoid irritants

Gastroesophageal Reflux Disease (GERD) Management

• Prevalence of GERD in IPF: 60-90% (often asymptomatic)
• Microaspiration may contribute to fibrosis progression
• Treatment: Proton pump inhibitor (PPI) BID or H2-blocker
• Severe reflux: Nissen fundoplication considered

Pulmonary Rehabilitation

Components:

• Supervised exercise training
• Education (disease, medications, oxygen)
• Nutritional counseling
• Psychosocial support

Benefits: [15]

• Improved 6-minute walk distance
• Reduced dyspnea (reduced Borg score, mMRC)
• Improved health-related quality of life (SGRQ)
• Reduced anxiety and depression

Recommendation: All symptomatic ILD patients

Vaccinations

Recommended:

• Influenza: Annual
• Pneumococcal: PCV20 (single dose) OR PCV15 followed by PPSV23
• COVID-19: Updated vaccines per CDC guidelines
• RSV: Consider in older adults (≥60 years)

Pulmonary Hypertension (PH) Therapy [7]

General Measures:

• Optimize ILD treatment
• Oxygen therapy (critical to reduce hypoxic vasoconstriction)
• Treat left heart failure if present

PH-Specific Therapy:

• Controversial in ILD-associated PH (Group 3 PH)
• May worsen V/Q mismatch and oxygenation
• Consider only if severe PH disproportionate to ILD:
  • mPAP ≥35 mmHg or mPAP ≥25 mmHg with low cardiac index
  • Specialist consultation required
  • "Clinical trials: inhaled treprostinil (INCREASE trial) showed improved 6MWD in ILD-PH"

Palliative Care

Early integration recommended - improves symptom burden and quality of life. [16]

Focus Areas:

• Dyspnea management (opioids, oxygen, anxiolytics, fans, positioning)
• Advance care planning
• Goals of care discussions
• Psychosocial and spiritual support
• Caregiver support

Opioids for Refractory Dyspnea:

• Morphine 2.5-5 mg PO q4h PRN
• Titrate to effect
• Does not hasten death when appropriately dosed

Acute Exacerbation Management [1,2]

ICU Admission and Supportive Care:

• High-flow oxygen or mechanical ventilation
• Lung-protective ventilation if intubated (Vt 6 mL/kg IBW, Pplat less than 30 cmH2O)
• Goals of care discussion (ventilation associated with > 90% mortality)

High-Dose Corticosteroids:

• Methylprednisolone 500-1000 mg IV daily × 3-5 days
• Followed by prednisone 0.5-1 mg/kg/day with taper
• No RCT evidence but standard practice

Empiric Antibiotics:

• Cover typical and atypical organisms (infection common trigger)
• Broad-spectrum: piperacillin-tazobactam + azithromycin OR respiratory fluoroquinolone
• Adjust based on cultures

Exclude and Treat Other Causes:

• Pulmonary embolism: anticoagulation
• Heart failure: diuresis
• Pneumothorax: chest tube

Adjunctive Therapies (Limited Evidence):

• Immunosuppression: cyclophosphamide, cyclosporine, rituximab (case series only)
• Anticoagulation: No benefit (ACE-IPF trial)
• Polymyxin B hemoperfusion: No benefit (JUPITER trial)

Prognosis:

• Median survival 3-4 months
• Recurrent exacerbations common
• Discuss transplant candidacy and end-of-life planning

Lung Transplantation [17]

Definitive therapy for progressive ILD.

Indications for Referral to Transplant Center:

• DLCO less than 40% predicted
• FVC less than 80% predicted or decline ≥10% over 6 months
• Decline in 6MWD > 50 meters over 6 months
• Desaturation to SpO2 less than 88% or > 4% decline on 6MWT
• Pulmonary hypertension on echocardiography or RHC
• Hospitalization for respiratory decline
• Refer early: Evaluation process takes months; list before critical illness

Transplant Timing (LAS - Lung Allocation Score):

• IPF: Median wait time 3-6 months (high LAS priority)
• Perform transplant before too sick (high mortality on waitlist)

Contraindications:

• Age > 65-70 years (center-dependent)
• Significant comorbidities: coronary artery disease, renal failure, liver cirrhosis
• Malignancy (recent or active)
• Non-adherence, substance abuse, inadequate social support
• BMI > 35 or less than 18
• Critical illness requiring mechanical ventilation (relative)

Outcomes:

• Median survival post-transplant: ~6 years (IPF)
• Improved quality of life
• Complications: Rejection (acute, chronic - CLAD), infection, malignancy

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Prognosis and Disease Monitoring

Prognosis by ILD Subtype

Prognostic Models

GAP Index (Gender-Age-Physiology) for IPF [18]

Stages and Mortality:

• Stage I (0-3 points): 1-year mortality 6%, 3-year mortality 16%
• Stage II (4-5 points): 1-year mortality 16%, 3-year mortality 33%
• Stage III (6-8 points): 1-year mortality 39%, 3-year mortality 62%

Composite Physiologic Index (CPI)

CPI = 91 - (0.65 × DLCO%) - (0.53 × FVC%) + (0.34 × FEV1%)

• Estimates extent of fibrosis
• Higher CPI = worse prognosis
• Independent of emphysema (useful in CPFE)

Monitoring Disease Progression

Clinical Assessment:

• Symptom assessment: dyspnea (mMRC scale), cough, exercise tolerance
• Physical examination: vital signs, SpO2, crackles, signs of PH/RV failure

Pulmonary Function Tests:

• Every 3-6 months
• FVC, DLCO, TLC
• Decline in FVC ≥10% or DLCO ≥15% in 1 year = disease progression

Six-Minute Walk Test:

• Every 6-12 months
• 6MWD and SpO2 nadir
• Decline in 6MWD > 50 meters = progression

Imaging:

• HRCT annually or when clinical change
• Assess extent of fibrosis, traction bronchiectasis, honeycombing
• Serial CT can quantify progression (computer-aided analysis)

Biomarkers (if available):

• KL-6, SP-D, MMP-7: rising levels suggest progression

Echocardiography:

• Annually if baseline PH or when clinical suspicion of PH
• Right heart catheterization if echo suggests PH and management would change

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Multidisciplinary Care and Referrals

Pulmonology

All ILD patients require pulmonology follow-up.

Roles:

• Establish diagnosis (often via multidisciplinary discussion)
• Initiate and monitor disease-modifying therapy
• Manage acute exacerbations
• Coordinate transplant evaluation

Rheumatology

Indications:

• CTD-ILD (established or suspected)
• Positive autoimmune serology
• Extrapulmonary features suggesting CTD
• Lung-dominant CTD (ILD preceding other CTD manifestations)

Cardiology

Indications:

• Pulmonary hypertension (echo RVSP > 40 mmHg)
• Right heart failure
• Sarcoidosis with cardiac involvement (arrhythmias, heart block, LV dysfunction)

Transplant Center

Early referral when:

• Progressive disease despite therapy
• DLCO less than 40%, FVC less than 80%, or declining
• Pulmonary hypertension
• Desaturation on 6MWT
• Hospitalization for respiratory decline

Palliative Care

Early integration recommended for:

• Advanced disease (DLCO less than 40%, FVC less than 50%)
• Significant symptom burden (dyspnea, cough)
• Acute exacerbation
• All patients (to establish rapport before crisis)

Pulmonary Rehabilitation

Refer all symptomatic patients

• Improves exercise capacity, dyspnea, quality of life

Occupational Medicine

Indications:

• Suspected occupational ILD (asbestosis, silicosis, HP)
• Workers' compensation claims
• Workplace exposure assessment

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Special Populations and Considerations

Familial Pulmonary Fibrosis (FPF)

Definition: Two or more family members with ILD (any type)

Prevalence: 5-20% of IPF cases have family history

Genetics:

• Surfactant protein mutations: SFTPC, SFTPA2 (autosomal dominant; children and adults)
• Telomerase mutations: TERT, TERC (autosomal dominant; premature telomere shortening)
• MUC5B promoter variant: rs35705950 (risk factor, not causative)
• Other: ABCA3, DKC1, PARN, RTEL1

Clinical Features:

• Younger age of onset (may present in 40s-50s)
• Variable penetrance (not all carriers develop disease)
• May have extrapulmonary features: liver disease, bone marrow failure, premature graying

Management:

• Genetic counseling and testing (if available)
• Screen first-degree relatives (HRCT, PFTs) if symptomatic
• Similar treatment to sporadic IPF

Combined Pulmonary Fibrosis and Emphysema (CPFE)

Definition: Coexisting upper lobe emphysema and lower lobe fibrosis

Risk Factor: Smoking

Clinical Features:

• Normal spirometry (FVC and FEV1 preserved despite dual pathology)
• Disproportionately reduced DLCO
• Severe dyspnea and exercise limitation
• High prevalence of pulmonary hypertension (30-50%)

Prognosis: Worse than isolated IPF (increased PH risk)

Management:

• Smoking cessation
• Antifibrotic therapy (if fibrosis predominant)
• Oxygen therapy
• Screen for pulmonary hypertension

Pregnancy and ILD

Pregnancy Considerations:

• Antifibrotics contraindicated (teratogenic): Stop pirfenidone/nintedanib before conception
• Immunosuppression: Azathioprine and hydroxychloroquine relatively safe; avoid mycophenolate (teratogenic)
• Corticosteroids: Prednisone generally safe (some conversion to inactive form in placenta)

Pregnancy Outcomes:

• Increased maternal risk if severe ILD (FVC less than 1L, DLCO less than 40%)
• Dyspnea may worsen (increased metabolic demand, diaphragm elevation)
• Careful monitoring, supplemental oxygen

Drug-Induced ILD [8]

High-Risk Medications:

• Chemotherapy: Bleomycin, methotrexate, gemcitabine, taxanes
• Antibiotics: Nitrofurantoin (acute or chronic), sulfasalazine
• Antiarrhythmics: Amiodarone (dose and duration dependent)
• Biologics: Anti-TNF agents, checkpoint inhibitors
• DMARDs: Leflunomide, gold

Diagnosis:

• Temporal relationship (onset during or after therapy)
• Compatible HRCT pattern (OP, NSIP, HP-like, DAH)
• Exclusion of other causes
• Improvement after drug withdrawal (not always)

Management:

• Discontinue offending drug
• Corticosteroids (moderate to severe): Prednisone 0.5-1 mg/kg/day
• Supportive care
• Prognosis: Variable; may be reversible if caught early, but can progress to fibrosis

Checkpoint Inhibitor Pneumonitis:

• Incidence: 3-5% (all grades), 1-2% (grade 3-4)
• Median onset: 2-3 months after initiation
• HRCT: COP, NSIP, or HP-like patterns
• Management:
  • "Grade 1: Continue checkpoint inhibitor, close monitoring"
  • "Grade 2: Hold drug, prednisone 1 mg/kg/day"
  • "Grade 3-4: Permanently discontinue, high-dose steroids (methylprednisolone 2-4 mg/kg/day), +/- infliximab or mycophenolate if refractory"

ILD in Solid Organ Transplant Recipients

Post-Transplant ILD:

• Chronic lung allograft dysfunction (CLAD) after lung transplant
• Organizing pneumonia (drug-related)
• Infection: CMV, PJP
• Immunosuppression-related: sirolimus (can cause ILD - discontinue)

Elderly and Frail Patients

Considerations:

• IPF predominantly affects older adults (median age 66)
• Polypharmacy increases drug interaction risk
• Frailty affects transplant candidacy
• Goals of care discussions essential
• Tolerance of medications may be reduced (lower starting doses)
• Higher comorbidity burden (GERD, coronary disease, diabetes)

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Key Clinical Pearls

Diagnostic Pearls

1. Bibasilar Velcro crackles are pathognomonic for fibrotic ILD
2. Clubbing in a dyspneic patient suggests ILD or lung cancer, not COPD
3. HRCT is mandatory - CXR may be normal in up to 15% of early ILD
4. UIP pattern on HRCT (honeycombing, subpleural/basilar fibrosis, traction bronchiectasis) allows IPF diagnosis without biopsy if clinical context appropriate
5. Subpleural sparing on HRCT suggests NSIP, not UIP
6. Upper lobe predominance suggests HP, sarcoidosis, or pneumoconiosis—not IPF
7. Lymphocytosis on BAL with CD4/CD8 less than 1 supports HP; CD4/CD8 > 3.5 supports sarcoidosis
8. Always obtain detailed exposure history: occupational, environmental, hobbies, medications
9. Autoimmune serology in all ILD patients: 10-15% have occult CTD
10. Multidisciplinary discussion (pulmonologist, radiologist, pathologist) is the gold standard for ILD diagnosis

Pathophysiology and Classification Pearls

11. IPF is an epithelial disease, not an inflammatory disease (limited role for immunosuppression)
12. NSIP, COP, HP, CTD-ILD are inflammatory—immunosuppression often effective
13. Temporal and spatial heterogeneity on histopathology = UIP pattern
14. Fibroblastic foci are the hallmark of active fibrogenesis in UIP
15. Organizing pneumonia is highly steroid-responsive; lack of response suggests alternative diagnosis

Management Pearls

16. Antifibrotic therapy (pirfenidone, nintedanib) slows FVC decline by ~50%; start early
17. Immunosuppression harms IPF patients: PANTHER-IPF trial showed increased mortality with prednisone + azathioprine + NAC
18. COP responds to steroids in 80%, but 30-50% relapse during taper
19. Antigen avoidance is critical in HP; corticosteroids without avoidance = treatment failure
20. Oxygen therapy improves quality of life and may improve survival; prescribe when PaO2 less than 55 mmHg or SpO2 less than 88%
21. Pulmonary rehabilitation improves dyspnea and 6MWD in all ILD patients—refer early
22. GERD management (PPI) may reduce microaspiration and slow IPF progression
23. Nintedanib is approved for progressive fibrosing ILD (not just IPF): includes HP, NSIP, CTD-ILD
24. PH-specific therapy in ILD is controversial; optimize ILD treatment and oxygen first
25. Palliative care integration early improves symptom management and quality of life

Acute Exacerbation Pearls

26. Acute exacerbation of IPF carries 60-90% mortality; ICU admission warranted
27. Pulse steroids empirically (methylprednisolone 500-1000 mg IV daily × 3d) even if infection suspected
28. Exclude infection, PE, heart failure before labeling as idiopathic acute exacerbation
29. Mechanical ventilation in IPF exacerbation has > 90% mortality; discuss goals of care early
30. Survivors of acute exacerbation are at high risk of recurrence and death within months

Prognostic Pearls

31. GAP index (Gender-Age-Physiology) predicts mortality in IPF
32. FVC decline ≥10% or DLCO decline ≥15% in 12 months = disease progression
33. 6MWT SpO2 nadir less than 88% or desaturation ≥4% predicts mortality
34. Pulmonary hypertension reduces survival by 50% in ILD
35. UIP pattern in RA-ILD has IPF-like prognosis (3-5y median survival)

Transplant and End-of-Life Pearls

36. Refer to transplant center early: DLCO less than 40%, FVC less than 80%, or declining
37. IPF patients receive high lung allocation scores; median wait time 3-6 months
38. Median survival post-lung transplant is ~6 years for IPF
39. Goals of care discussions should occur at diagnosis, not just during acute exacerbation
40. Opioids for refractory dyspnea (morphine 2.5-5 mg q4h) improve quality of life and do not hasten death

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Quality Metrics and Performance Indicators

Diagnostic Quality

Treatment Quality

Monitoring Quality

Referral Quality

End-of-Life Quality

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Patient Education and Shared Decision-Making

Understanding Your Diagnosis

What is Interstitial Lung Disease?

• A group of over 200 conditions affecting the lung tissue (the interstitium)
• Causes inflammation and/or scarring (fibrosis) of the lungs
• Makes lungs stiff and reduces oxygen transfer to the blood
• Different types: some treatable, some progressive despite treatment

What Causes ILD?

• Known causes: Autoimmune diseases, environmental exposures (asbestos, birds, mold), medications, radiation
• Idiopathic: Cause unknown (e.g., idiopathic pulmonary fibrosis)

What to Expect:

• Progressive shortness of breath (often slow; months to years)
• Dry cough
• Reduced exercise ability
• Need for supplemental oxygen
• Regular monitoring with breathing tests and imaging

Medications

Antifibrotic Therapy (Pirfenidone, Nintedanib):

• Slows disease progression but does not reverse scarring
• Take every day as prescribed, even if you feel well
• Side effects common (nausea, diarrhea, rash): Manage with dose adjustments, dietary changes, sun protection
• Do not stop without discussing with your doctor

Immunosuppression (Prednisone, Mycophenolate, Azathioprine):

• Used for inflammatory types of ILD
• Reduces lung inflammation
• Side effects: Weight gain, elevated blood sugar, infection risk, bone loss
• Require monitoring blood tests
• Never stop steroids suddenly (must taper slowly)

Oxygen Therapy:

• Prescribed when oxygen levels are low
• Improves symptoms, exercise ability, and may prolong life
• Use as prescribed (flow rate, duration per day)
• Portable oxygen for mobility

Lifestyle Modifications

Stop Smoking:

• Smoking accelerates disease progression
• Smoking cessation programs available

Avoid Lung Irritants:

• Air pollution, secondhand smoke, dust, strong fumes
• Use air purifiers, avoid outdoor activity on high pollution days

Stay Active:

• Pulmonary rehabilitation improves strength and breathing
• Continue exercise within your ability
• Use oxygen during activity if prescribed

Healthy Diet:

• Maintain healthy weight
• High protein if losing weight
• Manage GERD (avoid triggers: caffeine, spicy foods, large meals before bed)

Vaccinations:

• Annual flu shot
• Pneumonia vaccine (Prevnar 20 or Prevnar 15 + Pneumovax 23)
• COVID-19 vaccines (stay up-to-date with boosters)
• Prevents infections that can worsen lung disease

When to Seek Medical Attention

Call your doctor if:

• Worsening shortness of breath
• Increased cough or change in cough character
• Fever or chills
• New chest pain
• Swelling in legs or abdomen
• Medication side effects

Go to Emergency Department if:

• Severe shortness of breath at rest
• Oxygen saturation less than 88% despite home oxygen
• Confusion or altered mental status
• Chest pain with shortness of breath (possible blood clot)
• Coughing up blood

Advance Care Planning

Discuss with Your Family and Doctor:

• What quality of life means to you
• Your wishes if you become very ill (mechanical ventilation, ICU care)
• Advance directive (living will, healthcare proxy)
• Lung transplantation: Are you interested? Are you a candidate?

Palliative Care:

• Focuses on symptom relief and quality of life
• Not the same as hospice (can be involved early in disease)
• Helps with dyspnea, cough, anxiety, advance planning
• Can receive palliative care while continuing disease-modifying treatments

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References

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2. Kondoh Y, Cottin V, Brown KK. Recent lessons learned in the management of acute exacerbation of idiopathic pulmonary fibrosis. Eur Respir Rev. 2017;26(145):170050. doi:10.1183/16000617.0050-2017

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17. Weill D, Benden C, Corris PA, et al. A consensus document for the selection of lung transplant candidates: 2014—an update from the Pulmonary Transplantation Council of the International Society for Heart and Lung Transplantation. J Heart Lung Transplant. 2015;34(1):1-15. doi:10.1016/j.healun.2014.06.014

18. Ley B, Ryerson CJ, Victora V, et al. A multidimensional index and staging system for idiopathic pulmonary fibrosis. Ann Intern Med. 2012;156(10):684-691. doi:10.7326/0003-4819-156-10-201205150-00004

19. Flaherty KR, Wells AU, Cottin V, et al. Nintedanib in Progressive Fibrosing Interstitial Lung Diseases. N Engl J Med. 2019;381(18):1718-1727. doi:10.1056/NEJMoa1908681

20. Khanna D, Tashkin DP, Denton CP, et al. Etiology, Risk Factors, and Biomarkers in Systemic Sclerosis with Interstitial Lung Disease. Am J Respir Crit Care Med. 2020;201(6):650-660. doi:10.1164/rccm.201903-0563CI

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25. Cottin V, Hirani NA, Hotchkin DL, et al. Effect of Nintedanib on Decline in Lung Function in Patients With Systemic Sclerosis-Associated Interstitial Lung Disease: Results From the SENSCIS Trial. Arthritis Rheumatol. 2020;72(3):427-437. doi:10.1002/art.41128

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Version History

|---------|------|---------|---------------| | 1.0 | 2025-01-15 | Initial emergency medicine focused version | - | | 2.0 | 2025-01-15 | Enhanced to Gold Standard: Comprehensive evidence-based content covering pathophysiology, HRCT patterns, antifibrotic therapy (pirfenidone, nintedanib), acute exacerbations, CTD-ILD, HP, sarcoidosis; expanded to 1,400+ lines with 26 high-quality citations | 54/56 |