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Interstitial Lung Disease¶

Chapter 304 | Interstitial Lung Disease | Part 7 – Respiratory Disorders · Part 7 – Respiratory Disorders · Chapter 304

Key Clinical Points¶

Diagnosis of ILD requires a multidisciplinary approach combining clinical data, laboratory studies, pulmonary function testing (PFT), imaging (HRCT), and histopathology.
Idiopathic Pulmonary Fibrosis (IPF) is the most common ILD of unknown cause; characterized by a UIP pattern on HRCT (subpleural reticular changes, honeyctombing, traction bronchiectasis).
Antifibrotic therapy (pirfenidone, nintedanib) slows lung function decline in IPF.
Nonspecific Interstitial Pneumonia (NSIP) has a better prognosis than IPF (>80% 5-year survival).
Smoking is specifically associated with Respiratory Bronchiolitis–ILD and Desquamative Interstitial Pneumonia (DIP).
Systemic Sclerosis (SSc) is the most common connective tissue disease associated with ILD.
Acute Interstitial Pneumonia (AIP) is rare, often fatal, and characterized by acute respiratory distress.
Lung transplantation remains the standard of care for advanced and rapidly progressive ILDs.
Genetic markers MUC5B (promoter variant) and TERT (telomere length) are key determinants in pulmonary fibrosis.
No single piece of data (e.g., a biopsy showing UIP pattern) is sufficient to confirm a diagnosis alone; multidisciplinary review is essential.

DEFINITION & OVERVIEW¶

• Definition: Interstitial lung diseases (ILDs) are a large group (>200) of heterogeneous conditions affecting the lung parenchyma with varying degrees of inflammation and fibrosis. • Pathophysiology: ◦ Primary site: Remodeling of the interstitial space (between epithelium and endothelium). ◦ Key cellular components: Alveolar epithelium and endothelial cells (including both airways and vessels) play prominent roles in pathogenesis. • Diagnostic Principle: No single piece of data confers a diagnosis alone. A multidisciplinary approach involving pulmonologists, rheumatologists, radiologists, and pathologists is recommended to integrate clinical data, lab studies, PFTs, imaging, and histopathology.

Classification of Interstitial Lung Disease (Flowchart 1)¶

The following decision pathway outlines the classification of ILD based on etiology:

Step 1: Is the cause of the interstitial lung disease known? • Yes → Known Cause ◦ Path A: Exposure ◦ Occupational → [Asbestosis, Silicosis] ◦ Treatment related → [Radiation, Methotrexate, Amiodarone, Nitrofurantoin, Chemotherapeutics] ◦ Path B: Systemic disease ◦ Connective tissue disease → [Rheumatoid arthritis, Scleroderma, Polymyositis, Dermatomyositis] ◦ Path C: Granulomatous/Vasculitic ◦ Granulomatous disease with vasculitis → [Granulomatosis with polyangiitis, Churg-Strauss] ◦ Granulomatous lung disease → [Sarcoidosis, Hypensensitivity pneumonia] • No → Unknown Cause ◦ Path D: Idiopathic interstitial pneumonias ◦ Idiopathic pulmonary fibrosis ◦ Other Idiopathic → [Nonspecific interstitial pneumonia (NSIP), Respiratory bronchiolitis—associated ILD, Desquamative interstitial pneumonia (DIP), Cryptogenic organizing pneumonia (COP), Acute interstitial pneumonia (AIP), Lymphocytic interstitial pneumonia (LIP)] ◦ Path E: Other ◦ [Lymphangioleiomyosarcoma (LAM), Pulmonary alveolar proteinosis, Langerhans-1 cell histiocytosis (PLCH), Erdheim-Chernoff lymphangioreticulosis]

EPIDEMIOLOGY¶

• Common Forms: IPF, sarcoidosis, and ILDs related to connective tissue diseases (CTDs) are the most common forms. • Age of Onset: ◦ IPF: Typically >60 years; rare in patients <50 years. ◦ Sarcoidosis, CTD-associated ILD, LAM, and PLCH: Typically 20–40 years. • Sex Distribution: ◦ LAM (and tuberous sclerosis): Frequently diagnosed in young women. ◦ CTD-associated ILDs: More common in women (except RA-associated ILD, which is more common in men). ◦ IPF and occupational/exposure-related ILDs: More common in men.

Prevalence¶

• IPF: ◦ Prevalence: 50–200 per 100,000. ◦ Clinical Profile: Typically diagnosed in the 5th or 6th decade; associated with smoking/environmental exposure. ◦ Prognosis: 50% 3- to 5-year mortality.

Risk Factors¶

• Family History: Strong risk factor for IPF; up to 20% of pulmonary fibrosis cases may be familial. ◦ Genetic Markers: ◦ MUC5B: Promoter variant associated with both familial and idiopathic pulmonary fibrosis. ◦ TERT: Variants influencing telomere length, associated with both familial and idiopathic forms.

ETIOLOGY & PATHOPHYSIOLOGY¶

• Classification Overlap: Genetic studies challenge the 'known' vs. 'unknown' distinction; many 'unknown' cases (e.g., IPF, LAM) have significant genetic underpinnings. • Pathogenesis: ◦ Primary site: Remodeling of the interstitial space. ◦ Key cells: Alveolar epithelium and endothelial cells (airways/vessels). • Treatment Variability: ◦ Management varies significantly by disorder; treatments effective for some ILDs may be harmful to others. ◦ Range: From immune modulators to antifibrotic medications. ◦ Standard of Care: Lung transplantation for advanced and rapidly progressive ILDs.

CLINICAL FEATURES¶

• Common Presentations: Progressive exertion-related dyspnea or persistent dry cough. • Non-respiratory Indicators: ◦ Systemic Sclerosis → skin thickening. ◦ Rheumatoid Arthritis → ulnar deviation of the fingers. • Incidental Findings: Identified via abnormal PFTs, CXR, CT (chest/abdomen), or PET scans.

Symptoms¶

• Dyspnea: Most common; often exertional. Some patients with extensive disease may not report it. ◦ Cough: Common; dry cough is prominent in IPF. → Hemoptysis → Rare; suggests DAH (e.g., Goodpasture's), GPA, or LAM. → Hemoptysis → Also possible with secondary infection in patients with traction bronchiectasis or those on immunosuppression. ◦ Fatigue: Common to all ILDs. ◦ Chest Pain: Rare; uncommon even in sarcoidosis.

Physical Examination¶

• Crackles (Rales): End-inspiratory fine crackles at lung bases; early sign in IPF; non-specific. ◦ Wheezing: Uncommon; seen in sarcoidosis, HP, and eosinophilic GPA. ◦ Advanced Disease Signs: Cyanosis, digital clubbing, and cor pulmonale.

History¶

• Age: → >60 years → High probability of IPF. → 20–40 years → Suggests sarcoidosis, CTD-ILD, LAM, or PLCH. ◦ Duration: → Acute (days/weeks) → Unusual; may be misdiagnosed as pneumonia, COPD exacerbation, or heart failure. (Exceptions: eosinophilic pneumonia, AIP, HP, GPA). → Subacute (weeks/months) → Suggests sarcoidosis, CTD-ILD, drug-induced ILD, or COP. ◦ Medications: → Risk factors: Methotrexate, azathioprine, rituximab, and TNF-α blockers. → Specific classes: Antibiotics (nitrofurantoin), antiarrhythmics (amiodarone), antineoplastic agents (bleomycin). ◦ Social/Environmental: → Smoking → Associated with RB-ILD and DIP. → Occupational → Asbestosis, Silicosis; Bird exposure (HP).

DIFFERENTIAL DIAGNOSIS¶

• Multidisciplinary Approach: Essential to integrate pulmonology, rheumatology, radiology, and pathology. • Key Diagnostic Challenge: No single piece of data (e.g., a biopsy showing UIP) is sufficient for diagnosis alone as it can occur in both IPF and CTD-associated ILD.

Common vs. Rare ILDs¶

• Common: IPF, sarcoidosis, CTD-associated ILD. ◦ Age 20–40: Sarcoidosis, CTD-ILD, LAM, PLCH. • Rare: LAM, PLCH. ◦ Granulomatous/Vasculitic: Sarcoidosis (known), HP (known), GPA, Churg-Strauss.

INVESTIGATIONS & DIAGNOSIS¶

Pulmonary Function Tests (PFTs): → Identify restrictive deficit: \downarrowTLC and symmetrically reduced FEV1/FVC. → Assess DLCO: Often reduced; may precede volume loss; helps characterize extent. → Airway involvement: Reduced FEV1/FVC ratio (atypical) seen in sarcoidosis, HP, or LAM.
Chest Imaging: → CXR: Initial indicator (e.g., hilar lymphadenopathy for sarcoidosis; basilar reticular pattern for IPF). → HRCT: Standard of care; used to define extent, identify honeycombing, and select biopsy sites.
Lung Biopsy: → Bronchoscopy: Useful for DAH (lavage), granulomatous disease (transbronchial/lymph node), or specific features (eosinophilia, fat globules). → Surgical Lung Biopsy (VATS): Higher yield; preferred before treatment; higher risk in IPF and acute presentations.
Laboratory Studies: → Primarily used to identify underlying CTD (e.g., anti-CCP for RA).

Table 304-1: Clinical Comparison of Common ILDs¶

• IPF: 50% 3- to 5-year mortality; UIP pattern (reticular changes, honeycombing). • NSIP: 18% 5-year mortality; ground-glass and reticular patterns. • RB-ILD: 25% 7-year mortality; strong link to smoking. • SSc-associated: 20–30% 10-year mortality; includes skin/joint findings. • Sarcoidosis: Noncaseating granulomas.

MANAGEMENT & TREATMENT¶

• General Principles: ◦ Treatment varies by disease; some therapies are harmful in specific contexts. ◦ Standard of Care: Lung transplantation for advanced or rapidly progressive ILDs. ◦ Supportive Care: Physical therapy and supplemental oxygen (improve exercise tolerance, reduce pulmonary hypertension).

Specific Management Plans: 1. Idiopathic Pulmonary Fibrosis (IPF): → Antifibrotic therapy: Pirfenidone or nintedanib (slow lung function decline; may improve survival). 2. Nonspecific Interstitial Pneumonia (NSIP): → Treatment includes immune modulators. 3. Smoking-Related ILD: → Primary action: Smoking cessation programs. 4. Cryptogenic Organizing Pneumonia (COP): → Management varies based on clinical context. 5. Systemic Sclerosis (SSc) Associated ILD: → Treatment includes immune modulators.

Clinical Summary of Outcomes¶

• IPF: 50% mortality in 3- to 5-year period. • NSIP: >80% 5-year survival (18% mortality). • RB-ILD: 25% 7-year mortality. • SSc-associated: 20–30% 10-year mortality.

PROGNOSIS & COMPLICATIONS¶

• IPF Prognosis: 50% mortality within 3- to 5-year period. • NSIP Prognosis: >80% 5-year survival (18% mortality). • RB-ILD Prognosis: 25% 7-year mortality. • SSc-associated ILD: 20–30% 10-year mortality. • Complications: Pulmonary hypertension, reduced exercise tolerance, and rapid progression requiring transplantation.

SPECIAL CONSIDERATIONS¶

• Genetic Factors: → MUC5B promoter variant → risk for pulmonary fibrosis. → TERT variants → influence telomere length; associated with both familial and idiopathic cases. • Smoking-Related ILD: → Respiratory Bronchiolitis (RB) and Desquamative Interstitial Pneumonia (DIP) are specifically linked to smoking history.

Clinical Pearls¶

• Multidisciplinary Approach: Essential for diagnosis due to overlapping features of ILDs. • Imaging Standard: HRCT is the primary tool for defining extent and identifying honeycombing (UIP pattern). • Antifibrotic Therapy: Pirfenidone and nintedanib are the standard for slowing decline in IPF; avoid steroids in these patients. • Clinical Clues: → Age >60 + Honeycombing → High suspicion of IPF. → Younger age (20-40) + Granulomas → Sarcoidosis. → Skin thickening/Joint issues → Systemic Sclerosis. • Rapid Progression: Lung transplantation is the definitive management for advanced or rapidly progressive cases.

Reference Tables¶

TABLE 304-1 Common Interstitial Lung Disease (ILD) Findings Clinical symptoms¶

Harrison's 22e, p.2260

	IPF	NONSPECIFIC INTERSTITIAL PNEUMONIA	RESPIRATORY BRONCHIOLITIS– ASSOCIATED ILD	SYSTEMIC SCLEROSIS– ASSOCIATED ILD	SARCOIDOSIS
Clinical symptoms	Gradual onset of SOB, dry cough. More common in older adults.	Subacute onset of SOB, dry cough. Frequently associated with other conditions.	Can be asymptomatic, or have SOB and cough.	Gradual onset of SOB, dry cough. Fatigue, tightening of skin, exaggerated cold response, reflux, and difficulty swallowing.	Can be asymptomatic, or have SOB and cough. Can also have fatigue, palpitations, and eye, skin, and joint findings.
	Frequent rales at lung bases; digital clubbing is common.	Frequent rales. Clubbing is less common.	Rales common. Clubbing is rare.	Can have rales in isolation. Also skin thickening, joint swelling, and telangiectasias.
Exposures	Idiopathic but many exposed to smoke. Genetic findings may explain more than one-third of the risk of the disease.	Can be idiopathic but should prompt consideration for associated conditions.	Strong association with smoking.	Mostly unknown; some debate about solvent and silicate exposures.	Mostly unknown, although silicate dusts thought to play a role in some cases.
	Bilateral subpleural reticular changes most prominent in lower, posterior lung zones. Traction bronchiectasis and honeycombing common. Classic usual interstitial pneumonia (UIP) pattern is considered diagnostic.	Peripheral subpleural ground-glass and reticular patterns. Traction bronchiectasis is common, but honeycombing is rare. HRCT not diagnostic.	Diffuse patchy centrilobular ground glass nodules.	Can have UIP or nonspecific interstitial pneumonia (NSIP) patterns, also dilated esophagus, occasional mediastinal calcifications, and pulmonary vascular enlargement.
Histopathology	UIP pattern including fibroblastic foci, temporal and spatial heterogeneity, honeycombing.	Cellular or fibrotic pattern of NSIP. More uniform than a UIP pattern.	Respiratory bronchiolitis with adjacent inflammatory and fibrosing changes. Pigment-laden macrophages.	Both UIP or NSIP patterns can occur.	Noncaseating granulomas.
	50% 3- to 5-year mortality.	18% 5-year mortality.	25% 7-year mortality.	20–30% 10-year mortality.