Interstitial Lung Diseases (ILD) - NEET PG

Overview

• Progressive exertional dyspnea
• Persistent dry cough
• Fine end-inspiratory crackles (Velcro crackles) at lung bases
• Digital clubbing (especially IPF)

Classification (Goldman-Cecil / Harrison's)

1. Idiopathic Interstitial Pneumonias (IIPs)

2. ILD Associated with Connective Tissue Disease

• Systemic sclerosis (SSc), RA, SLE, Dermatomyositis/Polymyositis, Sjögren's syndrome, Mixed CTD, Ankylosing spondylitis

3. Hypersensitivity Pneumonitis

• Farmer's lung, Bird fancier's lung, Humidifier lung, etc.

4. Drug-Induced ILD

• Bleomycin, Amiodarone, Methotrexate, Nitrofurantoin, Cyclophosphamide, Nitrosoureas, Checkpoint inhibitors (nivolumab, pembrolizumab)

5. Alveolar Filling Disorders

• Goodpasture syndrome, Pulmonary alveolar proteinosis, Pulmonary hemosiderosis, Chronic eosinophilic pneumonia

6. ILD with Pulmonary Vasculitis

• Granulomatosis with polyangiitis (Wegener's), Churg-Strauss syndrome, Pulmonary capillaritis

7. Other Specific ILDs

• Sarcoidosis, Langerhans cell histiocytosis, Lymphangioleiomyomatosis (LAM)

Pulmonary Function Tests in ILD

• ↓ FVC, ↓ TLC, ↓ DLCO
• FEV1/FVC ratio: normal or increased (unlike obstructive)
• Exception: Sarcoidosis may show obstructive pattern in significant proportion of patients

Idiopathic Pulmonary Fibrosis (IPF) ⭐ High-Yield

Key Facts

• Most common ILD of unknown cause
• Prevalence: 50-200 per 100,000 (increases with age)
• Predominantly in men, >50 years, often smokers
• Poor prognosis: 50% 3-5 year survival

Pathology

• Histologic pattern: UIP (Usual Interstitial Pneumonia)
• Key features:
  • Patchy interstitial fibrosis
  • Fibroblastic foci (subepithelial collections of myofibroblasts + collagen)
  • Honeycomb lung (cystic spaces)
  • Temporal and spatial heterogeneity (areas of normal lung adjacent to fibrosis)
• Pathogenesis: senescence of alveolar epithelium (telomere shortening) → TGF-β driven fibrosis

HRCT Findings (UIP pattern)

• Peripheral, subpleural, basal-predominant reticulation
• Honeycombing + traction bronchiectasis
• Absence of ground-glass opacities (if prominent → alternate diagnosis)

CT chest showing UIP pattern - peripheral coarse honeycombing (Rheumatology, Elsevier 2022)

Treatment

• Antifibrotic agents (first-line since 2014):
  • Pirfenidone - 267 mg TID orally (anti-inflammatory, antifibrotic, antioxidant)
  • Nintedanib - 150 mg BD orally (tyrosine kinase inhibitor against FGFR, VEGFR, PDGFR)
  • Both slow decline in FVC but do not reverse fibrosis
• Lung transplantation: for advanced/rapidly progressive disease
• Steroids are NOT effective in IPF (key NEET point - steroids can be harmful)

Comparison of Key IIPs (High-Yield Table)

Key NEET Point: COP responds excellently to corticosteroids. IPF does NOT. NSIP may respond to immunosuppression.

Hypersensitivity Pneumonitis (HP / Extrinsic Allergic Alveolitis) ⭐

Pathogenesis

• Immunologically mediated (Type III + Type IV hypersensitivity)
• Caused by inhalation of organic antigens (thermophilic bacteria, fungi, animal proteins)
• BAL: ↑ CD4+ and CD8+ T lymphocytes, proinflammatory chemokines (IL-8, MIP-1α)
• Nonnecrotizing (non-caseating) granulomas in ~2/3 of patients

Common Causes (Memorize for NEET)

Histology

• Acute: Alveolar damage, neutrophil infiltration
• Subacute: Interstitial lymphocytes, plasma cells, macrophages + nonnecrotizing granulomas (centered on bronchioles)
• Chronic: Interstitial fibrosis, honeycombing, obliterative bronchiolitis

Treatment

• Removal of antigen is primary
• Corticosteroids for acute/subacute phase

Sarcoidosis (ILD context) ⭐

• Multisystem disease of unknown etiology
• Hallmark: Noncaseating granulomas (distinguish from TB which is caseating)
• CD4+ Th1 T cells dominate, secreting IFN-γ and IL-2
• Lung involvement: 90% of cases
• Other features: Hilar lymphadenopathy (bilateral), erythema nodosum, uveitis, hypercalcemia
• SACE (Serum ACE) elevated
• PFTs: Can be restrictive, obstructive, or normal (sarcoidosis often has normal FVC at diagnosis, unlike other ILDs)
• Treatment: Corticosteroids

CTD-Associated ILD

Key NEET Point: Scl-70 (anti-topoisomerase I) antibody is associated with increased risk of ILD in SSc.

Pneumoconioses (Inorganic Dust ILDs)

Acute Interstitial Pneumonia (AIP / Hamman-Rich Syndrome)

• Rapidly progressive ILD, often fatal
• Histology: Diffuse Alveolar Damage (DAD) - same as ARDS
• Mimics severe ARDS but idiopathic
• Treatment: Supportive, mechanical ventilation; steroids not clearly effective
• Mortality: Very high

Acute Exacerbations of ILD

• Accelerated phase of injury in any fibrosing ILD; most severe in IPF
• Definition: Acute onset (<30 days) of respiratory distress + new bilateral GGO on background of fibrosis
• Histology: DAD (or organizing pneumonia)
• Mortality: >85%
• Treatment: Supportive; nintedanib may reduce frequency in IPF

Lymphangioleiomyomatosis (LAM) ⭐

• Almost exclusively in young women of reproductive age
• Proliferation of abnormal smooth muscle cells (LAM cells) along lymphatics/airways/vessels
• Associated with tuberous sclerosis
• HRCT: Diffuse thin-walled cysts throughout both lungs (bilateral, uniform distribution)
• Complications: Recurrent pneumothorax, chylous pleural effusion
• PFTs: Obstructive pattern (unlike most other ILDs which are restrictive) - key differentiator
• Treatment: Sirolimus (mTOR inhibitor), lung transplantation

Drug-Induced ILD (Drugs to Remember)

High-Yield NEET PG Summary Points

1. ILD = Restrictive lung disease: ↓FVC, ↓TLC, ↓DLCO, normal FEV1/FVC
2. IPF: UIP pattern, honeycomb + fibroblast foci, temporal heterogeneity, treated with pirfenidone/nintedanib (NOT steroids)
3. COP: Treated with corticosteroids - excellent response
4. NSIP: Best prognosis among fibrosing ILDs; responds to immunosuppression; seen in SSc
5. Farmer's lung: Thermophilic actinomycetes (Type III + IV hypersensitivity)
6. Sarcoidosis: Noncaseating granulomas, bilateral hilar lymphadenopathy, ↑SACE, steroids
7. LAM: Young women, cysts on HRCT, obstructive PFTs, recurrent pneumothorax, sirolimus
8. Asbestos: Mesothelioma, ferruginous bodies, lower lobe fibrosis
9. Silicosis: Eggshell calcification, upper lobe predominance, ↑TB risk
10. AIP (Hamman-Rich): DAD histology, mimics ARDS, very high mortality
11. DIP/RB-ILD: Smoking-related, macrophage-filled alveoli/bronchioles, responds to smoking cessation
12. SSc-ILD: NSIP pattern most common; Scl-70 antibody increases risk

Your INI-CET Study Profile (Applied to All Answers)

• Tables and comparison charts
• Highlighted high-yield points (marked ⭐)
• INI-CET-specific emphasis (conceptual understanding + image-based MCQs)
• Important "AIIMS previously asked" distinctions where relevant

What Makes INI-CET Different from NEET PG

How to Use This Chat

• "Hepatitis B for INI-CET"
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• "Shoulder anatomy"
• "Drugs in pregnancy"
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1. Textbook-sourced (Harrison's, Robbins, Gray's, Goodman & Gilman, etc. from the medical library)
2. INI-CET framed - conceptual depth, image interpretation, recent updates
3. Exam-ready - tables, comparisons, high-yield highlights, and mnemonics where applicable