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Interstitial lung disease (ILD)

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Interstitial lung disease (ILD)

Interstitial lung disease (ILD) is a group of disorders that cause inflammation and/or scarring (fibrosis) of the lung interstitium, leading to stiff lungs and impaired oxygen transfer.

Also called

Diffuse parenchymal lung disease (DPLD)

ICD-10

J84.9

Specialty

Pulmonology

Onset

Chronic

Reviewed

July 2026

On This Page

Overview

Interstitial lung disease (ILD) includes many different diseases that affect the:

  • Lung interstitium
  • Alveoli
  • Small airways
  • Pulmonary blood vessels

Persistent injury may cause:

Inflammation → Fibrosis → Stiff lungs → Reduced oxygen transfer

Patients typically present with progressive exertional dyspnea and a dry cough.

Etiology & Risk Factors

Common Causes

Idiopathic

  • Idiopathic pulmonary fibrosis (IPF)
  • Other idiopathic interstitial pneumonias

Autoimmune Diseases

  • Rheumatoid arthritis
  • Systemic sclerosis
  • Inflammatory myopathies
  • Sjögren syndrome
  • Systemic lupus erythematosus

Occupational & Environmental Exposure

  • Asbestos
  • Silica
  • Coal dust
  • Organic dusts
  • Bird exposure
  • Mold exposure

Drugs

  • Amiodarone
  • Methotrexate
  • Bleomycin
  • Nitrofurantoin

Other Causes For Interstitial lung disease (ILD)

  • Sarcoidosis
  • Hypersensitivity pneumonitis
  • Radiation therapy

Risk Factors

  • Increasing age
  • Cigarette smoking
  • Occupational dust exposure
  • Bird or mold exposure
  • Autoimmune disease
  • Family history of Interstitial lung disease (ILD)
  • Use of pulmonary-toxic medications

Pathophysiology

Flow Chart

Lung injury or abnormal immune response
⬇
Inflammation of the alveoli and interstitium
⬇
Repeated tissue injury
⬇
Abnormal healing response
⬇
Fibroblast activation + Collagen deposition
⬇
Interstitial fibrosis
⬇
Thickened alveolar-capillary membrane
⬇
Stiff lungs + Impaired oxygen diffusion
⬇
Restrictive lung disease + Hypoxemia

Key Concept

Fibrosis reduces lung compliance, making the lungs difficult to expand.

Clinical Presentation

  1. Symptoms

    • Progressive exertional dyspnea
    • Persistent dry cough
    • Fatigue
    • Reduced exercise tolerance
    • Chest discomfort

    Advanced Disease

    • Dyspnea at rest
    • Weight loss
    • Cyanosis

    Signs

    • Fine inspiratory crackles
    • Digital clubbing
    • Tachypnea
    • Reduced oxygen saturation

    Advanced Signs of Interstitial lung disease (ILD)

    • Cyanosis
    • Signs of pulmonary hypertension
    • Signs of right-sided heart failure

History Taking

  • In Interstitial lung disease (ILD), Ask about:

    • Shortness of breath?
    • Is it progressive?
    • Dry cough?
    • When did symptoms start?
    • Occupational exposure?
    • Dust exposure?
    • Asbestos or silica exposure?
    • Bird exposure?
    • Mold exposure?
    • Smoking history?
    • Current and previous medications?
    • Previous radiation therapy?

Physical Examination

Look for:

  • Tachypnea
  • Cyanosis
  • Reduced oxygen saturation
  • Digital clubbing

Chest Examination

  • Fine end-inspiratory crackles
  • Reduced chest expansion in advanced disease

Look for an Underlying Cause for Interstitial lung disease (ILD)

  • Joint swelling or deformity
  • Skin thickening
  • Skin rash
  • Muscle weakness
  • Raynaud phenomenon

Advanced Interstitial lung disease (ILD)

Look for:

    • Raised JVP
    • Peripheral edema
    • Signs of pulmonary hypertension
    • Signs of cor pulmonale

Classification

Interstitial Lung Disease · Classification — ATS/ERS 2013

Idiopathic Interstitial Pneumonias (IIPs)
No identifiable cause; diagnosis by clinical, radiological & histological pattern
Major IIPs
IPFIdiopathic Pulmonary Fibrosis — UIP pattern; worst prognosis
NSIPNon-specific Interstitial Pneumonia — ground-glass; better prognosis
COPCryptogenic Organising Pneumonia — steroid-responsive
AIPAcute Interstitial Pneumonia (Hamman-Rich) — DAD pattern; rapidly fatal
RB-ILDRespiratory Bronchiolitis-ILD — smokers; macrophage accumulation
DIPDesquamative Interstitial Pneumonia — smoking-related; macrophage filling
LIPLymphoid Interstitial Pneumonia — lymphocytic infiltration; Sjögren's association
Rare IIPs
PPFEPleuroparenchymal Fibroelastosis — upper lobe pleural fibrosis
iDIP / iRB-ILDIdiopathic forms in non-smokers (rare)
CTD-associated ILD (CTD-ILD)
ILD secondary to systemic autoimmune disease
RA-ILDRheumatoid Arthritis — UIP or NSIP pattern; most common CTD-ILD
SSc-ILDSystemic Sclerosis (Scleroderma) — NSIP pattern; most common cause of death in SSc
PM/DM-ILDPolymyositis / Dermatomyositis — NSIP or OP pattern; anti-Jo-1 antibody
SLE-ILDSystemic Lupus Erythematosus — less common; pleuritis also frequent
Sjögren's-ILDSjögren Syndrome — LIP or NSIP; cystic lung disease
MCTD-ILDMixed Connective Tissue Disease
IPAFInterstitial Pneumonia with Autoimmune Features — serological or morphological features without full CTD diagnosis
Hypersensitivity Pneumonitis (HP)
Extrinsic allergic alveolitis — inhaled antigen exposure
Acute HP4–8h after exposure; flu-like; reversible
Subacute HPInsidious onset; weeks to months
Chronic HPFibrotic; UIP-like; may not fully reverse
Common antigens: Farmer's lung (Aspergillus/thermophilic bacteria), Bird fancier's lung (avian proteins), Hot tub lung (Mycobacterium avium)
Drug-induced ILD
Toxic or immune-mediated pulmonary drug reactions
AmiodaronePhospholipidosis; ground-glass ± consolidation
MethotrexateHypersensitivity pneumonitis pattern
BleomycinOxidative lung injury; fibrosis
Checkpoint inhibitorsImmunotherapy-related pneumonitis (irAEs)
NitrofurantoinAcute or chronic HP-like pattern
Radiation pneumonitisPost-radiotherapy; confined to radiation field
Granulomatous ILD
Non-caseating or caseating granuloma formation
SarcoidosisNon-caseating granulomas; bilateral hilar lymphadenopathy; BHL ± parenchymal
Chronic HPGranulomatous inflammation from inhaled antigens (overlaps with HP category)
Pulmonary TBCaseating granulomas; Mycobacterium tuberculosis
BerylliosisChronic beryllium disease; sarcoidosis-like
Occupational / Environmental ILD
Inhalation of inorganic or organic dusts
SilicosisCrystalline silica; mining, sandblasting; upper lobe nodules
AsbestosisAsbestos fibres; basal fibrosis; pleural plaques; mesothelioma risk
Coal worker's pneumoconiosisCoal dust; progressive massive fibrosis
Hard metal lung diseaseCobalt, tungsten carbide; giant cell interstitial pneumonia
Smoking-related ILD
Distinct from RB-ILD / DIP (listed under IIPs)
RB-ILDRespiratory Bronchiolitis-ILD
DIPDesquamative Interstitial Pneumonia
PLCHPulmonary Langerhans Cell Histiocytosis — cysts + nodules; upper lobe
Acute eosinophilic pneumoniaNew smoker; rapidly progressive; BAL eosinophilia >25%
Combined pulmonary fibrosis + emphysema (CPFE)Upper lobe emphysema + lower lobe fibrosis; severe pulmonary HTN
Rare / Other ILDs
Lymphangitic, cystic, and miscellaneous ILDs
LAMLymphangioleiomyomatosis — women of childbearing age; cystic; TSC gene
PAPPulmonary Alveolar Proteinosis — crazy paving on CT; anti-GM-CSF Ab
Eosinophilic pneumoniasSimple (Löffler), AEP, CEP, EGPA — BAL eosinophilia
Lymphangitic carcinomatosisTumour spread via lymphatics; septal thickening; known primary cancer
AmyloidosisAL amyloid deposition in lung parenchyma
ABPAAllergic Bronchopulmonary Aspergillosis — central bronchiectasis
ATS/ERS Classification Note: ILDs are grouped by aetiology and pathological pattern. IPF is the most common and most lethal ILD — always the priority diagnosis to exclude. HRCT is the cornerstone of ILD classification; surgical lung biopsy reserved for unclassifiable cases after MDT review. The UIP pattern on HRCT is diagnostic of IPF when clinical criteria are met and alternative diagnoses excluded.

Investigations

  • High-Resolution CT (HRCT) Chest — Key Imaging Test

    May show:

    • Ground-glass opacities
    • Reticulation
    • Traction bronchiectasis
    • Honeycombing

    The pattern and distribution help identify the specific type of ILD.

    Pulmonary Function Tests

    Typically show:

    • Restrictive pattern
    • Reduced total lung capacity
    • Reduced diffusion capacity (DLCO)

    Oxygen Assessment

    • Pulse oximetry
    • Exercise oxygen assessment
    • Arterial blood gas in severe disease

    Blood Tests

    Depending on the suspected cause:

    • CBC
    • Inflammatory markers
    • Autoimmune serology

    Additional Tests

    When needed:

    • Bronchoscopy with bronchoalveolar lavage
    • Lung biopsy
    • Multidisciplinary review

Diagnosis

Interstitial Lung Disease (ILD) · Diagnostic Criteria

ILD = A HETEROGENEOUS GROUP OF PARENCHYMAL LUNG DISORDERS — DIAGNOSIS REQUIRES INTEGRATION Over 200 distinct ILDs exist, sharing features of alveolar and interstitial inflammation/fibrosis. Diagnosis requires MDT integration of clinical history, HRCT pattern, PFTs, serology, and often surgical lung biopsy. Identifying the specific ILD subtype is critical as prognosis and treatment differ substantially.
Stepwise Diagnostic Approach
1
History & Exposure
Duration/onset of dyspnoea, dry cough, occupation (asbestos, silica, birds), drugs, smoking, family history, connective tissue disease symptoms.
Clinical
2
HRCT Chest
Most important diagnostic test. Identify pattern: UIP, NSIP, DIP, RB-ILD, COP, LIP, sarcoidosis, HP. Pattern guides diagnosis and may preclude biopsy.
Cornerstone
3
Pulmonary Function Tests
Typically restrictive pattern (reduced TLC, FVC, DLCO). DLCO disproportionately low in ILD with vascular involvement. Serial PFTs track progression.
Severity & monitoring
4
Serology & Labs
ANA, anti-dsDNA, RF, anti-CCP, myositis panel (Jo-1, MDA5), anti-Scl-70, ANCA, precipitins (HP), ACE (sarcoidosis), serum biomarkers (KL-6, SP-D).
Aetiology
5
Bronchoscopy / Biopsy
BAL for cell count/infection. Transbronchial biopsy for sarcoidosis/HP. Surgical lung biopsy (VATS) for definitive histology when HRCT pattern is indeterminate.
When needed
ILD Category Key Examples Typical HRCT Pattern
Idiopathic Interstitial Pneumonias (IIPs) IPF NSIP COP DIP, RB-ILD, AIP, LIP UIP (honeycombing + traction bronchiectasis, basal/subpleural) for IPF; ground-glass + subpleural sparing for NSIP; consolidation + ground-glass for COP
Connective Tissue Disease-ILD RA-ILD, SSc-ILD, myositis-ILD (anti-MDA5/Jo-1), SLE-ILD, Sjogren's-ILD NSIP pattern most common; UIP in RA; organising pneumonia in myositis; specific patterns vary by CTD
Hypersensitivity Pneumonitis (HP) Farmer's lung (thermophilic actinomycetes), Bird fancier's lung (avian proteins), hot tub lung, chemical exposures Acute/subacute: ground-glass + mosaic attenuation + air trapping. Chronic: fibrotic HP with UIP-like features; head-cheese sign
Granulomatous ILD Sarcoidosis, hypersensitivity pneumonitis, berylliosis Sarcoidosis: perilymphatic nodules, upper/mid lobe, bilateral hilar lymphadenopathy
Drug-Induced ILD Amiodarone, methotrexate, nitrofurantoin, bleomycin, checkpoint inhibitors, biologics Variable — organising pneumonia, NSIP, or diffuse alveolar damage depending on drug and mechanism
Occupational / Environmental ILD Asbestosis, silicosis, coal worker's pneumoconiosis, berylliosis Asbestosis: UIP-like, bilateral pleural plaques; silicosis: upper lobe nodules, eggshell calcification of nodes
Other / Rare ILDs LAM (lymphangioleiomyomatosis), pulmonary Langerhans cell histiocytosis, eosinophilic pneumonia, PAP (alveolar proteinosis) LAM: diffuse thin-walled cysts in young women; PLCH: upper lobe cysts + nodules in smokers; PAP: crazy paving
HRCT Pattern Key Points
UIP (Usual Interstitial Pneumonia) — honeycombing ± traction bronchiectasis, basal/subpleural/peripheral predominance → IPF until proven otherwise
NSIP pattern — bilateral ground-glass, subpleural sparing, traction bronchiectasis without honeycombing → CTD-ILD, HP, NSIP
Organising pneumonia — consolidation ± ground-glass, peribronchovascular/subpleural, reverse halo sign → COP, drug-ILD, CTD
Ground-glass predominant — DIP (smokers), subacute HP, drug reaction, acute infection
Typical UIP on HRCT in correct clinical context — biopsy can be avoided (ATS/ERS guideline)
Red Flags & MDT Approach
All ILD should be discussed at MDT (pulmonologist, radiologist, rheumatologist, pathologist) — diagnostic accuracy is significantly higher with MDT review
Rapid progression — AIP (acute interstitial pneumonia) / acute exacerbation of IPF — high mortality; treat as acute respiratory failure
Always screen for CTD — ILD may precede overt connective tissue disease by years; serological screen mandatory in all ILD
Exclude HP before diagnosing IPF — HP can mimic UIP/IPF pattern on HRCT; thorough exposure history and precipitin panel essential
FVC <50% or DLCO <35% — early lung transplant evaluation referral
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Management

Interstitial Lung Disease (ILD) · Treatment by Type

TREATMENT IS HIGHLY ILD-SUBTYPE SPECIFIC — IDENTIFYING THE CORRECT DIAGNOSIS IS ESSENTIAL What treats one ILD may harm another — immunosuppression is beneficial in inflammatory ILDs (NSIP, COP, HP, CTD-ILD) but harmful in IPF. Antifibrotic therapy is specific to fibrotic ILDs. All ILD patients need supportive care and MDT oversight regardless of subtype.
/* Shared pillars */
Universal Treatment Pillars (All ILD)
1
Remove the Trigger
Identify and eliminate causative antigen (HP), offending drug, or occupational exposure. Fundamental first step — ongoing exposure perpetuates fibrosis.
All patients
2
Pulmonary Rehabilitation
Exercise training, breathing techniques, education. Improves dyspnoea, quality of life and exercise capacity regardless of ILD subtype.
All symptomatic patients
3
Supplemental O2 & Vaccinations
LTOT if SpO2 ≤88% at rest or ≤90% on exertion. Annual influenza, pneumococcal vaccination. Prevents infective exacerbations.
All patients
4
Transplant Evaluation
Refer early for lung transplant assessment if FVC <50% predicted, DLCO <35%, rapid decline, or O2-dependent. Don't wait for end-stage.
If progressive
ILD Type Treatment of Choice Key Notes
IPF (Idiopathic Pulmonary Fibrosis) Nintedanib or Pirfenidone Antifibrotics — not immunosuppressants. Both slow FVC decline by ~50%. Do NOT use corticosteroids (harmful — PANTHER trial). Treat gastro-oesophageal reflux (common comorbidity, worsens IPF). Early transplant referral.
NSIP (Non-Specific Interstitial Pneumonia) Prednisolone ± Mycophenolate or Azathioprine Generally steroid-responsive, especially cellular NSIP. Fibrotic NSIP responds less well. Steroid-sparing agent added for maintenance. Monitor for CTD underlying cause.
COP (Cryptogenic Organising Pneumonia) Prednisolone (0.75–1 mg/kg/day) Highly corticosteroid-responsive — dramatic improvement usually within weeks. Prolonged taper over 6–12 months to prevent relapse (common if stopped too early). Excellent prognosis.
Hypersensitivity Pneumonitis (HP) Antigen removal + Prednisolone (acute/subacute) Most important step is complete antigen avoidance — disease may resolve without drugs if done early. Corticosteroids speed resolution in acute/subacute HP. Chronic fibrotic HP: antigen avoidance + consider nintedanib (progressive fibrotic HP). Relapses occur with re-exposure.
CTD-ILD (RA, SSc, Myositis) Mycophenolate mofetil or Azathioprine ± steroids Treat underlying CTD + ILD simultaneously. SSc-ILD: mycophenolate first-line (SLS II trial); nintedanib also approved. Myositis-ILD (MDA5+): often aggressive — high-dose steroids + calcineurin inhibitor + rituximab. RA-ILD: methotrexate may worsen ILD — discontinue and switch.
Sarcoidosis (pulmonary) Prednisolone if symptomatic/progressive Stage I/II often remits spontaneously — observe first. Treat if symptomatic, progressive, or extrapulmonary involvement (cardiac, CNS, hypercalcaemia). Steroid-sparing: methotrexate, azathioprine, hydroxychloroquine. Refractory: infliximab.
Drug-Induced ILD Stop the offending drug + Prednisolone if severe Most cases improve or resolve on drug withdrawal. Corticosteroids for severe/rapidly progressive cases (e.g. checkpoint inhibitor pneumonitis — high-dose IV methylprednisolone). Some drug-ILDs are irreversible (bleomycin, nitrofurantoin fibrosis).
Asbestosis / Silicosis (Pneumoconioses) No disease-modifying therapy — supportive care only Remove from exposure immediately. Treat complications (infection, respiratory failure, cor pulmonale). Asbestosis: annual surveillance for mesothelioma/lung cancer (high risk). Silicosis: whole lung lavage for silicoproteinosis; GM-CSF for autoimmune PAP if coexistent.
DIP / RB-ILD (Smoking-Related ILD) Smoking cessation + Prednisolone if persistent DIP and RB-ILD are almost exclusively smokers. Smoking cessation is the primary and often sufficient treatment. Corticosteroids if residual disease after cessation. Good prognosis if smoking stopped early.
Acute Exacerbation of IPF / AIP High-dose IV methylprednisolone + ICU-level supportive care Acute exacerbation of IPF: in-hospital mortality >50%. High-dose steroids empirically (evidence limited). Ventilatory support; consider NIV/HFNO over invasive ventilation. Urgent transplant activation if listed. AIP (Hamman-Rich): fulminant DAMP — steroids, ICU, high mortality.
Progressive Pulmonary Fibrosis (PPF) — non-IPF Nintedanib INBUILD trial: nintedanib slows FVC decline in non-IPF fibrotic ILDs that are progressing despite optimal treatment (HP, CTD-ILD, unclassifiable ILD). A major paradigm shift — antifibrotic use now extends beyond IPF.
Monitoring on Treatment
Spirometry + DLCO — every 3–6 months; FVC decline ≥10% or DLCO ≥15% = significant progression
6-minute walk test — every 6 months; desaturation and distance are prognostic markers
HRCT — annually or if acute deterioration; compare with baseline
Drug toxicity monitoring — nintedanib (LFTs, GI); pirfenidone (LFTs, photosensitivity); steroids (glucose, BP, bone density, eye pressure); mycophenolate/azathioprine (FBC, LFTs)
Echocardiography — screen for pulmonary hypertension (common complication of advanced ILD)
Lung Transplantation
Referral criteria — FVC <50%, DLCO <35%, O2-dependent, progressive decline despite treatment, hospitalisations for respiratory failure
IPF — refer at diagnosis or early; waitlist mortality is high, don't delay
Bilateral lung transplant preferred over single lung for ILD (better outcomes)
5-year survival post-transplant — ~50–60% for ILD; best outcomes in younger, non-IPF patients
Palliative care — integrate early; symptom management, opioids for refractory dyspnoea, psychological support

Complications

  • Progressive pulmonary fibrosis
  • Chronic hypoxemia
  • Respiratory failure
  • Pulmonary hypertension
  • Cor pulmonale
  • Acute exacerbation
  • Increased risk of lung cancer
  • Death

Prognosis

  • Prognosis varies greatly depending on the specific Interstitial lung disease (ILD) .
  • Some inflammatory Interstitial lung disease (ILD) may improve with treatment.
  • Fibrotic Interstitial lung disease (ILD) are often progressive.
  • Prognosis is worse with:
    • Extensive fibrosis
    • Declining lung function
    • Severe hypoxemia
    • Pulmonary hypertension
    • Acute exacerbations
  • Early diagnosis and treatment of reversible causes may improve outcomes.

Key Points / Clinical Pearls

  • Interstitial lung disease (ILD) is a group of diseases, not a single disease.
  • Progressive dyspnea and dry cough are classic symptoms.
  • Fine inspiratory crackles are a common examination finding.
  • HRCT is the key imaging test for Interstitial lung disease (ILD).
  • Pulmonary function tests usually show a restrictive pattern with reduced DLCO.
  • Always ask about occupational, environmental, medication, and autoimmune causes.
  • Honeycombing suggests established pulmonary fibrosis.
  • Treatment depends on the specific Interstitial lung disease (ILD) subtype.