Interstitial lung disease (ILD)


Introduction

Interstitial lung disease (ILD), sometimes called diffused parenchymal diseases is a group of diseases characterized by a combination of chronic inflammation within the lung, consisting of an accumulation of chronic inflammatory cells (predominantly lymphocytes and macrophages) and increased levels of numerous pro-inflammatory cytokines, chemokines, and cell surface molecules; and varying degrees of lung fibrosis.


Classification

Major ILDs of known aetiology (35% overall):

  • Pneumoconioses (e.g. asbestosis, silicosis)
  • Extrinsic allergic alveolitis (hypersensitivity pneumonitis)
  • Iatrogenic ILD caused by drugs and/or radiation
  • Post-infectious ILD

Major ILDs of unknown aetiology (65% overall):

  • Sarcoidosis
  • Idiopathic interstitial pneumonias (IIP):
    • IPF with a histopathological pattern of usual interstitial pneumonia (UIP) (55% of IIPs)
    • Nonspecific interstitial pneumonia (NSIP) (~25% of IIPs)
    • Respiratory bronchiolitis ILD, occurring in smokers (~10% of IIPs)
    • Desquamative interstitial pneumonia (~5% of IIPs)
    • Cryptogenic organising pneumonia (~3% of IIPs)
    • Lymphoid interstitial pneumonia (LIP) (~1% of IIPs)
    • Acute interstitial pneumonia (AIP) (~1% of IIPs)
  • ILD in CTDs and in collagen-vascular diseases:
    • ILD in rheumatoid arthritis
    • ILD in progressive systemic sclerosis

Aetiology

Schematic classification of interstitial lung diseases according to aetiology. The finding of histological usual interstitial pneumonitis in a patient with an idiopathic interstitial pneumonia leads to the specific diagnosis of idiopathic pulmonary fibrosis. | NSIP = non-specific interstitial pneumonitis. | Mikolasch, T. A., Garthwaite, H. S., & Porter, J. C. (2017). Update in diagnosis and management of interstitial lung disease . Clinical medicine (London, England), 17(2), 146–153. https://doi.org/10.7861/clinmedicine.17-2-146

Upper lobe predominance:

BREASTS
  • Berylliosis (& other pneumoconiosis)
  • Radiation fibrosis
  • Eosinophilic (hypersensitivity) pneumonia
  • Allergic bronchopulmonary pneumonia
  • Ankylosing spondylitis (only rheumatic disease affecting upper lobes)
  • Sarcoidosis (mediastinal involvement)
  • Tuberculosis
  • Silicosis

Lower lobe predominance:

AIDS
  • Asbestosis
  • Idiopathic pulmonary fibrosis
  • Drug-induced fibrosis: Amiodarone, nitrofurantoin, methotrexate
  • Scleroderma (& other connective tissue disease)

Clinical features

  • Progressive dyspnoea
  • Non-productive cough
  • Associated features (depending on etiology)
  • Features of right heart failure (severe disease):
    • ↑ JVP
    • Peripheral oedema
    • Loud P2
    • S3

Diagnosis

Suggested approach to the diagnosis of ILD. | Abbreviations: BAL = bronchoalveolar lavage fluid; HRCT-high-resolution computed tomography; ILD = interstitial lung disease; VATS = video-assisted thorascopic surgery. | Meyer K. C. (2014). Diagnosis and management of interstitial lung disease. Translational respiratory medicine, 2, 4. https://doi.org/10.1186/2213-0802-2-4

HRCT:

Diagnostic criteria for a definite usual interstitial pneumonitis pattern on high resolution computerised tomography: 1 – subpleural, basal predominance (red arrows); 2 – reticular abnormality (blue arrow); 3 – honeycombing with or without traction bronchiectasis (yellow arrow); 4 – absence of features inconsistent with usual interstitial pneumonitis pattern. | BAL = bronchoalveolar lavage; GOR = gastro-oesophageal reflux; HRCT = high-resolution computerised tomography; ILD = interstitial lung disease; IPF = idiopathic pulmonary fibrosis; MDT = multidisciplinary team; PFT = pulmonary function test; PHT = pulmonary hypertension | Mikolasch, T. A., Garthwaite, H. S., & Porter, J. C. (2017). Update in diagnosis and management of interstitial lung disease . Clinical medicine (London, England), 17(2), 146–153. https://doi.org/10.7861/clinmedicine.17-2-146

Differential diagnosis:

  • Pulmonary oedema
  • ARDS
  • Bacterial/fungal/viral pneumonia

Management

Schematic interstitial lung disease treatment algorithm. *No robust evidence for managing exacerbations with variation between centres, should be discussed with specialist centre if possible. | BAL = bronchoalveolar lavage; GOR = gastro-oesophageal reflux; HRCT = high-resolution computerised tomography; ILD = interstitial lung disease; IPF = idiopathic pulmonary fibrosis; MDT = multidisciplinary team; PFT = pulmonary function test; PHT = pulmonary hypertension | Mikolasch, T. A., Garthwaite, H. S., & Porter, J. C. (2017). Update in diagnosis and management of interstitial lung disease . Clinical medicine (London, England), 17(2), 146–153. https://doi.org/10.7861/clinmedicine.17-2-146

Supportive management:

For those interstitial lung disorders with known causes, avoidance of irritant is essential.
  • Smoking cessation
  • Pulmonary rehabilitation (help improve functionality)
  • Good pulmonary hygiene
  • Supplemental oxygen (for hypoxemia: SaO2 < 88)

Corticosteroids:

Progressive disease despite the elimination of offending agent. Corticosteroids intercept the inflammatory process within the lungs.

Immunosuppressant therapy:

For cases that do not respond to corticosteroids

Lung transplant


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