Idiopathic Interstitial Lung Disease

Background

• Interstitial lung disease encompasses a range of conditions which cause damage to the interstitial lung tissue, resulting in an impairment of gas transfer across the alveolar membrane
• Other causes of interstitial disease include sarcoidosis; connective tissue disorders/vasculitides; drugs
• In general, they can be classified as
  • Acute
    • Acute interstitial pneumonia (diffuse alveolar damage)
      • This is a rare condition, indistinguishable from ARDS, of unknown cause
  • Subacute
    • Cryptogenic Organising Pneumonia (organising pneumonia)
      • Also known as bronchiolitis obliterans organising pneumonia (BOOP)
    • Non-specific interstitial pneumonia
      • Really just used when a case does not fit into any one of the other ILD classifications and is therefore without a diagnosis (of which there is a good cohort- thus almost making it a diagnosis in its own right)
  • Chronic
    • Lymphoid Interstitial pneumonia (LIP)
    • Desquamative interstitial pneumonia (DIP)
    • Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD)
    • Idiopathic pulmonary fibrosis (usual interstitial pneumonia)

Idiopathic Pulmonary Fibrosis

Background

• Progressive fibrosing interstitial pneumonia of unknown cause
  • Histology is suggestive of a chronic inflammatory pattern
    • ?autoimmune; ?viral triggers (e.g. EBV); ?occupational exposures (e.g. dusts/metals etc); ?drugs (e.g. antidepressants); ?chronic GORD reflux aspiration
    • Smoking is a risk factor
  • Genetic factors are probably important
• Usually presents in middle age – older (>55 years old) patients

Clinical Presentation

• Insidious onset
  • Dry/non-productive cough
  • Worsening shortness of breath, particularly worse on exertion
  • (Obstructive sleep apneoa)
• Other features include
  • finger clubbing
  • fine late inspiratory crackles
  • cyanosis
  • rarely, other constitutional symptoms e.g. flu-like illness, fatigue, weight loss; myalgia

Investigations

• CXR
  • Reticular shadowing (normal bronchi but opaque interstitium)
• CT
  • Ground glass (better prognosis) and/or Honeycombing
• Laboratory tests
  • FBC
    • Mild anaemia (may be normal)
  • Polyclonal hyperglobulinaemia
  • PV/CRP can be raised
  • ABGs as necessary
• Lung function tests
  • Can show a restrictive pattern (reduced lung volume and FEV1 but ratio normal) with reduced gas transfer
• Rarely, bronchialveolar lavage (lymphocyte count)
  • High BAL lymphocyte count is associated with a better response to treatment

Management

• Unfortunately, mainly supportive, although acetylcysteine, azathioprine and prednisolone can be tried
• 5 year survival is only 50-60%

NB As IPF/UIP is a diagnosis of exclusion- it is crucial to rule out other causes of pulmonary fibrosis (Mnemonic – BREAST CA) e.g.

• Bleomycin (or other cytotoxic drugs e.g. methotrexate)
• Radiation
• Extrinsic allergic alveolitis or other occupational disease e.g. pneumoconiosis
• Ankylosing Spondylitis
• Sarcoidosis
• Tuberculosis
• Crytogenic (I.e. idiopathic disease)
• Asbestosis/Azathioprine