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
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