Interstitial Lung Disease

Question 1

What happens in diffuse parenchymal lung diseases (=intersitital lung diseases)?

Answer 1

• large group of conditions characterised by inflammation centres on the interstitium of alveolar walls
• interstitium becomes expanded by inflammatory cell infiltrate (‘pneumonitis’ or ‘alveolitis’)
• impairs gas exchange + causes breathlessness
• episodes of alveolitis may be followed by complete regeneration without residual damage to alveoli

Question 2

With interstitial lung disease where most inflammation may completely regenerate, sometime the inflammation is followed by repair with scarring.

What happens here?

Answer 2

• macrophages release fibrogenic cytokines
• stimulate fibroblasts in interstitium
• secrete collagen (scar tissue)
• thickened alveolar walls are ineffective at gas exchange
• resulting in worsening breathlessnes

Question 4

What is meant by the terms ‘pneumonitis’, ‘alveolitis’ and ‘pneumonia’?

Answer 4

• pneumonitis - inflammation of lung parenchyma ie. the alveoli (alveolitis is an alternative name) - usually due to non-infective causes. Inflammation is limited to interstitium.
• pneumonia - inflammation of the lung parenchyma due to an infective agent - characterised by consolidation - acute inflammatory exudate filling alveolar spaces.

Question 5

There are 200+ DPLDs. They can be caused by anything which sets up chronic inflammation within the interstitial space of alveolar walls.

What are the 5 basic categories that can divide up the causes?

Answer 5

• unknown cause (idiopathic intersitital lung disease)
• pneumoconioses (inhaled inorganic/mineral dusts), eg. coal dust, silica, asbestos
• extrinsic allergic alveolitis (inhaled organic) eg. bird fancier lung, farmer’s lung
• side-effects of treatment - eg. therapeutic chest radiation, certain drugs (amiodarone)
• multisystem diseases involving lung eg. sarcoid, SLE, RA, scleroderma

Question 6

How is interstitial lung disease diagnosed?

Answer 6

• history + exam
  
  • a meticulous history vital in identifying cause
• CXR -> reticulation
• spriometry -> restrictive
• high-res CT -> reticulation
• lung biopsy sometimes necessary

Question 7

What are signs and symptoms of interstitial lung disease?

Answer 7

• dry cough, progressive dyspnoea, wheeze, chest pain
• clubbing
• reduced chest wall expansion bilaterally
• dull percussion note
• inc vocal resonance
• bronchial breathing
• fine, late-pan inspiratory crackles

Also depends on the underlying cause

Question 8

How do DLPDs such as pulmonary fibrosis cause cor pulmonale (right heart failure due to lung disease)?

Answer 8

• important cause of cor pulmonale
• fibrosis of lung tissue obliterates pulm arterioles + caps
• -> gradual development of pulmonary hypertension
• right ventricule undergoes compensatory right ventricular hypertrophy
• eventually, right ventricle decompensates
• right heart failure ensues

Question 9

What is the management of intersitital lung disease?

Answer 9

• oxygen
• pulmonary rehabilitation
• corticosteroids, cycophosphamide, azothiaprine
• lung transplantation