Interstitial Lung Diseases

Question 1

Diffuse Parenchymal Lung Disease (DPLD)

Answer 1

Diffuse Parenchymal Lung Disease (DPLD) are a large group of conditions characterised by inflammation centred on the interstitium of alveolar walls

Question 2

The lung interstitium

Answer 2

The lung interstitium is the tissue lying between alveoli and containing pulmonary artery capillaries. Normally the interstitium is a thin layer, allowing the alveoli and capillaries to lie very close to one another enabling optimal diffusion.

Question 3

Pathophysiology of diffuse parenchymal lung disease?

Answer 3

In DPLD, the interstitium becomes expanded by an inflammatory cell infiltrate (“pneumonitis” or “alveolitis”) which impairs gas exchange and causes breathlessness.

Episodes of alveolitis (pneumonitis) may be followed by complete regeneration without residual damage to alveoli

However, in some instances, the inflammation is followed by repair with scarring: Macrophages release fibrogenic cytokines and stimulate fibroblasts in the interstitium to secrete collagen (scar tissue). The thickened alveolar walls are ineffective at gas exchange, resulting in worsening breathlessness.

Question 4

Pneumonitis

Answer 4

inflammation of the lung parenchyma i.e. the alveoli - alveolitis is an alternative name for pneumonitis. NON INFECTIVE cause.

Question 5

Pneumonia

Answer 5

Inflammation of the lung parenchyma due to an infective agents

Question 6

Causes of DLPDs

Answer 6

There are a huge number (over 200) of DPLD can be caused by anything which sets up chronic inflammation within the interstitial space of alveolar walls.
The numerous causes can be divided into 5 basic categories:

• unknown cause (idiopathic interstitial lung diseases). The most common is idiopathic pulmonary fibrosis (previously known as cryptogenic fibrosing alveolitis).
• pneumoconioses (inhaled inorganic/mineral dusts)
  * coal dust (coal workers’ pneumoconiosis), silica (silicosis), asbestosis (asbestosis).
• extrinsic allergic alveoli8s (inhaled organic particles; called hypersensitivity pneumonitis in USA) eg. Bird Fancier lung, Farmer lung.
• side effects of treatment
• therapeutic chest radiation.
• certain drugs eg. bleomycin, amiodarone.
• multisystem diseases involving the lung
• eg. sarcoid, connective tissue diseases (SLE, rheumatoid arthritis, scleroderma, Sjögren’s, polymyositis, dermatomyositis).

Question 7

Diagnosing ILD

Answer 7

• History and examination. In particular, a meticulous history (including occupational and environmental exposure in detail) is important in attempting to identify an underlying cause.
Investigations:
• Chest radiograph may show reticulation.
• Spirometry will show a restrictive defect.
• High resolution CT scan (very thin (1-2mm) sections through the lungs) shows reticulation and may help elucidate the underlying cause.
• Lung biopsy for histological examination is sometimes necessary to achieve a diagnosis but is not a first line investigation.

Question 8

Long term complications ILD

Answer 8

DLPDs (ie. pulmonary fibrosis) are an important cause of cor pulmonale (right heart failure due to lung disease).
The fibrosis of the lung tissue causes obliteration of pulmonary arterioles and capillaries, resulting in gradual development of pulmonary hypertension.
The right ventricle undergoes compensatory right ventricular hypertrophy. Eventually, the right ventricle decompensates and right heart failure ensues.