Interstitial Lung Disease / Pulmonary Fibrosis

Original article by James Killeen | Last updated on 20/2/2016
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Introduction

These diseases affect the lung interstitium, i.e. the space between the alveolar epithelium and the capillary endothelium, causing inflammation and fibrosis.

 

What is Pulmonary Fibrosis?

This can be a source of confusion to many a medical student. Pulmonary fibrosis is the end result of many respiratory diseases, it is characterised by:
  • Scar tissue in the lungs.
  • Decreased compliance giving a RESTRICTIVE pattern in pulmonary function tests. (Fev1/FVC ratio >80%).
  • End stage is “honeycomb lung”, cystic spaces develop in fibrotic lungs.
 
It can be classified according to involvement:
  • Localised (e.g following unresolved pneumonia)
  • Bilateral (e.g. in TB)
  • Widespread (e.g. in idiopathic pulmonary fibrosis or pneumoconiosis)
 
The four main clinical features in fibrotic lung conditions can be remembered using the mnemonic the four D’s:
  • Dry cough
  • Dyspnoea (progressive)
  • Digital clubbing
  • Diffuse inspiratory crackles 
Although many diseases can cause pulmonary fibrosis, patients will tend to present with SOB and changes on CXR.

 

Idiopathic Pulmonary Fibrosis / Cryptogenic Fibrosing Alveolitis

This is a relatively rare, progressive, chronic pulmonary fibrosis of unknown aetiology. It typically occurs in patients 45-65 years and involves the lower lobes.
 
The main features are progressive breathlessness, dry cough, considerable weight loss and fatigue/malaise. The alveolar walls are affected predominantly in the subpleural regions of the lower lobes. There are an increased number of chronic inflammatory cells in the interstitium. This histological pattern is called “Usual Interstitial Pneumonitis” (UIP). Other patterns of the disease can include DIP (Desquamative Interstitial Pneumonitis) and Bronchiolitis Obliterans, which will be discussed later.
 
Over time this disease progresses to cause pulmonary hypertension, cor pulmonale and type 1 respiratory failure.
Signs O/E include:
  • Reduced chest expansion
  • End inspiratory crackles
  • Clubbing (2/3 patients)
 

Investigations

  • Blood:  FBC (raised ESR), Rh factor (+ve 50% patients), ANA (30% +ve).
  • CXR:       irregular, reticulo-nodular shadows, often in lower zones.
  • CT:          ground-glass opacification.
  • Lung Function Tests:       Restrictive Pattern.
  • ABG:      hypoxaemia
  • Transbronchial or open lung biopsy to confirm histological diagnosis.
 

Management

A large proportion of patients do not respond well to corticosteroid treatment. High dose prednisolone for 6 weeks followed by a tapered dose is recommended in the Oxford Clinical Handbook.
 
Combined immunosuppressive therapy can also be used including azathioprine and cyclophosphamide in conjunction with steroids.
Most patients die within 5 years of diagnosis
 

Pneumoconioses

Coal worker’s Pneumoconiosis

The incidence of this disease is related to total coal dust exposure. It results from inhalation of coal dust over 15-20 years. Two syndromes exist:
  • Simple Pneumoconiosis- Usually asymptomatic, but can have co-existent bronchitis. Diagnosis is made from CXR on finding small, round opacities in the upper zones. Avoidance of exposure to further dust can stop it from progressing. Patients are entitled to claim compensation via the Industrial Injuries Act.
  • Progressive Massive Fibrosis- Can occur on top of simple CWP. Large, round fibrotic nodules >10mm seen on CXR, usually upper zones. Nodules can become infected by tuberculosis. The associated emphysema is severe. Cough, dyspnoea and production of black sputum may be present (sputum black due to ruptured, cavitating lesions, hence the name “the black lung”). This can progress despite cessation of exposure to dust, there is no specific treatment. Patients will eventually develop pulmonary hypertension and cor pulmonale.
Caplan’s Syndrome – Is the association between CWP and Rheumatoid Arthritis.
 

Asbestosis

A diffuse pulmonary fibrosis caused by inhalation of asbestos. In the UK, exposure to asbestos is most likely to occur during building work or renovations, as in the past asbestos was used in housing materials. Occupations such as roofers, builders, plumbers and pipe laggers are at higher risk. There have been reported incidences in the past of these workers’ partners being affected from continued exposure through garments. Blue asbestos (crocidolite fibres) is the most dangerous and white asbestos (chrystolite fibres) the least. A considerable lag of 20-40 years exists between exposure and presentation. Clinical features are that of fibrosis, dyspnoea, dry cough, clubbing and end inspiratory crackles. Prognosis is poor.
 
It is important to note here that there is a strong correlation between exposure to asbestos and the development of mesothelioma.
 

Extrinsic Allergic Alveolitis

This is also known as hypersensitivity pneumonitis and is a widespread inflammatory reaction. It results from repeated exposure to antigens to which the individual has already been sensitised. Examples of these antigens include:
  • Mouldy hay (Farmer’s lung)
  • Bird Faeces (bird fancier/pigeon fancier’s lung)
  • Cotton fibres (bysinossis)
  • Sugar cane fibres (bagassosis) 
 
Lymphocytes and macrophages infiltrate the small airways after antigen exposure. This either resolves or leads to pulmonary fibrosis. Clinical features are SOB, cough, fever which occur hours after antigen exposure. Chronically, features include: weight loss, progressive dyspnoea, type 1 resp. Failure and cor pulmonale.
Lung Function tests show a reversible restrictive pattern. CXR can show upper zone fibrosis and/or honeycomb lung.
Management is to remove the source of the allergen primarily. Acutely the patient should be given Oxygen, Hydrocortisone 200mg IV, oral prednisolone 40mg (reducing dose). Long term steroids can improve the outcome for patients with chronic symptoms.

 

Goodpasture’s Syndrome

This is a syndrome characterised by glomerulonephritis and respiratory disease together. It is driven by a type 2 hypersensitivity reaction whereby IgG anti-basement membrane antibodies attach to the glomerulus to cause glomerulonephritis but can also react with the alveolar membrane to cause pulmonary haemorrhage.
The three features to remember are:
Treatment is with corticosteroids, but in some cases plasmapheresis to remove autoantibodies has shown great success.
 

Idiopathic Pulmonary Haemosiderosis

A rare condition typically occurring in children under seven years of age. It causes cough, haemoptysis and dyspnoea. Treatment is with corticosteroids and azathioprine. Prognosis is poor.