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Introduction
Interstitial lung diseases (ILDs) affect the lung interstitium, i.e. the space between the alveolar epithelium and the capillary endothelium, causing inflammation and fibrosis.
The two main types of interstitial lung disease are pulmonary fibrosis and sarcoidosis. Other types include occupational lung diseases (pneumoconiosis), and interstitial lung disease secondary to connective tissue diseases.
  • Sarcoidosis tends to occur in younger adults, and can also affect any other organ system in the body, although in 90% of cases the lungs are involved
  • Sarcoidosis has a more benign prognosis and in many cases, resolves by itself
  • Pulmonary fibrosis tends to occur in older adults, and causes significant morbidity and mortality

Many patients are treated with steroids, although the evidence for their benefit is not strong, and, depending on the cause – many patients (mainly those with idiopathic pulmonary fibrosis) do not respond to treatment

Epidemiology and Aetiology

  • Incidence of all ILDs combined is about 30 per 100 000
  • Types of interstitial lung disease
    • Idiopathic pulmonary fibrosis
      • Poor prognosis – median survival 3-5 years. Typically older adults
    • Sarcoidosis
      • Usually good prognosis. Can affect younger adults
    • Pneumoconiosis
      • Variable prognosis depending on the cause
    • Drug induced ILD
      • Amiodarone, methotrexate
    • Hypersensitivity ILD
      • Usually has a good prognosis if the allergen is avoided

Typical presentation

  • Often slowly progressive
    • Occasionally may mimic an acute pneumonia
  • Dry cough
  • Progressive shortness of breath
  • May have clubbing
  • May have diffuse inspiratory crackles
  • Wheeze, haemoptysis and chest pain are rare
  • Investigations
    • Restrictive respiratory pattern of spirometry
    • Abnormal CXR

What is Interstitial lung disease?

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.

Sarcoidosis

SARCOIDOSIS is covered in a separate article

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)
It typically present in older patients, with a peak age of onset in patients aged 50-60.
Pulmonary fibrosis has a very poor prognosis – the median age of survival is only 3-4 years.

Investigations

  • Blood
    • FBC (raised ESR), Rh factor (+ve 50% patients), ANA (30% +ve)
  • CXR
    • Irregular, reticulo-nodular shadows, often in lower zones, sometimes called the reticulonodular pattern
    • CXR is often normal
  • CT
    • Usually a “high resolution CT” (HRCT)
    • Ground-glass opacification
    • “Honeycombing”
    • “Mosaicism”
  • Lung Function Tests (spirometry)
    • Restrictive Pattern
  • ABG
    • Hypoxaemia
  • Transbronchial or open lung biopsy to confirm histological diagnosis
    • Assists in defining the type of ILD that is present

Management

The exact management plan is very individualised for the patient. Some, all or none of the below measures may be used. For idiopathic pulmonary fibrosis, no treatment has been proven to prolong survival.

Pulmonary rehabilitation
  • Early referral to a specialist centre for pulmonary rehabilitation is important

Smoking cessation

Corticosteroids

  • 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.
  • Evidence is lacking
  • Treatment is often combined with azathioprine

Immunosuppression

  • Combined immunosuppressive therapy can also be used including azathioprine and cyclophosphamide in conjunction with steroids.

Treat associated disorders

Lung transplant

  • Should be considered in suitable candidates
Most patients with Idiopathic pulmonary fibrosis die within 5 years of diagnosis. Most other types of ILD have a better prognosis.
  • Sarcoidosis – treatment only indicated if disease is progressive and / or has significant symptoms
    • Prednisolone – 0.5mg/Kg/day is usually the recommended treatment, for one month, and then weaning to the lowest effective dose, reviewed every 6-12 months
  • Connective tissues diseases – treat the underling disorder. Often a similar prednisolone regimen to that recommended for sarcoidosis
  • Hypersensitivity pneumonitis – avoidance of the antigen is the primary treatment. Prednisolone may be used if there is severe or progressive disease

Pneumoconioses

Pneumoconiosis is covered in more detail in its own article.

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.

References

  • Interstitial lung disease - a diagnostic approach - RACGP
  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

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