Interstitial lung disease

Interstitial lung disease (ILD), also called diffuse parenchymal lung disease, is a group of disorders characterised by fibrosis of the lungs. There are many different types. The name implies that these disorders only affect the interstitium of the lung and not the parenchyma (the airways and alveoli), but many of these disorders affect the parenchyma as well.

It's more common in males, but ILD is rare overall.

Etiology

The list of causes of ILD is basically endless, but here are some of the most typical:

Idiopathic
- Idiopathic pulmonary fibrosis
- Idiopathic interstitial pneumonia

Environmental and occupational exposure
- Silica crystals (causes "silicosis")
- Asbestos (causes "asbestosis")
- Coal dust (causes "coal worker pneumoconiosis")
- Mineral dust
- Organic dust
Drugs
- 350+ drugs can cause ILD
Auto-immune and rheumatological diseases
Infiltrative disorders
- Sarcoidosis
- Amyloidosis

Most cases of ILD are idiopathic. The most common identifiable causes include exposure- and drug-induced ILD.

Clinical features

Interstitial lung disease causes gradual onset dyspnoea and sometimes cough.

Many ILDs are complicated by pulmonary hypertension, which may be symptomatic.

Diagnosis and evaluation

Pulmonary function testing is obligatory.

ILD has characteristic imaging findings. Radiography usually shows a reticular pattern, a nodular pattern, or a mix of the two. However, high-resolution CT is obligatory in the evaluation. Some types of ILD have characteristic CT findings, but most types show any combination of the following patterns:

Ground glass opacities
Lung consolidation
Reticular opacities
Nodules

Idiopathic pulmonary fibrosis has a characteristic sign called honeycombing, named after the honeycomb-like appearance the lung takes on due to formation of clustered cystic air spaces.

Silicosis causes "eggshell calcification", which is well-defined sickle-shaped calcification of the rims of the hilar lymph nodes. Bilateral diffuse ground glass opacities and uniformly distributed small nodules are also typical.

Bronchoalveolar lavage and lung biopsy may be indicated if the type remains uncertain.

COPD

Chronic obstructive pulmonary disease (COPD) is characterised by persistent respiratory symptoms and airflow limitation due to airway and/or alveolar abnormalities. It’s common, preventable, and treatable. It is defined as a post-bronchodilator FEV1/FVC ratio of < 0,70.

It affects 11,7% of the world and it’s the third leading cause of death worldwide. Prevalence is expected to rise, and it’s expected to be the leading cause of death in 15 years.

COPD has two phenotypes, chronic bronchitis and emphysema.

Imaging

Imaging is not necessary for the diagnosis of COPD. In case of emphysema, chest radiography will show hyperinflation of the lungs, as evidenced by horizontal ribs, widened intercostal space, increased anterioposterior diameter (seen on the lateral view), flattened diaphragm, and increased transparency of the lung.