Interstitial lung diseases (ILDs) are a heterogeneous group of disorders marked by inflammatory changes in the alveoli. ILDs may be idiopathic or due to secondary causes such as autoimmune disease, pharmacotherapeutic changes, or exposure to toxic substances. These changes can cause irreversible fibrosis and impaired pulmonary function. The main symptoms are exertional dyspnea and a dry cough. Bibasilar inspiratory crackles or rales are usually heard on auscultation. Treatment is based on the underlying cause. Immune modulators and corticosteroids are used in cases of unknown etiology. In advanced stages of disease ILD can result in pulmonary insufficiency and respiratory heart failure with right ventricular insufficiency.
Occupational, environmental, and iatrogenic causes
- (e.g., , )
- Radiation pneumonitis
- Chemotherapeutic agents
- Other agents
Secondary to underlying disease
- Granulomatous ILD
- Hypersensitivity reactions
- Connective tissue disorders
- Infectious diseases
- Alveolar filling diseases
- Bronchoalveolar carcinoma
- Idiopathic pulmonary fibrosis (IPF)
Other idiopathic subtypes
- Acute interstitial pneumonia (AIP): an idiopathic, interstitial lung disease with an acute onset that can progress rapidly to respiratory failure
- Cryptogenic organizing pneumonia (COP): a rare, noninfectious type of pneumonia that is characterized by inflammation of the bronchioles and the surrounding structures
- Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD)
- Desquamative interstitial pneumonia (DIP)
- Nonspecific interstitial pneumonia (NSIP)
- Lymphoid interstitial pneumonia (LIP)
- Idiopathic pleuroparenchymal fibroelastosis
- Main symptoms
- Later stages of disease
Due to the wide variety of subtypes and symptoms, there is no generally recommended diagnostic algorithm. Physical examination, serology, pulmonary function tests, and imaging (chest X-ray, CT scan) is performed almost always, while lavage or biopsy depend on the individual case.
- Pulmonary function tests
- Laboratory tests
- Normal in approx. 10% of patients
- Increase in reticular opacities (sign of fibrosis)
- Ground-glass opacities
- CT or HR-CT
- Indications: atypical or rapidly progressive symptoms
- In patients with minimal signs or symptoms and stable disease, close observation (e.g., PFTs, HR-CTs over several months) may be sufficient.
- Bronchoalveolar lavage 
- In secondary disease, the first step is to limit exposure to the toxic substance, cease therapy with the drug causing symptoms, or treat the underlying disease.
- Antibiotics if bacterial is suspected
- Corticosteroids and immune modulators
- Pirfenidone and nintedanib are commonly used for ILD.
- Oxygen for symptomatic or end-stage ILD
- Lung transplantation in end-stage ILD
- The majority of patients with IPF (> 70%) do not respond to therapy and experience progressive respiratory failure.