- Clinical science
Interstitial 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.
Idiopathic pulmonary fibrosis (IPF): most common
- Risk factors: cigarette smoking, environmental or occupational exposures, chronic aspiration, genetic predisposition
Other idiopathic subtypes
- Desquamative interstitial pneumonia (DIP)
- Nonspecific interstitial pneumonia (NSIP)
- Cryptogenic organizing pneumonia (COP)
- Respiratory bronchiolitis-associated interstitial lung disease (RB-ILD)
- Acute interstitial pneumonia (AIP)
- Lymphoid interstitial pneumonia (LIP)
- Idiopathic pleuroparenchymal fibroelastosis
Occupational, environmental, and iatrogenic causes
- (e.g., , )
- Radiation pneumonitis
Secondary to underlying disease
- Granulomatous ILD:
- Infectious diseases (eg, tuberculosis, legionellosis)
- Alveolar filling disease
- Hypersensitivity reactions
- Connective tissue disorders
- Bronchoalveolar carcinoma
- Main symptoms
- Later stages of disease: digital clubbing due to chronic hypoxia
- IPF: The majority of patients (> 70%) do not respond to therapy and experience progressive respiratory failure.
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
- Normal in approximately 10% of patients.
- Increase in reticular opacities (sign of fibrosis)
- Ground-glass opacities and honeycombing
- CT or HR-CT: Irregular thickening of the interlobular septa, honeycombing, and bronchiectasis
- Bronchoalveolar lavage
- 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.
- Arterial blood samples show: elevated alveolar-arterial partial pressure of oxygen gradient, decreased partial pressure of oxygen
- Screen for rheumatic and autoimmune diseases.
- 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
- Oxygen for symptomatic or end-stage ILD
- Lung transplantation in end-stage ILD