Interstitial Lung Processes and Their Fibrotic Progression
Interstitial lung processes (ILPs) include more than 200 clinical units that share diffuse involvement of lung tissue and thus have similar clinical, radiological, and functional findings. However, their broad differential diagnosis is particularly problematic.
ILPs and Their Clinical Presentation
Interstitial lung processes are a heterogeneous group of lung conditions characterized by acute and chronic inflammatory processes, usually accompanied by irreversible fibrosis of the interstitial and alveoli. Clinically, most ILPs manifest as progressive exertional and later resting dyspnea, fatigue, cough, and in advanced stages, hypoxemia-induced cyanosis. Some units may also exhibit clubbing of the fingers or the presence of crackles heard over the lung bases.
Care for Patients with ILPs and Their Prognosis
Care for patients with ILPs primarily involves pulmonologists, sometimes rheumatologists. Differential diagnosis can be challenging, relying on clinical, radiological, and histopathological findings. Accurate and timely diagnosis is crucial for starting optimal therapy. Histological findings can help predict the response of ILPs to treatment.
Processes characterized mainly by inflammation may achieve full regression spontaneously or with treatment. In contrast, processes with extensive fibrosis can usually only be stabilized or the progression slowed by treatment. The progression is responsible for the gradual worsening of lung functions, respiratory difficulties, quality of life, and an increased risk of premature death.
Diagnostics
Differential diagnosis typically begins with history taking and a physical examination. Laboratory findings in ILPs are not pathognomonic and often do not significantly aid in diagnosis. Pulmonary function tests reveal a restrictive ventilatory defect and a significant decrease in lung compliance. The diffusion capacity across the alveolar-capillary membrane, expressed by the transfer factor (TLCO), is significantly reduced.
The foundation of imaging methods is the anteroposterior chest X-ray. HRCT (high-resolution computed tomography) provides more detailed information about interstitial involvement. Bronchoscopy with bronchoalveolar lavage is a less commonly used diagnostic method. Pulmonary biopsy is an integral part of the diagnostic process for patients with ILPs.
Progressive Fibrosing ILPs Other Than IPF
One subgroup of ILPs is idiopathic interstitial pneumonias. The most serious and common unit (up to 50% of all ILPs) is idiopathic pulmonary fibrosis (IPF). Non-specific interstitial pneumonia (NSIP) or unclassifiable idiopathic interstitial pneumonia (UIP) can develop similar phenotypes. The 5-year survival rate from the diagnosis of NSIP is around 50%, whereas for IPF, the median survival is less than 5 years. Unclassifiable ILPs have somewhat better but still high mortality (up to 30% within 5 years).
The lungs can also be affected by systemic connective tissue diseases. ILPs develop in about 15% of patients with these diagnoses and are a significant cause of mortality in many cases. The highest incidence of pulmonary fibrosis occurs in systemic sclerosis but can also develop in patients with rheumatoid arthritis, polymyositis, dermatomyositis, systemic lupus erythematosus, and Sjögren's syndrome.
The chronic form of another unit – exogenous allergic alveolitis (hypersensitivity pneumonitis) – with a picture of pulmonary fibrosis, develops in susceptible individuals after prolonged or repeated exposure to low-concentration organic antigens (e.g., avian proteins or molds). The median survival from diagnosis is about 5 years. Long-term inhalation (> 10 years) of inorganic dust (asbestos fibers, silica dust) is associated with the development of pneumoconioses such as asbestosis and silicosis. Asbestosis reduces life expectancy by an average of 8 years.
Pulmonary involvement develops in up to 90% of patients with sarcoidosis. Pulmonary fibrosis occurs in about 20% of these cases, significantly increasing morbidity and mortality. The 10-year mortality rate from diagnosis is around 15%.
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Sources:
- Cottin V., Hirani N. A., Hotchkin D. L. et al. Presentation, diagnosis and clinical course of the spectrum of progressive-fibrosing interstitial lung diseases. Eur Respir Rev 2018; 27 (150): 180076, doi: 10.1183/16000617.0076-2018.
- Češka R. et al. Internal Medicine. 3rd updated edition. Triton, Prague, 2020.
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