Introduction
Idiopathic pulmonary fibrosis (IPF) is a rare progressive disorder that affects the respiratory system. It is characterized by scarring and thickening of the lung tissues, which makes it difficult to transport oxygen effectively into the bloodstream. Idiopathic pulmonary fibrosis usually affects elderly people aged between 50 and 70. IPF belongs to the group of lung conditions called interstitial lung diseases (ILD).
What Are the Signs and Symptoms of Idiopathic Pulmonary Fibrosis?
The signs and symptoms of idiopathic pulmonary fibrosis are:
-
Progressive exertional dyspnea (shortness of breath during physical activity).
-
Persistent hacking dry cough (cough without mucus production).
-
Leg swelling.
-
Loss of appetite.
-
Chest pain.
-
Clubbing of the digits (bulging of fingertips).
-
Fatigue (tiredness).
-
Weight loss.
What Are the Risk Factors of Idiopathic Pulmonary Fibrosis?
The risk factors of idiopathic pulmonary fibrosis include:
-
Age - Common in elderly people aged above 50.
-
Gender - More common in men than women.
-
Genetics - Mutation in genes such as TERC (telomerase RNA component) and TERT (telomerase reverse transcriptase).
Other risk factors are:
-
Acid reflux disease (backward flow of the stomach acid to the mouth through a food pipe).
-
Inhalation of metal, silica, or wood dust.
-
Viral infections.
-
Certain medications.
What Are the Differential Diagnoses of Idiopathic Pulmonary Fibrosis?
The differential diagnoses of idiopathic pulmonary fibrosis include:
-
Connective tissue disorder (a disease that affects the connecting structures of the body such as blood vessels, bone, cartilage, etc.).
-
Hypersensitivity pneumonitis (a lung disease in which there is a swelling of the lung tissues due to inhalation of fungus, dust, or molds).
-
Asbestosis (a lung disease caused by inhalation of asbestos fibers).
-
Drug-induced lung disease.
What Are the Diagnostic Criteria Used in the Diagnosis of Idiopathic Pulmonary Fibrosis?
Diagnostic Criteria of 2000:
Major Criteria:
-
All known causes of (ILD) interstitial lung diseases such as medication, systemic disease, environmental exposure, and idiopathic interstitial pneumonia are excluded.
-
Abnormal lung function studies such as reduced vital capacity and impaired gas exchange.
-
Bronchoalveolar lavage (BAL) or transbronchial lung biopsy (TBB) shows no supporting features for an alternative diagnosis.
-
High-resolution computed tomography (HRCT) showed ground glass opacity and bibasilar reticular abnormalities.
Minor Criteria:
-
Age more than 50 years old.
-
Unexplained dyspnoea on exertion.
-
The duration of the disease for three or greater than three months period.
-
Bibasilar crackles (velcro-like).
Diagnostic Criteria of 2011:
The American thoracic society (ATS), the Japanese respiratory society (JRS), the European respiratory society (ERS), and the Latin-American thoracic society (ALAT) provide guidance for the management and diagnosis of idiopathic pulmonary fibrosis. This criterion is enough to diagnose IPF by eliciting other differential diagnoses.
-
Exclusion of all the known causes of interstitial lung disease (ILD), such as environmental exposure, connective tissue diseases, and drug toxicity.
-
Presence of UIP (usual interstitial pneumonia) pattern on HRCT scan in patients who are not subjected to surgical lung biopsy (SLB).
-
Specific combinations of surgical lung biopsy pattern (SLB) and HRCT in individuals subjected to SLB.
What Are the Imaging Techniques Used in the Diagnosis of Idiopathic Pulmonary Fibrosis?
The imaging techniques used in the diagnosis of idiopathic pulmonary fibrosis include:
Chest Radiography:
-
In the early stages of idiopathic pulmonary fibrosis, chest radiography shows small interstitial shadowing of about 1 to 2 millimeters, irregular opacities in about 75 percent of patients, and small, round opacities in about 20 percent of patients (reticulonodular opacities).
-
Septal lines and peripheral attenuation are also seen.
-
One of the common features is hazy, diffuse, or patchy ground glass opacity.
-
In 60 percent of patients, raised diaphragm and volume loss were accompanied by basal discoid atelectasis.
-
Pneumomediastinum (collection of air between the lungs and the chest wall) and pneumothorax (collection of air between the lung and the chest wall) are seen in some patients.
-
When the alveolitis progresses to fibrosis, the fine line becomes coarse, and there might be small cysts measuring about 2 millimeters.
-
Honeycombing refers to the clustering of cystic air spaces with well-defined margins that range from 0.3 to 1 centimeter and, in rare cases, 2.5 centimeters.
-
These cysts combine together to form a larger cyst of diameter 5 to 7 millimeters, which appears as ring-shaped opacity inside the honeycomb lung.
-
In the later stage, the fibrosis becomes worse and honeycombing becomes coarser, and there is a further volume loss.
-
In the advanced stages, chest radiography shows the features of pulmonary arterial hypertension.
Computed Tomography (CT) Scan:
-
In high-resolution computed tomography (HRCT), the end-stage IPF appears honeycombing without ground glass appearance. These findings on HRCT eliminates the risk of invasive diagnostic procedures such as lung biopsy.
-
In the active stage, HRCT shows ground-glass attenuation and acute alveolitis, which is reversible and can be treated.
-
The end stage of IPF is irreversible and difficult to treat.
-
The hallmark finding of interstitial lung disease is an interstitial B line which appears as vertical and hyperechoic.
-
An irregular, thick fragmented pleura line associated with subpleural fibrotic scars is seen.
-
The number of interstitial B lines depends on the severity and extension of pulmonary fibrosis on high-resolution computed tomography (HRCT). The distance between two adjacent interstitial B lines indicates a pure reticular fibrotic pattern.
-
Subpleural periphery and bibasilar reticular opacity are commonly seen in IPF, and their distribution is more in the posterior aspect. It is generally associated with traction bronchiectasis and subpleural honeycombing.
When Does Surgical Lung Biopsy Perform?
Tissue samples are taken from two or three lobes to detect the histopathological findings as high variability in morphology and distribution of idiopathic pulmonary fibrosis. It is important to evaluate the potential risks before performing a surgical lung biopsy (SLB) as the procedure outweighs the benefits, especially in elderly patients, impaired pulmonary function tests, and associated medical conditions such as heart failure and pulmonary hypertension. In recent days cryo-biopsy has shown effective results as it is less invasive than surgical lung biopsy and also replaces surgical lung biopsy in obtaining tissue samples.
What Are the Complications of Idiopathic Pulmonary Fibrosis?
The complications of idiopathic pulmonary fibrosis include:
-
Pulmonary hypertension (a condition in which increased blood pressure affects the arteries of the lungs and the heart).
-
Acute exacerbation of pulmonary fibrosis (scarring of the lung tissues).
-
Thromboembolic disease (blockage of the blood vessels due to blood clot).
-
Lung cancer.
-
Adverse drug effects.
-
Pulmonary emboli (a condition in which a blood clot blocks the arteries of the lungs).
-
Pneumonia (a lung infection that causes swelling of the air sacs of the lungs).
Conclusion
In idiopathic pulmonary fibrosis, a high-resolution computed tomography (HRCT) scan predicts the outcome and guides the treatment well, as the findings in HRCT show a correlation with the histological pattern of idiopathic pulmonary fibrosis. The accuracy of HRCT in diagnosing IPF is greater when compared to chest radiography. The pulmonary function test in IPF shows a restrictive pattern along with decreased diffusing capacity. Serological investigation such as an antinuclear antibody (ANA), anti-cyclic citrullinated peptide, and rheumatoid factor (RF) is essential to distinguish idiopathic pulmonary fibrosis from connective tissue disorders.
