Idiopathic pulmonary fibrosis (IPF), the most common form of idiopathic interstitial pneumonia, causes progressive pulmonary fibrosis. Symptoms and signs develop over months to years and include exertional dyspnea, cough, and fine (Velcro) crackles. Diagnosis is based on history, physical examination, high-resolution CT, and/or lung biopsy, if necessary. Pirfenidone is available for treatment in some countries. Most patients deteriorate; median survival is about 3 yr from diagnosis.
IPF, identified histologically as usual interstitial pneumonia, accounts for most cases of idiopathic interstitial pneumonia (see Overview of Idiopathic Interstitial Pneumonias). IPF affects men and women > 50 in a ratio of 2:1, with a markedly increased incidence with each decade of age. Current or former cigarette smoking is most strongly associated with the disorder. There is some genetic predisposition; familial clustering occurs in up to 20% of cases.
A combination of environmental, genetic, and other unknown factors probably contribute to alveolar epithelial cell dysfunction or reprogramming, which leads to abnormal fibroproliferation in the lung. There is ongoing research into the contributions of genetics, environmental stimuli, inflammatory cells, the alveolar epithelium, mesenchyme, and matrix.
The key histologic findings are subpleural fibrosis with sites of fibroblast proliferation (fibroblast foci) and dense scarring, alternating with areas of normal lung tissue (heterogeneity). Scattered interstitial inflammation occurs with lymphocyte, plasma cell, and histiocyte infiltration. Cystic abnormality (honeycombing) occurs in all patients and increases with advanced disease. A similar histologic pattern uncommonly occurs in cases of interstitial lung diseases of known etiology (see Table 2: Key Features of Idiopathic Interstitial Pneumonias).
Symptoms and Signs
Symptoms and signs typically develop over 6 mo to several years and include dyspnea on exertion and nonproductive cough. Constitutional symptoms, such as low-grade fever and myalgias, are uncommon. The classic sign of IPF is fine, dry, inspiratory crackles (Velcro crackles) at both bases. Clubbing is present in about 50% of cases. The remainder of the examination is normal until disease is advanced, at which time signs of pulmonary hypertension and right ventricular systolic dysfunction may develop.
Diagnosis is suspected in patients with subacute dyspnea, nonproductive cough, and Velcro crackles on chest examination. However, IPF is commonly overlooked initially because of clinical similarities to other more common diseases, such as bronchitis, asthma, and heart failure. Diagnosis requires HRCT and in some cases surgical lung biopsy.
Chest x-ray typically shows diffuse reticular opacities in the lower and peripheral lung zones. Small cystic lesions (honeycombing) and dilated airways due to traction bronchiectasis are additional findings.
HRCT shows diffuse, patchy, subpleural, reticular opacities with irregularly thickened interlobular septa and intralobular lines; subpleural honeycombing; and traction bronchiectasis. Ground-glass opacities affecting > 30% of the lung suggest an alternative diagnosis.
Laboratory testing plays little role in diagnosis.
Most patients have moderate to advanced clinical disease at the time of diagnosis and deteriorate despite treatment. Median survival is about 3 yr from time of diagnosis. Several prognostic models have been proposed. Among the factors that portend a worse prognosis are older age, male sex, lower forced vital capacity, and lower DLco.
Causes of acute deterioration include infections, pulmonary embolism, pneumothorax, and heart failure. Also, acute exacerbations without an identifiable cause may occur. All acute exacerbations have a high morbidity and mortality. Lung cancer occurs more frequently in patients with IPF, but cause of death is usually respiratory failure. Because of the poor prognosis of IPF, early discussions with the patient and family about advance care planning and end-of-life care are important (see Advance Directives).
Pirfenidone, a new antifibrotic drug available in some countries, may slow disease progression. It is under study. Supportive measures include O2 and pulmonary rehabilitation. Patients may find that joining a support group helps reduce the stress of the illness.
Many novel therapies for IPF are under development or being tested as treatments for IPF, and patients should be encouraged to participate in clinical trials when appropriate.
Lung transplantation is successful for otherwise healthy IPF patients, generally those < 65 yr old. Otherwise healthy IPF patients should be evaluated for lung transplantation at the time of diagnosis.
Last full review/revision April 2013 by Harold R. Collard, MD
Content last modified November 2013