Atlas of pathophysiology, 2 Edition
Part II - Disorders
Idiopathic Pulmonary Fibrosis
Idiopathic pulmonary fibrosis is a chronic and usually fatal interstitial pulmonary disease. Once thought to be a rare condition, it's now diagnosed with much greater frequency. Survival is estimated at 3 to 5 years after diagnosis. Idiopathic pulmonary fibrosis has been known by several other names over the years, including cryptogenic fibrosing alveolitis, diffuse interstitial fibrosis, idiopathic interstitial pneumonitis, and Hamman-Rich syndrome.
Idiopathic pulmonary fibrosis occurs most commonly in people between ages 50 and 70.
Idiopathic pulmonary fibrosis reflects the accumulation of excessive fibrous or connective tissue in the lung parenchyma. It's the result of a cascade of inflammatory, immune, and fibrotic processes in the lung. Despite many studies, the stimulus that begins the progression remains unknown. Speculation has revolved around viral and genetic causes, but no good evidence has been found to support either theory. However, it's clear that chronic inflammation plays an important role. Inflammation develops the injury and the fibrosis that ultimately distorts and impairs the structure and function of the alveolocapillary gas exchange surface. The lungs become stiff and difficult to ventilate, and the diffusion capacity of the alveolocapillary membrane decreases, leading to hypoxemia.
Signs and symptoms
· Dyspnea and rapid, shallow breathing
· Dry, hacking cough
· End-expiratory crackles and bronchial breath sounds
· Clubbed fingers and toes
· Pulmonary hypertension
· Profound hypoxemia and severe, debilitating dyspnea in advanced disease
· Chest pain
Diagnostic test results
Diagnosis begins with a thorough patient history to exclude any of the more common causes of interstitial lung disease, such as:
· environmental or occupational exposure—coal dust, asbestos, silica, beryllium
· connective tissue diseases—scleroderma, rheumatoid arthritis
· drug use—amiodarone, tocainide, crack cocaine.
Tests that help to confirm the diagnosis include:
· lung biopsy—shows mixed areas of normal tissue, interstitial inflammation, fibrosis, and honeycombing
· chest X-ray and high-resolution computed tomography—show a pattern of diffuse interstitial lung disease, with fibrosis and honeycombing
· pulmonary function tests—reveal decreased total lung volumes.
· Oxygen therapy
· Immunosuppressants, such as cyclophosphamide and azathioprine
· Pulmonary rehabilitation
· Lung transplantation
Because idiopathic pulmonary fibrosis generally responds poorly to treatment and because drug therapies cause so many adverse reactions, research studies are currently aimed at learning which factors may improve the patient's response to treatment. The chances of a positive response to therapy and extended survival seem to be best for young female patients with less-than-average dyspnea and hypoxemia, more normal lung function, and no history of smoking. Evidence of inflammation (lymphocytes in bronchoalveolar lavage fluid, circulating immune complexes, and positive response to corticosteroids) also seems to predict a better outcome. Indicators of a poor prognosis are irreversible lung destruction and fibrosis (severe hypoxemia, decreased diffusing capacity for carbon monoxide, and neutrophils and eosinophils in bronchoalveolar lavage fluid).