Idiopathic Pulmonary Fibrosis
Idiopathic pulmonary fibrosis is a specific form of pulmonary fibrosis; the cause is unknown.
In about half of the people who have pulmonary fibrosis, the cause is never identified. These people are said to have idiopathic pulmonary fibrosis. The word idiopathic means "of unknown cause."
In idiopathic pulmonary fibrosis, the lungs suffer repeated episodes of injury for a long period of time. The injury causes chronic inflammation that eventually leads to pulmonary fibrosis.
Symptoms and Diagnosis
Symptoms depend on the extent of the lung damage, the rate at which the disease progresses, and the development of complications, such as lung infections and cor pulmonale (see Section 4, Chapter 54). The main symptoms start insidiously as shortness of breath on exertion, cough, and diminished stamina. Common symptoms include weight loss and fatigue. In most people, symptoms worsen over several years.
Late in the disease, as the level of oxygen in the blood decreases, the skin may take on a bluish tinge (called cyanosis), and the ends of the fingers may become thick or club-shaped (see Section 4, Chapter 39). Strain on the heart may cause the right ventricle to enlarge, eventually resulting in cor pulmonale. Through a stethoscope, a doctor often hears crackling sounds. These sounds are called Velcro crackles or rales, described as such because the sound is similar to that of Velcro when it is pulled apart.
A chest x-ray may show widespread tiny white lines, often in a netlike pattern, most profuse in the lower parts of both lungs. Computed tomography (CT) is more sensitive than a chest x-ray for detecting disease early and helps the doctor make a more specific diagnosis. Typically the CT shows a pattern of patchy, white lines in the lower lungs. In areas of more severe involvement, the thick scarring often creates a honeycombing appearance. Pulmonary function tests (see Section 4, Chapter 39) show that the amount of air the lungs can hold is below normal. Analysis of a blood sample shows a low level of oxygen with minimal exercise (walking at a normal pace) and, as the disease progresses, even when the person is resting.
To confirm the diagnosis, a doctor may perform a lung biopsy (removal of a small piece of lung tissue for microscopic examination) using a procedure called bronchoscopy (see Section 4, Chapter 39). Many times, a larger tissue specimen is needed and must be removed surgically, sometimes with use of a thoracoscope (see Section 4, Chapter 39).
Blood tests cannot confirm the diagnosis but are performed as part of the search for other diseases that may cause a similar pattern of inflammation and scarring. Doctors perform other blood tests to screen for certain autoimmune disorders.
Doctors may also perform other tests (for example, an electrocardiogram or echocardiogram) to identify if any changes in the heart have resulted from the lung disease.
Treatment and Prognosis
If a chest x-ray or lung biopsy shows that scarring is not extensive, the usual treatment is a corticosteroid, such as prednisone. A doctor evaluates the person's response using chest x-rays, CT, and pulmonary function tests. High doses of prednisone are usually given for about 3 months; then the dose is gradually reduced for another 3 months. Much lower doses are then continued for 6 more months. A few people who are not helped by prednisone may improve with azathioprine or cyclophosphamide. Unfortunately, treatment with corticosteroids fails to help most people. One promising treatment is interferon gamma-1b, which appears to block scar formation in the lungs.
Other treatments are aimed at relieving symptoms: oxygen therapy for low blood oxygen levels, antibiotics for infection, and drugs for the heart failure that is produced by cor pulmonale. Lung transplantation (often with a single lung) has been successful in some people with severe idiopathic pulmonary fibrosis.
The prognosis varies greatly. Most people continue to get worse. On average, people live 4 to 6 years after diagnosis. Some survive for many years; a few die within several months.
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