Pulmonary Alveolar Proteinosis
Pulmonary alveolar proteinosis is a rare disease in which the air sacs of the lungs (alveoli) become plugged with a protein-rich fluid.
The disease generally affects people between the ages of 20 and 60 who have not previously had lung disease. The cause of pulmonary alveolar proteinosis is unknown. Occasionally, it is related to exposure to toxic substances, such as inorganic dusts, infection with Pneumocystis carinii (see Section 4, Chapter 42), certain cancers, and immunosuppressant drugs.
The protein in the lungs plugs up the alveoli and small airways. In rare instances, lung tissue becomes scarred. The disease may progress, remain stable, or disappear spontaneously.
Symptoms and Diagnosis
When the alveoli are plugged up, the transfer of oxygen to the blood from the lungs is severely impaired. Consequently, most people with pulmonary alveolar proteinosis experience shortness of breath when they exert themselves. Some have severe difficulty breathing, even at rest. Most also have a cough that does not usually produce sputum unless they are smokers. People often have severe disability from inadequate lung function. Lung infections may quickly worsen symptoms of shortness of breath and produce fever.
A chest x-ray shows extensive dense white patches in both lungs, usually located centrally near the heart. Computed tomography (CT) shows similar and other changes that suggest the disease. Pulmonary function tests (see Section 4, Chapter 39) reveal that the volume of air that the lungs can hold is abnormally small. Tests show low levels of oxygen in the blood, at first only during exercise but later also at rest. Even breathing pure oxygen results in well below the expected level of oxygen in the blood. Blood test results are not specific, although levels of some substances (for example, lactic dehydrogenase [LDH] and gamma globulin levels) are often elevated.
To make a definitive diagnosis, a doctor examines a sample of the fluid from the alveoli. To obtain a sample, a doctor uses a bronchoscope (see Section 4, Chapter 39) to wash segments of the lung with a salt solution and then collects the washings. Sometimes a doctor performs a lung biopsy (obtains a lung tissue sample for microscopic examination) during bronchoscopy. Occasionally, a larger specimen is needed, which must be removed surgically.
Treatment
People who have few or no symptoms do not require treatment. For those with disabling symptoms, the protein-rich fluid in the alveoli can be washed out with a salt solution during bronchoscopy or through a special tube inserted through the mouth into or through the windpipe (trachea). Sometimes only a small section of the lung must be washed, but if symptoms are severe and the levels of oxygen in the blood are very low, the person is given general anesthesia, so that one entire lung can be washed. About 3 to 5 days later, the other lung is washed, again with the person under general anesthesia. One washing is enough for some people, while others need washings every 6 to 12 months for many years.
The usefulness of other treatments, such as potassium iodide and enzymes that break up proteins, is unclear. Corticosteroids, such as prednisone, are not effective and may actually increase the chance of infection. Bacterial infections are treated with antibiotics, usually taken by mouth.
Some people with pulmonary alveolar proteinosis are short of breath indefinitely, but the disease is rarely fatal as long as they have regular lung washings.
 See the table Unusual Infiltrative Lung Diseases.
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