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Pulmonary Alveolar Proteinosis

By Joyce Lee, MD, MAS, Assistant Professor, Division of Pulmonary Sciences and Critical Care Medicine, Department of Medicine, University of Colorado Denver

Pulmonary alveolar proteinosis is a rare disorder in which the air sacs of the lungs (alveoli) become plugged with a protein- and fat-rich fluid.

  • Pulmonary alveolar proteinosis typically affects people who are aged 20 to 50 and who have not had lung disease.

  • People have difficulty breathing and cough.

  • Diagnosis is by computed tomography and testing a sample of lung fluid obtained using a bronchoscope.

  • If symptoms are severe, the lungs are washed out, one at a time.

The cause of pulmonary alveolar proteinosis is almost always unknown, but recent studies have linked it to production of an antibody directed against a protein that seems to be involved with the production or the breakdown of surfactant (a substance normally produced in the lungs). Occasionally, development of pulmonary alveolar proteinosis is related to exposure to toxic substances, such as inorganic dusts, infection with Pneumocystis jirovecii, certain cancers, and immunosuppressants. Rarely, it occurs in newborns.

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

When the alveoli are plugged, 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 people have severe difficulty breathing, even at rest. People often have severe disability due to inadequate lung function. Most people also have a cough that often does not produce sputum, but occasionally people expectorate chunky gelatinous material.

Other symptoms may include fatigue, weight loss, and low-grade fever. Lung infections may occur, and this can quickly worsen symptoms of shortness of breath and cause fever.

Diagnosis

  • Chest x-ray and computed tomography

  • Bronchoalveolar lavage

Doctors do several tests, including a chest x-ray and computed tomography (CT) of the chest, and other tests to determine how well the lungs are functioning. A chest x-ray shows evidence of plugging of the alveoli. Computed tomography (CT) shows this plugging and other changes that suggest pulmonary alveolar proteinosis. Pulmonary function testing reveals 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 when the person is at rest. The elimination of carbon dioxide from the lungs may be impaired. Blood test results may show abnormalities that occur in pulmonary alveolar proteinosis as well as in other disorders. For example, levels of some substances (for example, lactic dehydrogenase, red blood cells, serum surfactant proteins, and gamma globulin) are often elevated.

To make a definitive diagnosis of pulmonary alveolar proteinosis, doctors examine a sample of the fluid from the alveoli. To obtain a sample, doctors use a bronchoscope to wash segments of the lung with a salt-water solution and then collect the washings (bronchoalveolar lavage). The washings are often opaque or milky because the fluid is rich in protein and fats. Sometimes doctors obtain a lung tissue sample for microscopic examination (lung biopsy) during bronchoscopy. Occasionally, a larger sample is needed, which must be removed surgically.

Treatment

  • Lung washing

People who have few or no symptoms do not require treatment.

For people with disabling symptoms, the protein- and fat-rich fluid in the alveoli can be washed out with a salt solution during bronchoscopy or through a special tube inserted through the mouth or through the windpipe (trachea) and into one lung. This procedure is called a lung lavage. 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 after the person has been given general anesthesia. One washing is enough for some people, but others need washings every 6 to 12 months for many years.

Recombinant granulocyte-macrophage colony stimulating factor, a substance that stimulates the body's production of white blood cells, may be given by inhalation or subcutaneous injection.

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.

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