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Allergic Bronchopulmonary Aspergillosis
Allergic bronchopulmonary aspergillosis is an allergic lung reaction to a type of fungus (most commonly Aspergillus fumigatus) that occurs in some people with asthma or cystic fibrosis.
The fungus Aspergillus fumigatus flourishes in soil, decaying vegetation, foods, dusts, and water. Certain people who inhale the fungus may become sensitized and develop a chronic allergic reaction. Other fungi, including Penicillium, Candida, Curvularia, and Helminthosporium, can cause an identical illness. In some people, the effects of the allergic reaction combine with the effects of the fungus to damage the airways and lungs.
The disorder differs from typical pneumonias caused by bacteria, viruses, and most fungi, in that the fungus does not actually invade the lung tissue and directly destroy it. The fungus colonizes the mucus in the airways of people with asthma or cystic fibrosis (both of whom tend to have increased amounts of mucus) and causes recurrent allergic inflammation in the lung. The tiny air sacs of the lungs (alveoli) become packed primarily with eosinophils (a type of white blood cell). Increased numbers of mucus-producing cells may also appear. If the disease has caused extensive damage, inflammation may cause the central airways to widen permanently, a condition called bronchiectasis (see Bronchiectasis). Eventually, the lungs are likely to become scarred.
Other forms of aspergillosis can occur. Aspergillus can invade the lungs and cause serious pneumonia in people with an impaired immune system. This condition is an infection, not an allergic reaction (see Aspergillosis). Aspergillus can also form fungus balls (aspergillomas) in cavities and cysts of lungs damaged by another disease, such as tuberculosis; severe bleeding may result.
Repeated chest x-rays show areas that look like pneumonia, but they appear to persist or migrate to new areas of the lung, most often in the upper parts. In people with long-standing disease, chest x-rays or computed tomography (CT) may show widened airways, which are often plugged with mucus.
The fungus itself, along with excess eosinophils, may be seen when a sputum sample is examined under a microscope.
Blood tests reveal high levels of eosinophils and antibodies to Aspergillus. The level of immunoglobulin E (an antibody) in the blood is also measured because elevated levels of IgE often indicate an allergic response.
Skin testing can determine if the person is allergic to Aspergillus, but the test does not distinguish between allergic bronchopulmonary aspergillosis and a simple allergy to Aspergillus. A simple allergy to Aspergillus may occur in people who have asthma.
Because Aspergillus is present in many places in the environment, the fungus is difficult to avoid. Drugs used in the treatment of asthma, especially corticosteroids, are used to treat allergic bronchopulmonary aspergillosis (see Table: Drugs Commonly Used to Treat Asthma). Drugs (bronchodilators) may be used to open up the airways, making it easier to cough up mucus plugs and clear out the fungus. The corticosteroid prednisone, taken initially in high doses, and then over a long period of time in lower doses, may prevent progressive lung damage. Most specialists recommend oral corticosteroids. Inhaled corticosteroids have not been shown to work well for this condition.
The antifungal drug itraconazole is sometimes used in addition to corticosteroids to help eliminate the fungus from the lung.
Because the lung damage may worsen gradually without causing any noticeable changes in symptoms, chest x-rays, pulmonary function tests (see Pulmonary Function Testing (PFT)), levels of eosinophils in the blood, and amounts of IgE antibody are regularly monitored. As the disease is controlled, the eosinophil and antibody levels usually fall, but they may rise again as an early sign of flare-ups.
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