Allergic Bronchopulmonary Aspergillosis

Allergic bronchopulmonary aspergillosis is an allergic lung disorder that often mimics pneumonia and is characterized by asthma, airway and lung inflammation with eosinophils (a type of white blood cell), and increased numbers of eosinophils in the blood.

Allergic bronchopulmonary aspergillosis is caused by an allergic reaction to a fungus, most commonly Aspergillus fumigatus. This fungus flourishes in soil, decaying vegetation, foods, dusts, and water. A person who inhales the fungus may become sensitized and develop allergic asthma. Other fungi, including Penicillium, Candida, Curvularia, and Helminthosporium, can cause an identical illness. In some people, a more complex allergic reaction can develop in 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 lungs or directly destroy tissue. The fungus does colonize the asthmatic mucus in the airways and causes recurrent allergic inflammation in the lung. The tiny air sacs of the lungs (alveoli) become packed primarily with eosinophils. Increased numbers of mucus-producing cells may also appear. In advanced cases, inflammation may cause the central airways to widen permanently, a condition called bronchiectasis (see Section 4, Chapter 47). 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. The fungus can also form a fungus ball, called an aspergilloma, in cavities and cysts of lungs already damaged by another disease, such as tuberculosis. The major consequence of such fungus balls is lung bleeding, often severe, which becomes apparent when the person coughs up blood and is short of breath.

Symptoms and Diagnosis

The first indications of allergic bronchopulmonary aspergillosis are usually progressive symptoms of asthma, such as wheezing and shortness of breath, and a mild fever. The person usually does not feel well. Brownish flecks or plugs may appear in coughed-up sputum.

Repeated chest x-rays show areas that look like pneumonia, but they move around, most often in the upper parts of the lungs. With long-standing disease, chest x-rays or computed tomography (CT) may show widened airways often plugged with mucus. The fungus itself, along with excess eosinophils, may be seen when the sputum is examined under the microscope. Blood tests reveal high levels of eosinophils and antibodies to Aspergillus. 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, which may occur in people who have allergic asthma without aspergillosis.

Treatment

Because Aspergillus appears in many places in the environment, the fungus is difficult to avoid. Antiasthma drugs, especially corticosteroids, are used to treat allergic bronchopulmonary aspergillosis (see Section 4, Chapter 44). Antiasthma drugs also 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 over a long period of time in lower doses may prevent progressive lung damage. Most specialists recommend oral corticosteroids; the inhaled kind has not been shown to work well for this condition. The antifungal drug itraconazole may be helpful. Allergy shots (desensitization) may cause complications and are not recommended.

Because the lung damage may worsen without causing any noticeable symptoms, a doctor regularly monitors the person using chest x-rays, pulmonary function tests (see Section 4, Chapter 39), and antibody measurements of immunoglobulin E (IgE) and other immunoglobulins. As the disease is controlled, the antibody levels usually fall, but they may rise again as an early sign of flare-ups.