Section 4. Lung and Airway Disorders

Chapter 51. Allergic Diseases of the Lungs

Topics: Introduction | Hypersensitivity Pneumonitis | Eosinophilic Pneumonia | Allergic Bronchopulmonary Aspergillosis | Goodpasture's Syndrome

Eosinophilic Pneumonia

Eosinophilic pneumonia (also called pulmonary infiltrates with eosinophilia syndrome) comprises a group of lung diseases in which eosinophils (a type of white blood cell) appear in increased numbers in the lungs and usually in the bloodstream.

Eosinophils participate in the immune response of the lung. The number of eosinophils increases during many inflammatory and allergic reactions, including asthma, which frequently accompanies certain types of eosinophilic pneumonia. Unlike typical pneumonias caused by bacteria, viruses, and most fungi, the tiny air sacs of the lungs (alveoli) are not infected in people with eosinophilic pneumonia. However, the alveoli and often the airways do fill with eosinophils. Even the blood vessel walls may be invaded by eosinophils, and the narrowed airways may become plugged with an accumulation of secretions (mucus) if asthma develops.

The exact reason that eosinophils build up in the lungs is not well understood, and often it is not possible to identify the substance that is causing the allergic reaction. However, there are some known causes of eosinophilic pneumonia, including certain drugs (penicillin, aminosalicylic acid, carbamazepine, naproxen, isoniazid, nitrofurantoin, chlorpropamide, and sulfonamides [such as trimethoprim-sulfamethoxazole]); chemical fumes (nickel inhaled as a vapor); fungi (Aspergillus fumigatus); and parasites (roundworms, including nematodes).

Symptoms and Diagnosis

Symptoms may be mild or life threatening. Simple eosinophilic pneumonia (Löffler's syndrome) and similar pneumonias (such as tropical eosinophilia, which is due to infestation by several species of filariae--types of nematode worms) may produce a slight fever and mild respiratory symptoms, if any. A person may cough, wheeze, and feel short of breath but usually recovers quickly. Another disease known as acute eosinophilic pneumonia may cause the level of oxygen in the blood to decrease severely; it can progress to acute respiratory failure in a few hours or days if not treated.

Chronic eosinophilic pneumonia, which slowly progresses over weeks to months, is a distinct disorder that may also become severe. Life-threatening shortness of breath can develop if the condition is not treated.

With acute eosinophilic pneumonia, tests show large numbers of eosinophils in the blood, sometimes as many as 10 to 15 times the normal number. However, with chronic eosinophilic pneumonia, the numbers of eosinophils in the blood may be normal.

A chest x-ray usually shows white patches in the lungs that are characteristic of pneumonia. However, unlike pneumonia caused by bacteria or viruses, acute eosinophilic pneumonias typically show rapidly appearing and disappearing patches when x-rays are repeated. In contrast, the chest x-ray in chronic eosinophilic pneumonia shows persistent patches located mainly in the outer zones of the lungs.

Microscopic examination of coughed-up sputum or washings of the alveoli obtained during bronchoscopy typically shows clumps of eosinophils. Other laboratory tests may be performed to search for an infection with fungi or parasites; these tests may include microscopic examination of stool specimens. A doctor also considers whether any drug the person is taking may be the cause.

Prognosis and Treatment

Eosinophilic pneumonia may be mild, and people with the disease may get better without treatment. For acute cases, a corticosteroid such as prednisone is usually needed. In chronic eosinophilic pneumonia, prednisone may be needed for many months or even years. If a person develops wheezing, the same treatments used for asthma are given as well (see Section 4, Chapter 44). If worms or other parasites are the cause, the person is treated with appropriate drugs. Ordinarily, drugs that may be causing the illness are discontinued.