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Eosinophilic Pneumonia

By Harold R. Collard, MD, Associate Professor, Department of Medicine, University of California San Francisco

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.

  • Certain disorders, drugs, chemicals, fungi, and parasites may cause eosinophils to accumulate in the lungs.

  • People may cough, wheeze, or feel short of breath, and some people develop respiratory failure.

  • Doctors use x-rays and laboratory tests to detect the disorder and determine the cause, especially if parasites are suspected as the cause.

  • Corticosteroids are usually given.

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. Eosinophilic pneumonia differs from typical pneumonias in that there is no suggestion that the tiny air sacs of the lungs (alveoli) are infected by bacteria, viruses, or fungi. 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 accumulate in the lungs is not well understood, but it may be a type of allergic reaction. 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

  • Cigarette smoke

  • Certain drugs (for example, penicillin, aminosalicylic acid, carbamazepine, l-tryptophan, naproxen, isoniazid, nitrofurantoin, phenytoin, chlorpropamide, and sulfonamides [such as trimethoprim/sulfamethoxazole])

  • Chemical fumes (for example, cocaine or nickel inhaled as a vapor)

  • Fungi (typically Aspergillus fumigatus)

  • Parasites (particularly roundworms, including nematodes)

  • Disorders (for example, eosinophilic granulomatosis with polyangiitis [formerly Churg-Strauss syndrome])


Symptoms may be mild or life threatening, and acute or chronic.

Acute eosinophilic pneumonia progresses quickly. It may cause fever, chest pain worsened by deep breathing, shortness of breath, cough, and a general feeling of illness. The level of oxygen in the blood can decrease severely, and acute eosinophilic pneumonia can progress to acute respiratory failure in a few hours or days if not treated. Löffler syndrome, often part of an infestation by any of several species of nematode worms called filaria, may cause mild respiratory symptoms, if any. A person may cough, wheeze, and feel short of breath but usually recovers quickly.

Chronic eosinophilic pneumonia, which slowly progresses over days or weeks, is a distinct disorder that may also become severe. It tends to remit and recur on its own and may worsen over weeks or months. Life-threatening shortness of breath can develop if the condition is not treated.


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

A chest x-ray is abnormal in acute eosinophilic pneumonia, but similar abnormalities can occur in other conditions. The chest x-ray is more effective for diagnosis of chronic eosinophilic pneumonia. In both cases, but particularly in the acute form, computed tomography (CT) is often more effective for diagnosis.

Microscopic examination of cells from washings of the alveoli obtained during bronchoscopy typically shows clumps of eosinophils. Other laboratory tests may be done to search for an infection with fungi or parasites. These tests may include microscopic examination of stool specimens to look for worms and other parasites.

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 Asthma : Treatment). If worms or other parasites are the cause, the person is treated with appropriate drugs. Ordinarily, drugs that may be causing the illness are stopped.

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