Merck Manual

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Löffler Syndrome


Joyce Lee

, MD, MAS, University of Colorado Denver

Last full review/revision Sep 2019| Content last modified Sep 2019
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Löffler syndrome is a form of eosinophilic pulmonary disease characterized by absent or mild respiratory symptoms (most often dry cough), fleeting migratory pulmonary opacities, and peripheral blood eosinophilia.

Parasitic infections, especially ascariasis, may be the cause, but an identifiable etiologic agent is not found in up to one third of patients.

The diagnosis of Löffler syndrome is based on characteristic and often transient respiratory symptoms, chest x-ray findings, and peripheral blood eosinophilia. It requires the exclusion of other types of eosinophilic lung disease. For example, acute eosinophilic pneumonia is a distinct entity with acute onset, severe hypoxemia, and typically a lack of increased blood eosinophils at the onset of disease.

The disease usually resolves within 1 month.

Treatment of Löffler syndrome is symptomatic and may consist of corticosteroids.

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