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Löffler syndrome, also known as simple pulmonary eosinophilia, is a transient, self-limited pulmonary condition characterized by:

It often represents the pulmonary phase of parasitic infections, particularly those with tissue migration through the lungs.

Etiology

Category Common Causes
Parasitic infections Most common: Ascaris lumbricoides
Other: Strongyloides, hookworm (Ancylostoma, Necator), Toxocara
Drug-induced (rare) NSAIDs, antibiotics, anticonvulsants
Idiopathic Occasionally no clear cause is found

Pathophysiology

Clinical Features

Feature Details
Symptoms Often asymptomatic or mild; may include dry cough, dyspnea, wheeze
Fever Mild or absent
Timing Appears 7–14 days after larval ingestion or exposure
Peripheral eosinophilia Present, typically <1000–1500/μL, but may be higher
Duration Self-resolves in <1 month, usually within 7–10 days

Radiology

Modality Imaging features
CXR • Transient non-segmental peripheral patchy opacities
• Migratory infiltrates (HALLMARK): Lesions resolve and reappear in other zones
• No volume loss or effusion (helps distinguish from pneumonia or edema)
HRCT • Peripheral or subpleural ground-glass opacities
• Non-lobar, migratory ill-defined consolidations
• No architectural distortion (confirms acute and reversible nature)
• No lymphadenopathy/pleural effusion (supports diagnosis over other eosinophilic lung diseases)

![Boy with mild fever, cough, and blood eosinophilia of 60%; diagnosis was simple pulmonary eosinophilia: A, Initial frontal chest radiograph shows dominant peripheral opacity in left middle lung zone. B, Follow-up frontal chest radiograph 13 days after A shows interval improvement in left middle lung zone opacity and newly developed bilateral lesions

Bernheim A, McLoud T. A review of clinical and imaging findings in eosinophilic lung diseases. American Journal of Roentgenology. 2017;208(5):1002-1010. doi:10.2214/ajr.16.17315](attachment:8771e062-dab3-4486-8e9c-efd05e5e7895:image.png)

Boy with mild fever, cough, and blood eosinophilia of 60%; diagnosis was simple pulmonary eosinophilia: A, Initial frontal chest radiograph shows dominant peripheral opacity in left middle lung zone. B, Follow-up frontal chest radiograph 13 days after A shows interval improvement in left middle lung zone opacity and newly developed bilateral lesions

Bernheim A, McLoud T. A review of clinical and imaging findings in eosinophilic lung diseases. American Journal of Roentgenology. 2017;208(5):1002-1010. doi:10.2214/ajr.16.17315

![Simple pulmonary eosinophilia in a 32-year-old woman with migratory opacities. (A) Initial chest radiograph shows bilateral multifocal consolidation. (B) CT demonstrates multifocal consolidation and ground-glass opacities. (C) Repeat chest radiograph 2 weeks later shows bilateral consolidation in a different distribution.

Price M, Gilman MD, Carter BW, Sabloff BS, Truong MT, Wu CC. Imaging of eosinophilic lung diseases. Radiologic Clinics of North America. 2016;54(6):1151-1164. doi:10.1016/j.rcl.2016.05.008](attachment:3617add8-90fd-4a85-90d2-bb575d2d587a:image.png)

Simple pulmonary eosinophilia in a 32-year-old woman with migratory opacities. (A) Initial chest radiograph shows bilateral multifocal consolidation. (B) CT demonstrates multifocal consolidation and ground-glass opacities. (C) Repeat chest radiograph 2 weeks later shows bilateral consolidation in a different distribution.

Price M, Gilman MD, Carter BW, Sabloff BS, Truong MT, Wu CC. Imaging of eosinophilic lung diseases. Radiologic Clinics of North America. 2016;54(6):1151-1164. doi:10.1016/j.rcl.2016.05.008

Differentials