Loefflers pulmonary eosinophilia

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Loeffler syndrome pulmonary eosinophilia

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Loeffler's Pulmonary Eosinophilia (Loeffler Syndrome / Simple Pulmonary Eosinophilia)

Definition and Historical Context

Loeffler first described this syndrome in 1932 as a transient, self-limited clinical condition characterized by three core features:

Mild respiratory symptoms
Peripheral blood eosinophilia
Migratory ("fleeting") pulmonary infiltrates

The term "simple pulmonary eosinophilia" is used interchangeably. A classification was formally proposed in 1952 by Crofton and colleagues after reviewing 450 cases in the literature. In the broader scheme of eosinophilic pneumonias, Loeffler syndrome sits in the category of known-cause, acute-onset eosinophilic pneumonia without extrapulmonary manifestations (see diagnostic algorithm below).

Diagnostic algorithm for eosinophilic pneumonia

Loeffler syndrome: no extrapulmonary features, identifiable cause (parasitic), acute onset - Murray & Nadel's Textbook of Respiratory Medicine

Etiology

The primary mechanism is transpulmonary larval migration of helminths. The most common causative agents include:

Organism	Route of Infection	Geographic Notes
Ascaris lumbricoides (roundworm)	Ingestion of ova	Most common; now rare in Western countries
Ascaris suum	Ingestion	Zoonotic
Ancylostoma duodenale, Necator americanus (hookworms)	Skin penetration through feet	Southeastern USA, Mexico, Central/South America
Strongyloides stercoralis	Skin penetration	Widely endemic
Trichinella spiralis	Ingestion of undercooked meat	Rare
Toxocara canis (dog roundworm)	Soil ingestion (visceral larva migrans)	Children most affected

The term has also been broadened to encompass drug-induced and toxin-induced pulmonary eosinophilia with a similar transient picture. A majority of Loeffler's original cases were likely due to Ascaris lumbricoides, though Ascaris causes Loeffler syndrome in only a small minority of infected individuals.

Fishman's Pulmonary Diseases and Disorders, 2-Volume Set

Pathogenesis

Following ingestion of Ascaris ova, larvae hatch in the small intestine, cross the intestinal wall, enter the splanchnic and then pulmonary circulation, and migrate across pulmonary capillaries into alveoli. This transpulmonary passage triggers acute eosinophilic inflammation, which resolves once the larvae ascend the airways and descend into the alimentary tract to complete their life cycle. The entire larval lung transit is the mechanistic driver of symptoms.

Key cytokines mediating eosinophil recruitment to the lung:

IL-5 (primary) - drives eosinophil differentiation, maturation, tissue recruitment, and survival
GM-CSF, IL-3, IL-33 (secondary)
Chemokines: eotaxins (CCL11, CCL24, CCL26), LTB4
Fishman's Pulmonary Diseases and Disorders

Clinical Features

Loeffler syndrome affects all age groups. Symptoms are generally mild and self-limited, resolving within 1-2 weeks:

Low-grade fever
Nonproductive cough
Mild to occasionally severe dyspnea
Chest discomfort on coughing or deep breathing
Wheezing
Occasional hemoptysis
Urticaria or skin lesions (especially with hookworm - "creeping eruption": raised, erythematous, serpiginous, tunnel-like, pruritic skin lesion)

Hookworm ("creeping eruption") causes Loeffler syndrome in up to 50% of cases.

Diagnostic Studies

Peripheral blood:

Moderate to extreme eosinophilia (often peak at time of respiratory symptoms)

Stool examination:

Negative for ova/parasites in early phase (larvae have not yet matured into egg-laying adults)
Stool O&P becomes positive approximately 8 weeks after the onset of respiratory symptoms (in keeping with Ascaris life cycle)

Imaging (CXR / CT):

Migratory, transient, bilateral pulmonary infiltrates - characteristically "fleeting" (appear and resolve in different areas)
Infiltrates resolve spontaneously as larvae exit the lung

Respiratory secretions:

Larvae may be recovered from sputum or BAL fluid during the pneumonic phase
Gastric aspirate may also reveal larvae

Lung biopsy (not routinely required):

Shows striking eosinophilic infiltration of interstitial and alveolar-capillary units
Increased macrophages
No tissue necrosis or vasculitis
Larvae (Ascaris or hookworm) may be identified in specimens

Treatment and Prognosis

The condition is generally self-limited with an excellent prognosis.

Treatment	Notes
Supportive care	Adequate in most cases
Bronchodilators	For symptomatic relief of wheeze/dyspnea
Corticosteroids	Rarely needed; for severe symptomatic cases
Mebendazole	100 mg twice daily x 3 days, or single 500 mg dose (for Ascaris)
Alternatives	Pyrantel pamoate, albendazole, or ivermectin

Why treat even if symptoms resolve? Because the late GI manifestations of Ascaris (which begin ~8 weeks after respiratory onset) include malnutrition, diarrhea, abdominal pain, and intestinal obstruction. Antihelminthic treatment prevents this.

Follow-up: Since stool specimens are negative early in illness, clinical follow-up over 2-3 months is indicated with repeat stool O&P.

Position Within the Eosinophilic Pneumonia Classification

Loeffler syndrome is classified as Simple Pulmonary Eosinophilia under "Pulmonary Eosinophilic Syndromes of Known Cause," alongside:

Drug- or toxin-induced eosinophilic pneumonias
Tropical pulmonary eosinophilia (Wuchereria bancrofti/Brugia - more severe, with marked eosinophilia >3000/mm³ and bronchospasm)
Allergic bronchopulmonary mycosis (ABPA)

It contrasts with idiopathic forms (IAEP, ICEP) and systemic forms (EGPA/Churg-Strauss, hypereosinophilic syndrome) by having an identifiable parasitic cause and a benign, self-limited course.

Fishman's Pulmonary Diseases and Disorders, 2-Volume Set
Murray & Nadel's Textbook of Respiratory Medicine
Harrison's Principles of Internal Medicine, 22nd Edition (2025)

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