Loefflers syndrome pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Soroush Seifirad, M.D.[2]

Overview

It is understood that Löffler syndrome is the result of transpulmonary passage of helminth larvae. Helminths, with a pulmonary life cycle are responsible for this syndrome, among them are Ascaris lumbricoides, Ascaris suum, Ancylostoma duodenale, Necator americanus, and Strongyloides stercoralis.

Pathophysiology

Pathogenesis

• It is understood that Löffler syndrome is the result of the transpulmonary passage of helminth larvae. Helminths, with a pulmonary life cycle are responsible for this acute hypersensitivity reaction syndrome, among them are Ascaris lumbricoides, Ascaris suum, Ancylostoma duodenale, Necator americanus, and Strongyloides stercoralis.
• Pathogen is usually transmitted via the oral route (Ascaris) or penetrate the skin (Necator) to the human host.
• Following transmission/ingestion, infecting larvae reach the lungs via the bloodstream, penetrate into alveoli, mature, and ascend the airways before descending the alimentary tract into the small bowel
• Ascaris is the most common cause of Löffler syndrome worldwide. On the other hand, migrating larvae of hookworms (Ancylostoma duodenale, Necator americanus) and Strongyloides are less likely to elicit symptoms or pulmonary eosinophilia.

(1) Adult worms live in the lumen of the small intestine. A female may produce approximately 200,000 eggs per day, which are passed with the feces. (2) Unfertilized eggs may be ingested but are not infective. (2) and (3) Fertile eggs embryonate and become infective in 5-10 days depending on the environmental conditions (optimum: moist, warm, shaded soil). (4) Infective eggs are swallowed. (5) The larvae hatch, invade the intestinal mucosa and are carried via the portal, then systemic circulation to the lungs. (6) The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat. (7) The larvae are then swallowed. Upon reaching the small intestine, they develop into adult worms. The female Ascaris begin depositing eggs in 8-10 weeks. Adult worms can live 1 to 2 years. - Source: https://www.cdc.gov/

The life cycle of hookworms, (Ancylostoma duodenale and Necator americanus). Eggs are passed in the stool The number 1, and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil The number 2, and after 5 to 10 days (and two molts) they become filariform (third-stage) larvae that are infective The number 3. These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed The number 4. The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host The number 5. Most adult worms are eliminated in 1 to 2 years, but the longevity may reach several years. Source:https://www.cdc.gov/parasites/hookworm/biology.html.Life cycle image and information courtesy of DPDx.

• Pulmonary eosinophilia is a different term, with a wider range of infectious and noninfectious pathophysiology.
• Parasites without pulmonary cycle has been linked to pulmonary eosinophilia.
• It is believed that pulmonary eosinophilia is a hypersensitivity reaction due to circulating, but not local inflammatory mediators such as likeinterleukin-5 (IL-5).
• Since challenged athymic mice have not developed pulmonary eosinophilia, it has been suggested that pulmonary eosinophilia is aT cell-dependent phenomenon.

Associated Conditions

Conditions associated with Loeffler syndrome include subjects infected with:

• Ascaris lumbricoides,
• Ascaris suum, Ancylostoma duodenale,
• Necator americanus,
• Strongyloides stercoralis.

Gross Pathology

• Loeffler syndrome has its own characteristic imaging findings.
• Biopsy is rarely performed
• Diagnosis is based on clinical findings, radiographic findings, and shreds of evidence of parasite presence in pulmonary secretions.
• Blood-tinged sputum might be presented.

Microscopic Pathology

• Eosinophils may be present in sputum
• Eosinophil-derived Charcot-Leyden crystals may be present in blood-tinged sputum
• Stool examinations are generally negative at the time of pulmonary symptoms and thus not useful in the diagnosis of Löffler syndrome.
• Ascaris, Strongyloides, or hookworm larvae might be detected in the respiratory secretions

Charcot–Leyden crystals and eosinophil granulocytes in allergic sinusitis.By Patho - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=24411266

Eosinophils in peripheral blood in a patient with eosinophilia of unknown etiology. By Ed Uthman, MD, Houston, Texas, USA - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=10813548

• Since biopsy is not indicated in patients with the lofeffler syndrome, reported pathological presentations of Loeffler syndrome are based on the autopsy of patients who passed away from another cause while they concomitantly had simple pulmonary eosinophilia.
• It has been shown that eosinophilic infiltration occurs in the bronchi and bronchioles and in the alveolar and interstitial spaces.
• Usually no parasitic form has been found in the lungs.