Our eosinophilosophy
eos counts in
EOSINOPHILIC PNEUMONIA

Eosinophilic pneumonia is considered a primary eosinophilic lung disease that is limited to the lung.1,2 The disease consists of both acute and chronic conditions in which eosinophils (EOS) infiltrate the lung. The two forms of pneumonia differ with regard to cause, onset, and course of disease.2

Acute eosinophilic pneumonia

Acute eosinophilic pneumonia is a rare eosinophilic lung disease with an estimated 9.1 cases per 100,000 patient-years. The disease tends to occur more in males than females, and patients are often in their 20s. A history of smoking is common in patients with acute eosinophilic pneumonia.2 The onset of pneumonia occurs within days and may be associated with a change in smoking habits, such as restarting smoking, increasing cigarette number, or recently starting smoking.1,2

Eosinophils icon

Role of eosinophils in acute eosinophilic pneumonia

Although the exact cause of acute eosinophilic pneumonia is unknown, eosinophil activation and recruitment to the lung is thought to occur via T helper 2 (Th2) cell– and group 2 innate lymphoid 2 (ILC2)–mediated immune responses following alveolar or airway epithelial damage from an inhaled antigen. The damage can lead to secretion of interleukin-25 (IL-25), IL-33, and thymic stromal lymphopoietin, polarizing Th2 cells and stimulating ILC2. IL-33 is thought to play an important role in this condition, and elevated levels of IL-33, IL-8, and IL-5 have been found in the blood and bronchoalveolar lavage (BAL) fluid in patients.2

EOS counts in acute eosinophilic pneumonia diagnosis

Greater than 25% of eosinophils in BAL fluid is key to establishing a diagnosis¹
Greater than 25% of eosinophils in BAL fluid is key to establishing a diagnosis¹

Modified Philit criteria used for eosinophilic pneumonia diagnosis include1,2:

  • BAL fluid eosinophils >25% and/or lung biopsy showing eosinophil infiltration of the lung parenchyma
  • Diffuse pulmonary infiltrates (bilateral)
  • Hypoxemia
  • Acute febrile illness of <1 month
  • No known cause of eosinophilic lung disease

Although these criteria are used in diagnosis, there are no formal diagnostic criteria for acute eosinophilic pneumonia2

Blood eosinophilia (>500 cells/µL) in acute eosinophilic pneumonia is rare.2

Chronic eosinophilic pneumonia

Chronic eosinophilic pneumonia is a rare eosinophilic lung disease with a reported incidence in the US of 0.5-1.2%. The disease affects females more than males, and the age range of patients tends to be from 30 to 50, although any age can be affected.2 Patients with chronic eosinophilic pneumonia often have a history of asthma and allergies. Patients typically have BAL and blood eosinophilia in addition to elevated immunoglobulin E.1,2

Clinical manifestations of chronic eosinophilic pneumonia include1,2:

  • Prolonged respiratory symptoms (respiratory failure is rare):
    • Dyspnea
    • Cough
    • Wheezing
    • Sputum
  • Mild hypoxemia or normal blood oxygen
  • Low-grade fever
  • Loss of appetite and weight loss

EOS counts in chronic eosinophilic pneumonia diagnosis

Greater than 25% of eosinophils in BAL and/or 30% of eosinophils of total white blood cells

Criteria for chronic eosinophilic pneumonia diagnosis include1,2:

  • Respiratory symptom duration >2 weeks
  • Chest radiograph showing pulmonary infiltrates
    • Infiltrates often have a peripheral predominance
  • BAL eosinophilia typically >25%
  • Blood eosinophilia (often >30% of white blood cells) and/or evidence of eosinophil infiltration of lungs
  • Exclusion of other eosinophilic lung diseases such as allergic bronchopulmonary aspergillosis or eosinophilic granulomatosis with polyangiitis (EGPA)

Could it be HES or EGPA?

Chronic eosinophilic pneumonia can have uncommon non-respiratory manifestations (arthralgias, neuropathy, skin and gastrointestinal symptoms) in addition to pulmonary infiltrates and eosinophilia. Also, patients often have a history of allergies and asthma; therefore, differentiating among chronic eosinophilic pneumonia, hypereosinophilic syndrome (HES), and EGPA in some cases may be challenging.1

Get the latest eosinophilosophy updates

References:

  1. Wechsler ME. Pulmonary eosinophilic syndromes. Immunol Allergy Clin North Am. 2007;27(3):477-492.
  2. Suzuki Y, Suda T. Eosinophilic pneumonia: a review of the previous literature, causes, diagnosis, and management. Allergol Int. 2019;68(4):413-419.