What Is Eosinophilic Pneumonia?

Eosinophilic pneumonia (EP) is a rare disorder characterized by a rapid increase of eosinophils—a type of white blood cell that is usually produced in response to allergens, inflammation, or parasitic infections—in the lungs and bloodstream.

Many conditions including certain disorders, drugs, chemicals, fungi, and parasites may cause eosinophils to accumulate in the lungs.

EP can cause a range of symptoms, from fever and shortness of breath to muscle aches and weight loss. 

This article discusses the symptoms, causes, diagnosis, and treatment for eosinophilic pneumonia.

Symptoms

Symptoms of eosinophilic pneumonia vary widely, from mild to life-threatening, depending on the type of EP you have and whether it is acute or chronic.

Acute eosinophilic pneumonia usually progresses quickly, causing:

• Fever
• Shortness of breath
• Chest pain worsened by deep breathing
• Cough
• Fatigue or malaise
• Muscle aches

If left untreated, your oxygen levels can plummet progressing to acute respiratory failure in a few hours or days.

Chronic eosinophilic pneumonia, on the other hand, progresses much more slowly, over days or weeks. If left untreated, it may also have severe consequences, although it is more likely to remit on its own.

Causes

Eosinophilic pneumonia may be idiopathic, that is it may come on for unknown reasons.

That said, it may be triggered by other causes such as:

• Smoking and other inhalation exposures
• Certain medications
• Infections

Some occupational factors, like exposure to inhaled dust, have been shown to trigger eosinophilic pneumonia. Certain drugs like minocycline, daptomycin, and venlafaxine, an antidepressant, have also been linked to eosinophilic pneumonia.

Infectious causes of eosinophilic pneumonia are usually caused by allergens and parasites, including:

• Ascaris infections
• Hookworm. EP may occur after infection with Ancylostoma duodenale or Necator americanus as larvae migrate through the lungs.
• Strongyloides stercoralis infection by filariform larvae
• Paragonimus. Also known as the lung fluke, Paragonimus infections are generally acquired after ingesting raw or undercooked seafood, particularly crabs and crayfish.
• Wuchereria bancrofti, Brugia malayi, and Brugia timori nematode infection. Tropical filarial pulmonary eosinophilia (TFPE) occurs in individuals from tropical regions who acquire nematode infections from being infected by mosquitos during a blood meal. 
• Dog ascarid, Toxocara canis, or the cat ascarid, Toxocara cati can cause visceral larva migrans, a type of eosinophilic pneumonia

Noninfectious causes of eosinophilic pneumonia include:

• Allergic reactions, such as allergic bronchopulmonary aspergillosis and sensitization to other non-Aspergillus fungi
• Drug exposures (e.g., nitrofurantoin, non-steroidal anti-inflammatories)
• Toxin exposure (e.g., particulate metals, inhalational drugs of abuse)
• Churg-Strauss syndrome
• Hypereosinophilic syndrome
  

Diagnosis

The first step in diagnosing any lung infection is to take a thorough patient history, asking one to describe their symptoms in detail, and perform a focused physical exam.

If EP is suspected—which is more likely the case if there is a history of parasitic infection or exposure to certain drugs—then more specialized tests may be ordered by your healthcare provider.

Bronchoalveolar lavage (BAL) is the key test used to diagnose EP. This test removes fluids from the lower part of the respiratory tract to quantify the degree of eosinophilia, look for infection, hemorrhage or malignancy, with the goal of determining the cause or ruling out the presence of disease.

During the BAL procedure, a narrow, flexible tube (called a bronchoscope) is slid down the windpipe into the lungs and a sterile solution is squirted into the area of question, washing out cells in the process. Aspiration—or the collection of fluid by this method—allows scientists to study the cells in great detail.

Eosinophils usually make up between 0 to 6% of the white blood cells, so levels beyond that may raise one’s suspicion of EP. In fact, eosinophil levels during acute infection can skyrocket, and the presence of 25% or more eosinophils is an indication of EP.

In addition to BAL, chest C-rays and CT scans may also be ordered. They may show consolidations that may be indicative of EP, although these findings are non-specific and often serve as only one piece of the puzzle.

Treatment

Treating the underlying cause of EP is integral to lessening the progression of your symptoms and avoiding serious medical complications.

If you have acute EP, high-dose steroids are usually initiated immediately, due to the possibility of rapid progression to acute respiratory distress syndrome (ARDS).

In cases of chronic EP, oral prednisone, a steroid, may be prescribed by your healthcare provider.

Significant improvement is often seen within one to two weeks but can occur as quickly as 48 hours. In rare cases, people may need to take steroids long-term.

Diffidently, symptoms may go away on their own in mild cases of acute or chronic cases, but you should seek immediate medical attention to avoid serious medical complications.

Prognosis

When EP is promptly recognized and treated, the prognosis is generally excellent. Complete resolution of your symptoms, including infiltrates on imaging, usually occurs within one month after treatment is initiated.

Summary

EP is an uncommon lung infection, characterized by a massive influx of eosinophils, that may be caused by smoking, environmental exposures, certain medications, and infections. 

A Word From Verywell

Eosinophilic pneumonia is very uncommon and mimics other types of pneumonias and the flu. Cessation of the offending agent, taking antibacterials or antifungals if needed, and prompt treatment with high dose corticosteroids usually results in near-complete resolution of your symptoms and stops the progression of your EP to ARDS.