Eosinophilia: A Brief Discussion Regarding Causes and Management

What Does Eosinophilia Mean?

Eosinophils are a type of white blood cell found in the body. They have granules in their cytoplasm that contain proteins and bind with certain dyes like ‘eosin.’ These cells originate from the bone marrow and are produced in response to certain signals from the body, such as IL-5 (interleukin 5), IL-3 (interleukin 3), and GM-CSF. They have a short lifespan in the bloodstream, lasting around 4.5 to 8 hours, but can stay in tissues, mainly in the respiratory and gastrointestinal tracts, for 8 to 12 days. Eosinophils comprise less than 5 percent of the white blood cell count.

Eosinophilia refers to an increase in the number of circulating eosinophils. Eosinophilia is said to be present when the absolute eosinophil count is more than 500/mm^3 (500 per cubic millimeter of blood). Depending on the count, eosinophilia can be classified as mild (500 to 1500/mm^3), moderate (1500 to 5000/mm^3), or severe (>5000/mm^3). Hypereosinophilic syndrome is diagnosed when there is a persistent increase in eosinophil count above 1500/mm^3 on two separate occasions at least one month apart or significant tissue eosinophilia.

What Is the Pathophysiology of Eosinophils?

Eosinophils undergo differentiation in the bone marrow, ceasing further maturation upon leaving. Primarily located outside the bloodstream, they inhabit tissues. In eosinophil-related disorders, these cells are recruited into affected tissues. Immune responses mediated by T helper-2 cells, along with IL-5 production, drive eosinophilopoiesis and activation. IL-5 is the primary cytokine responsible for eosinophil production and activation. Upon activation, eosinophils degranulate, releasing cationic proteins into tissues to carry out their functions. These proteins, including proteolytic enzymes, may cause damage to the host wall. Additionally, eosinophils release cytokines such as IL-10 (interleukin 10) and IL-14 (interleukin 14), contributing to maintaining homeostasis and immunoregulation.

How Common Is Eosinophila?

The exact occurrence and frequency of eosinophilia need to be better understood. Eosinophilia does not show a preference for a specific gender. However, its prevalence can vary depending on geographical factors and underlying causes. Parasitic infections are more common in tropical regions, while allergic conditions are widespread in developed countries. Idiopathic hypereosinophilia is typically diagnosed between the ages of 20 and 50, but cases at very young or old ages are also observed.

What Are the Causes of Eosinophilia?

The causes of eosinophilia are mentioned below:

1. Allergic disorders -

This is the first cause that has to be ruled out.

• In asthma, bronchoconstriction occurs due to allergens like dust, pollen, mites, cold, etc. So, the patient is seen to have a dyspnea problem as well.

• Hay fever is a form of allergic rhinitis.

• Drug allergy (Sulphonamides, Allopurinol, antiepileptic drugs, etc).

• Food hypersensitivity.

2. Parasitic infestations -

Following parasites can lead to high eosinophils.

• Ascariasis.

• Ancylostoma duodenale.

• Enterobiasis.

• Taenia solium.

• Filariasis.

• Hydatid cyst.

3. Skin disease:

• Eczema.

• Scabies.

• Pemphigus.

• Psoriasis.

• Contact dermatitis.

4. Pulmonary eosinophilia.

5. Miscellaneous:

• Hodgkin's lymphoma.

• ALL (acute lymphoblastic leukemia).

• CML (chronic myeloid leukemia).

• Eosinophilic gastritis.

• Esophagitis.

• HIV (human immunodeficiency virus) infection.

What Are the Potential Consequences of High Eosinophil Counts?

At times, elevated eosinophil levels can lead to inflammation in specific body parts, termed as an eosinophilic disorder or hypereosinophilia syndrome (HES). These disorders are named based on the affected areas and include:

1. Eosinophilic cystitis (a disorder affecting the bladder).

2. Eosinophilic pneumonia (a disorder affecting the lungs).

3. Eosinophilic Fasciitis: A condition impacting the fascia, the connective tissue running throughout the body.

4. Eosinophilic Gastrointestinal Disorders (EGID): This category encompasses eosinophilic esophagitis affecting the esophagus, along with conditions impacting the colon, stomach, and small intestine.

5. Eosinophilic Granulomatosis with Polyangiitis (EGPA): Churg-Strauss syndrome; this condition affects various organs, including the lungs, heart, sinuses, and others.

6. Hypereosinophilic Syndrome: A rare set of conditions linked to consistently high levels of eosinophils. This syndrome commonly affects the heart, central nervous system, skin, and respiratory tract.

How Is Eosinophilia Diagnosed?

Eosinophilia is diagnosed with a CBC (complete blood count) with a differential count.

After eosinophilia is confirmed, the underlying cause should be searched for.

To rule out underlying causes, a medical history is taken, and then accordingly, investigations are done, such as:

• Chest X-ray and spirometry for asthma.

• Liver and kidney profile tests.

• Stool analysis and serological testing for parasitic infestation.

• Allergy testing to find causative allergens.

• Peripheral smear examinations and bone marrow studies are needed to rule out a myeloproliferative neoplasm.

• ELISA (enzyme-linked immunosorbent assay) tests for HIV (human immunodeficiency virus).

So, various tests are done according to need.

What Is the Treatment for Eosinophilia?

• Corticosteroids, Montelukast, or strong anti-inflammatory drugs can be prescribed for allergy disorders.

• A bronchodilator inhaler or nebulization can also be prescribed as needed for asthma.

• For parasites, Albendazole 400 mg is a good drug.

• For skin problems, treatment is done according to the cause. For example, topical Betamethasone.

• Treatment can be straightforward for certain conditions, such as drug and food allergies, or infections, such as discontinuing the harmful substance or using antibiotics.

• In cases where steroids do not work for hypereosinophilic syndrome and chronic eosinophilic leukemia, medications like hydroxyurea and interferon-alpha are effective.

• In severe cases, additional treatments like cytotoxic agents and stem cell transplants have provided some benefits.

When to Seek Medical Care?

Doctors will find eosinophilia while running blood tests to diagnose symptoms one already has. So, it may not be unexpected. But sometimes, eosinophilia can be found by chance. Discuss with doctors about the results. Evidence of eosinophilia and other test results can help identify the underlying cause of an individual's illness. The doctor may suggest other tests to check an individual's condition.

It is important to know what other health conditions one may have. This condition will likely resolve with the proper diagnosis and treatment. If they have hypereosinophilic syndrome, doctors may prescribe medicines such as corticosteroids. Because this condition can cause major concerns over time, they will check in regularly.

Conclusion:

Do not neglect high eosinophils in CBC (complete blood count). Rule out the underlying cause, and treatment is done accordingly. The leading cause of elevated eosinophil levels is allergies. Managing the body's allergic responses through treatment can help prevent eosinophilia associated with allergies. However, there are instances when eosinophilia may indicate an underlying condition beyond one's control.