Eosinophilia or an increase in blood eosinophil count
Eosinophils are a type of white blood cell that play a role in the immune system, particularly in fighting parasitic infections and allergic reactions. They are characterized by their granules, which contain proteins and enzymes that stain with eosin, a red dye. Eosinophils are produced in the bone marrow and circulate in the blood, but can also reside in tissues, especially the respiratory and gastrointestinal tracts.
Eosinophilia is defined as an absolute eosinophil count >500 per microliter (µL) of blood, or greater than 3% of the total white blood cell (WBC) count. Eosinophilia may be classified as mild (500-1500 cells/ µL or 3 to <10%), moderate (1500-5000 cells/ µL or 10-<20%), and severe (>5000 cells/ µL or 20% and above). Organ damage is seen in moderate and more prominently in severe eosinophilia.
The list below encompasses the known causes, but eosinophilia can be influenced by genetics, with familial eosinophilia being a known inherited condition, and genetic factors contributing to other eosinophilic disorders.
ALLERGIES
This could include medical conditions due to allergy, and allergic reactions. These include:
- Allergic rhinitis: Inflammation of the nasal passages due to allergens like house dust mite, pollen, etc.
- Asthma: Characterized by airway inflammation and constriction, leading to episodes of breathlessness and sometimes cough.
- Eczema or Atopic Dermatitis: A skin condition causing itchy, inflamed patches and rashes.
- Drug allergies: Abnormal reactions to any medication.
- Food allergies: Reactions to certain food items
PARASITIC INFECTIONS
More commonly, infection with helminths (worms), such as roundworms (ascariasis, trichinosis, toxocariasis), hookworms, tapeworms, threadworm (strongyloidiasis), and flatworms (liver fluke), leads to eosinophilia. Though not the rule, rarely protozoan parasites, like those causing amebiasis (entamoeba), can also cause elevated eosinophil counts.
CANCERS
Among cancers, certain types of leukemia, such as acute myelogenous leukemia (AML) and eosinophilic leukemia, involve the overproduction of eosinophils. Hodgkin’s and non-Hodgkin’s lymphoma can also be associated with eosinophilia. Rarely, cancers affecting the cervix, ovaries, and other sites can also cause eosinophilia.
AUTOIMMUNE AND HYPERSENSITIVITY REACTIONS
Autoimmune diseases occur as a result of immune reactions or deposition of immune complexes, caused due to an immune system dysregulation leading to loss of self-recognition of a particular ‘self cell protein’, and mounting an attack on that specific tissue/organ. The most common autoimmune condition known to be associated with eosinophilia is inflammatory bowel disease (IBD -Crohn’s disease and ulcerative colitis). Some others include primary biliary cirrhosis (PBC), bullous pemphigoid, eosinophilic granulomatosis with polyangiitis (EGPA or Churg-Strauss syndrome), eosinophilic esophagitis (EoE), eosinophilic myocarditis, and eosinophilic cellulitis/fasciitis, and some types of vasculitis.
The immune system can also cause delayed hypersensitivity reactions. DRESS syndrome, also known as Drug Reaction with Eosinophilia and Systemic Symptoms, is a severe, potentially life-threatening reaction to certain medications. It can occur from a week to 2 months after starting the particular medicine. It presents as fever, widespread red and often scaling skin rash (resembling measles with slightly raised/flat red or sometimes merging spots), and damage to organs like the liver, kidneys, lungs, and heart. Eosinophilia is a typical feature. Medications, including anticonvulsants (like phenytoin and carbamazepine), some antibiotics (like sulfonamides), and allopurinol, are strongly linked to DRESS syndrome. Sometimes, reactivation of herpesviruses is thought to play a role in triggering or exacerbating the reaction. DRESS is managed by early recognition, stopping the culprit medication, corticosteroids to control inflammation, and supportive care.
ADRENAL INSUFFICIENCY
Eosinophilia can be a sign of an endocrine problem as seen in adrenal gland insufficiency, particularly in cases of Addison’s disease. This occurs because corticosteroids, like cortisol, play a role in regulating eosinophil production and their movement out of the bloodstream. When cortisol levels are low due to adrenal insufficiency, the body’s ability to control eosinophil levels is impaired, leading to their increase.
HYPEREOSINOPHILIC SYNDROME
Hypereosinophilic syndrome (HES) is a rare group of disorders characterized by persistently high levels of eosinophils in the blood, along with evidence of organ damage or dysfunction caused by these elevated eosinophils. HES can affect various organs, including the heart, nervous system, and bone marrow. The eosinophilia is persistent, as a sustained increase typically exceeding 1.5 x 10^9/L (or 1500 cells/microliter), and both the eosinophilia and organ damage are not explained by other known conditions that can cause eosinophilia, such as those mentioned above. While some cases of HES are idiopathic (cause is unknown), others are associated with issues in the bone marrow, allergies, infections, autoimmune reactions, or cancer.
Symptoms can vary depending on the organs affected and may include:
- Skin rashes, itching, and swelling.
- Fatigue, fever, and weight loss.
- Respiratory problems like cough and shortness of breath.
- Gastrointestinal issues like abdominal pain, nausea, and vomiting.
- Neurological symptoms such as dizziness, memory loss, or confusion.
- Cardiovascular problems, like heart failure or blood clots.
It is diagnosed with blood tests, bone marrow biopsy, and exclusion of other causes. It is treated with corticosteroids to reduce inflammation and eosinophil levels, chemotherapy and targeted therapy, and stem cell transplant in very severe, unresponsive cases. Without treatment, HES can be fatal due to organ damage, particularly heart failure. Early diagnosis and treatment are crucial for improving outcomes.
Also read:
Autoimmune Diseases: 15 Well-Known Types and Medical Management