Blood eosinophilia is defined by too high a level of eosinophils in the circulation. These blood cells, produced by the bone marrow and present in all individuals at a rate of between 300 and 600 per mm3 of blood, belong to the family of white blood cells. Eosinophilia syndrome is defined when the level of eosinophils exceeds this threshold. Eosinophilia is mainly secondary, linked to another pathology. When sustained, it can cause damage at different levels: skin, respiratory, digestive, heart, etc.

Definition of eosinophilia

Blood eosinophilia is defined by too high a level of eosinophils in the circulation. These blood cells, produced by the bone marrow and present in all individuals at a rate of between 300 and 600 per mm3 of blood, belong to the family of leukocytes (or white blood cells). Eosinophilia syndrome is defined when the level of eosinophils exceeds this threshold.

Eosinophilia can be:

• Mild: the level of eosinophils is between 600 and 1 per mm500 of blood;
• Moderate: the level of eosinophils is between 1 and 500 per mm5 of blood. This is called hypereosinophilia;
• Severe: the level of eosinophils is greater than 5 per mm000 of blood.

The majority of eosinophils are found in the tissues, at the mucosal interfaces with the environment, especially at the pulmonary and gastrointestinal levels. They play an important role in the immune response – especially parasitic – and in hypersensitivity reactions.

Types of eosinophilia

Three types of eosinophilia can be distinguished:

• Primary: in less than 5% of cases, it is genetic, linked to a defect on chromosome 5 and transmitted in an autosomal dominant fashion. It presents with or without symptoms;
• Secondary or reactive: in more than 95% of cases, it is secondary to an acquired pathology;
• To this classification is added idiopathic hypereosinophilia, that is to say without an identifiable cause, defined by a level of eosinophils greater than 1 per mm500 of blood for at least six months and to which is added the impairment of an organ.

Causes of eosinophilia

The causes of secondary eosinophilia are varied:

• Respiratory and food allergies and dermatitis represent up to 80% of cases of eosinophilia in industrialized countries: allergic rhinitis (mild eosinophilia), asthma, eczema…;
• Infestations and infections: parasitosis and helminths (worms);
• Drug hypersensitivity;
• Eosinophilic pulmonary syndrome;
• Idiopathic hypereosinophilic syndromes (severe eosinophilia);
• Certain systemic inflammatory diseases: Churg-Strauss syndrome (characterized by inflammatory destruction of blood vessels), sarcoidosis, rheumatoid arthritis, Sjögren syndrome (autoimmune disease of the exocrine glands), scleroderma (autoimmune disease characterized by hardening of the skin), other systemic inflammatory vessel damage, lupus erythematosus and inflammatory myopathies;
• Inflammatory bowel disease;
• Neoplasms (2 to 7% of cases): lympho or myeloproliferative diseases (abnormal production of certain cells in the bone marrow), Hodgkin’s disease (form of cancer of the lymphatic system).

Diagnosis of eosinophilia

Eosinophilia must first be confirmed by measuring the level of absolute eosinophils using a complete blood count, or blood count (CBC).

When confirmed, questioning the patient is a key step in the process of diagnosing the cause of eosinophilia, secondary or primary. He must be interested in:

• Personal and family history, in particular genetic predisposition to the development of common allergies, cancer…;
• Recent or ongoing treatments;
• Lifestyle: personal or professional exposure to allergens, toxins, animals, etc.;
• To the ethno-geographic context and to stays in parasitic endemic areas.

A physical examination completes this questioning: dermatological, respiratory, digestive manifestations, etc.

The clinical examinations then consist of:

• Rule out organ dysfunction: complete liver tests, plasma creatine, urine sediment, troponin (protein complex that sensitizes muscle cells to calcium);
• Look for an inflammatory syndrome: sedimentation rate and / or C reactive protein (CRP);
• Look for possible parasites;
• Take a chest x-ray (if you have respiratory symptoms).

Depending on the results of previous analyzes, additional examinations may be necessary:

• Search for parasites in stool, urine, bronchoalveolar lavage (BAL), sputum…;
• Tissue biopsy;
• Scanner or Magnetic Resonance Imaging (MRI);
• Bone marrow biopsy;
• And many more

People affected by eosinophilia

The incidence of eosinophilia is estimated between 1 and 1,5% for the general population.

Factors promoting eosinophilia

To the causes triggering secondary eosinophilia, the following factors can be added:

• Cholesterol emboli disease (a particular form of arterial embolism);
• Radiotherapy;
• The reaction of a graft during transplantation;
• Occupational pneumopathies.

Skin manifestations

When the skin is affected, pruritus (itching related to skin conditions), skin rashes, subcutaneous edema, hives, mucous erosions… can occur.

Respiratory manifestations

When the lungs are involved, the breathing is wheezy and the patient suffers from shortness of breath. The main symptoms are asthma, cough, rhinitis and / or sinusitis, pulmonary infiltrates (opacities), pleural effusion, etc.

Digestive manifestations

Abdominal pain, vomiting or diarrhea can occur when the digestive system is affected.

Cardiac events

When the heart is affected, symptoms of heart failure, valve disease (dysfunction of heart valves), cardiomyopathy (dysfunction of the heart muscle), pericardial effusion, or myocarditis (inflammatory disease of the heart) are shortness of breath and fatigue. .

Other symptoms

• Rheumatological manifestations (arthralgia, myalgia, arthritis…);
• Neurological manifestations (paresthesias, visual disturbances, ischemic stroke, etc.);
• Weightloss ;
• Fever ;
• Night sweats ;
• Tired ;
• Cough ;
• Deep or superficial venous thrombosis, anemia, arterial embolism…;
• Chest pain ;
• Stomach pain;
• Urogenital manifestations;
• Confusion ;
• Coma (if idiopathic hypereosinophilia syndrome).

Apart from primary and idiopathic eosinophilia, treatment for eosinophilia will depend on the cause.

The treatment of hypereosinophilia syndrome linked to chronic leukemia lies, before any chemotherapy or allogeneic bone marrow transplant, in the prescription of drugs that block the expansion of eosinophils. In other situations of lymphoid and idiopathic hypereosinophilia syndromes, the treatment of choice remains corticosteroids.

It should be noted that therapeutic abstention is the rule in the many situations of hypereosinophilia without any organic manifestation.

There is no way to prevent the onset of eosinophilia. On the other hand, detecting it as quickly as possible, that is, before the appearance of organ dysfunctions, is crucial. Any eosinophilia should therefore alert the doctor or patient and be investigated for its cause.