What is eosinophilia

It is essential to clarify the causes!

Two years ago, the family doctor found a significantly increased number of eosinophils in the differential blood count of a 43-year-old patient - almost as an incidental finding. The medical history and initial tests did not reveal any evidence of an allergy or infection as a trigger for the persistent, asymptomatic eosinophilia. How should the family doctor proceed?

Due to the symptom-free course, it is easy to wait for PD Dr. med. Ulrich Mey from the Kantonsspital Graubünden, Chur [1], not a viable option: In order to avoid damage to tissues and end organs, a patient in whom the number of eosinophils is permanently increased must be treated. Organ dysfunctions such as dyspnea, heart failure, pleural effusions or neurological symptoms, among other things, can arise from eosinophilic infiltrates regardless of the trigger for eosinophilia.

Atopy, medication, parasites?

In terms of differential diagnosis, the first thing to do is to investigate the possible causes of what is known as secondary eosinophilia, emphasizes Mey (see overview). This form arises in response to allergens or parasites and is amenable to specific treatment. Globally, parasitoses are the most common triggers of eosinophilia, but in our part of the world it is often caused by atopy, autoimmune diseases and medication. Endocrine causes (e.g. Addison's disease) and neoplasms (malignant lymphomas, solid tumors) can also be considered (table).

A careful anamnesis with questions about allergies, travel and medication taken usually provides quick information on possible causes. Depending on the patient's information and the findings of the physical examination, the attending physician determines which stool and laboratory tests are necessary and which spectrum of parasitic pathogens can be used. Since an HIV infection can also trigger eosinophilia, an AIDS test should always be carried out, warns Mey.

Medical history and stool tests normal

In the case of the 43-year-old, however, there was neither an atopic predisposition, nor did the long-standing heavy smoker (exposure of approx. 35 pack years) suffer from asthma. He had also not taken medication regularly, nor had any allergies or rheumatic diseases occurred. There was also no evidence of allergies or asthma in the family history. The family doctor ruled out an immunological-rheumatic genesis as well as a drug-associated eosinophilia. The patient, a native of Bosnian who left his home country around 19 years ago, also stated that he had never been to the tropics. Multiple stool examinations for parasitic pathogens remained inconspicuous.

Further diagnostics with imaging procedures and serology

During the physical examination, the doctor recently found only slightly prominent cervical lymph nodes. Abdominal ultrasonography, echocardiography, lung function tests and a chest x-ray showed no abnormalities. The most recent laboratory diagnostics confirmed a mild leukocytosis (12.9 g / l) with a significantly increased eosinophil content (31.5%, normal: 2.0-4.0%). This corresponds to an absolute eosinophil count of 4,063 / µl (norm <600 µl). The plasma IgE level was significantly increased to 1,081 kU / L (norm <166 kU / L). The AIDS test remained negative.

Continuing to search for infections Despite the stool examinations already carried out, the exclusion of an infectious, especially parasitic disease by means of serology remains the top priority, emphasizes Mey, whom the family doctor finally called in as an expert. Important pathogens are worms (helminths), especially Strongyloides stercoralis (dwarf threadworms), hookworms and Toxocara canis (dog roundworm). Their incidence in our part of the world is underestimated.

Exploit Parasite Serology!

Since the severity of eosinophilia, e.g. in strongyloidiasis, can vary widely and larvae are hardly or intermittently excreted in the stool, the diagnosis can only be made through serological tests, says Mey. Agar plate cultivation remains the most widely used and recommended technique. Sensitivity and specificity of the antibody-based detection method ELISA (enzyme-linked immunosorbent assay) reach almost 100% when specific antigens are presented, reports Mey.

In the present case, the serological diagnosis was negative for Trichinella, Toxocara canis, Echinococcus multilocularis, Cysticercosis, Gnathostoma and Echinococcus granulosus. There was still a positive serology for Strongyloides stercoralis.

"Souvenir" from the home country

The diagnosis was therefore strongyloidiasis, even if specific stool examinations for larvae were again negative. The patient was most likely infected at a young age in Bosnia, Mey suspects. The infection could persist for decades without significant clinical impairment. The literature gives the prevalence of strongyloidiasis in Bosnia at up to 7.3%.

In case of parasitosis, be careful with steroids

The 43-year-old received anti-parasitic therapy with ivermectin (200 µg / kg body weight) for two days. The haematological follow-up after two weeks showed a clear decrease in the absolute number of eosinophils. Three months later she had normalized.

Mey explains why it is so important to search carefully for the cause of the eosinophilia and not to treat the excessive immune response immediately: If the family doctor had ruled out secondary eosinophilia prematurely, the persistent eosinophilia would have been given - since there was no hematological neoplasia either idiopathic hypereosinophilic syndrome (HES) was suspected with an absolute cell count in the peripheral blood>? 1? 500 / µl. In strongyloidiasis, steroids, in this case the therapy of choice, can lead to life-threatening hyperinfection syndromes after just one to two weeks of immunosuppression.

Stefanie Lindl-Fischer

1) Practice 2012; 101 (7): 483-487