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Eosinophilia is a disorder that may arise from a number of etiologies. Thus the first task in treatment is to find out whether the condition is primary or secondary. Secondary eosinophilia is due to parasitic infection or drug hypersensitivity in the majority of cases.
The first step is to withdraw all medications that are not essential for the patient’s continued health. This is so because there is a wide range of drugs that are capable of causing hypersensitivity reactions, even months or years after starting treatment. Even if a drug is indicated for the patient, it should be continued only as long as there is no sign of organ involvement, such as pulmonary or renal inflammation.
The appearance of fever, rashes, or arthralgia or other systemic symptoms warrant the cessation of the suspected drug.
Another step is stool and serologic testing for parasitic infestation. Three consecutive stool specimens should be tested for parasite ova, beside specific blood tests, depending on the patient’s history of travel and the place of residence, past and present.
If the patient has any chance of having Strongyloides stercoralis infection, it is mandatory to do serologic testing for this parasite, which does not show up in microscopic examination of stool specimens. This is because Strongyloidiasis has the tendency to flare up and disseminate throughout the body when glucocorticoid treatment is initiated.
In case this condition is suspected, but not confirmed, and if immediate initiation of treatment is necessary, ivermectin should be given together with the steroid. In other conditions, once the diagnosis of parasitic infestation is established, adequate and effective anti-parasitic treatment should be given.
If none of these underlying disorders are found, or if the eosinophil count remains high despite treatment, other possibilities should be taken into account. Tests such as antibody testing for vasculitides and other connective tissue disorders, imaging of the thorax and abdomen, and bone marrow aspiration for biopsy may be indicated among others. However, many of these tests are concerned as much with picking up eosinophilia-related organ complications as with establishing the etiology.
For instance, cardiac involvement may be signaled by high cardiac troponin, EKG variations or cardiac dysfunction on echocardiography. Other serious complications include hypoxia due to lung infiltration and neurologic deficits. In case any of these are found to be present, high doses of corticosteroids are immediately started, with the above proviso that ivermectin is to be added simultaneously in case strongyloidiasis is conceivably present. Only if the patient does not respond to corticosteroids is specialist therapy with imatinibmesylate or vincristine warranted.
Other emergent situations which require immediate corticosteroid therapy include:
HES types need to be differentiated. The F/P type is treated first of all with imatinib in order to achieve remission. Corticosteroids do not usually effect a reduction in eosinophils in this type, but are added on in case of cardiac involvement, in order to prevent the onset of acute myocarditis. The L-HES subtype is treated with corticosteroids, in contrast, while T-cell inhibitors such as interferon-α are added in refractory cases or if the dosage of corticosteroids is to be reduced. Such patients also require careful follow-up to detect T-cell lymphoma.
Most other cases of HES respond to corticosteroids if indicated to reduce the eosinophil count. This depends on whether complications have set in, and if so, which organ is affected and to what extent. The dose varies widely from patient to patient. If corticosteroids are to be taken in a high dose, or if the adverse effects are severe, agents like hydroxyurea and interferon-α are effective.
Patients with myeloproliferative disease are often treated with imatinibmesylate. All these drugs are also used in patients who do not respond to steroid therapy. Mepolizumab is a more recent addition, which antagonizes the action of interleukin-5, an important chemokine in the production of eosinophils.