Eosinophilia

Eosinophilia is the term used to describe the presence of too many eosinophils in the circulating blood or body tissues. Typically, they make up between 1 and 5% of the blood volume.  Counts higher than 6% is considered eosinophilia. Eosinophils are one of five types of white blood cells and their primary function is to protect the body against parasite infections and also play a role in the body’s allergic response.  When called to action, these cells release toxins that attach to and kill parasitic invaders.  However, having too many eosinophils results in a higher amount of toxins and can cause damage to healthy tissues.  The amount of eosinophils is controlled by controlling the underlying cause. Some of the more rare causes of eosinophilia include: leukemia, lymphoma, hypereosinophilic syndrome (HES), and chronic eosinophilic leukemia (CEL).

Eosinophilia can be further classified as primary and secondary.  In the case of parasite infection or asthma, it is considered to be caused by these conditions and is therefore secondary eosinophilia.  However, when no cause can be found, the condition is said to be primary eosinophilia.

HES and CEL are considered to be primary forms of eosinophilia.  In HES, the patients have more than 15% blood eosinophils and evidence of end organ damage.  The large number of toxin-releasing cells cause damage to vital organs and, left untreated, could lead to heart or other organ failure, resulting in patient death.  CEL, on the other hand, follows the leukemic process in which too many eosinophils are produced by the bone marrow, thus crowding out other much needed cells.  Again, left untreated, the condition is fatal.

There have been great advances in this area of medicine in recent years with many subsets of the disorder being recognized and effective treatments being provided to patients.  The once extremely high mortality rate of HES and CEL has also been greatly affected with administration of recently approved medications.