A heterogeneous group of disorders with the common feature of prolonged eosinophilia of unknown cause and associated organ system dysfunction, including the heart, central nervous system, kidneys, lungs, gastrointestinal tract, and skin. There is a massive increase in the number of eosinophils in the blood, mimicking leukemia, and extensive eosinophilic infiltration of the various organs. It is often referred to as idiopathic.