Hypereosinophilic syndrome is a group of rare blood disorders characterized by increased levels of eosinophils (a type of white blood cell that plays a role in the human immune system) persisting for more than six months. The signs and symptoms are due to involvement of several internal organs and there is usually no evidence of parasites, allergy, or other known causes of an elevated eosinophil count. This condition largely occurs in males, typically at middle age. It usually presents with fever, weight loss, fatigue, and rash. An enlarged liver and spleen and liver is often present. The lungs, kidneys, heart, and nervous system can also be affected.
The hypereosinophilic syndrome is a disease characterized by a persistently elevated eosinophil count in the blood for at least six months without any recognizable cause, with involvement of either the heart, nervous system, or bone marrow.
HES is a diagnosis of exclusion, after clonal eosinophilia and reactive eosinophilia have been ruled out.