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Improving the understanding of different types of Hypereosinophilic Syndrome

Published: April 21, 2022

Hypereosinophilic syndrome (HES) is a group of rare blood disorders. It occurs when the body produces high numbers of white blood cells called eosinophils that eventually cause organ damage. Eosinophils play a key role in the body’s defense against infection. Patients are diagnosed with HES when they have over three times more eosinophils (>1500 eosinophils per microliter) in their blood than expected for a long period of time (more than one month) and symptoms of organ involvement. Over time, these high levels of eosinophils cause long-term damage to various organs in the body. The most commonly affected organs include the skin, lungs, and heart. There are several types of HES. These are idiopathic HES (I-HES), where there is no known cause; myeloproliferative HES (M-HES), lymphocytic HES (L-HES) and Chronic Eosinophilic Leukemia, Not Otherwise Specified (CEL-NOS), which all have different causes. One of the challenges faced by doctors is distinguishing between the different types of HES. Understanding the differences and similarities between them will help doctors improve diagnosis and treatment. This should improve the lives and treatment options for patients living with HES.

A recent review article on HES by Requena and colleagues was published in The Journal of Allergy and Clinical Immunology: In Practice. This review aimed to improve understanding of the different types of HES. The authors examined the description of patients diagnosed with HES in numerous studies published over 20 years. They focused on the patients’ age and sex, the signs and symptoms of the different types of HES at diagnosis, organ damage over time and the treatment given to patients. Data was obtained from 188 scientific papers. These papers fully described 347 individual cases of HES.

The average age of patients with HES was 44 years old at diagnosis. Patients with M-HES tended to be younger than those with other types of HES. The prevalence of all types of HES was greater in males, particularly among those with M-HES or CEL-NOS. At the time of diagnosis, the number of eosinophils in the blood was highest for CEL-NOS and lowest for L-HES. Heart symptoms were common for all HES variants. Specific organ involvement was seen between HES subtypes. The most notable differences between them were reported as follows: patients with M-HES and CEL-NOS presented more commonly with enlarged spleens compared to those with other varieties of HES; patients with L-HES had more reported skin abnormalities; and patients with I-HES seemed to have abnormalities in the lungs, heart and bone marrow more consistently. The most common treatment for I-HES, L-HES and CEL-NOS were corticosteroids, and for M-HES a chemotherapy drug called imatinib.

Overall, this review revealed some similarities and differences between the different types of HES. It also showed that looking at individual patients can provide extra insights in rare diseases like HES, where analyzing large groups of patients can be difficult. Future studies should use more consistent definitions for the different types of HES. There is also a need for more consistent methods for assessing signs and symptoms of HES and for assessing how well patients respond to treatment. This may allow doctors and scientists to develop new treatments for HES and improve patients’ lives.

The Journal of Allergy and Clinical Immunology: In Practice is an official journal of the AAAAI, focusing on practical information for the practicing clinician.

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