Epidemiology
HES is very rare, with only 50 cases being noted and followed up in the United States between 1971 and 1982, corresponding roughly to a prevalence of 1 to 2 per million people. The disease is even more uncommon within the paediatric population.
Patients who lack chronic heart failure and those who respond well to Prednisone or a similar drug have a good prognosis. However, the mortality rate rises in patients with anaemia, chromosomal abnormalities or a very high white blood cell count.
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