Mondo Description A disorder characterized by episodes of swelling under the skin (angioedema) and an elevated number of the white blood cells known as eosinophils (eosinophilia). During these episodes, symptoms of hives (urticaria), fever, swelling, weight gain and eosinophilia may occur. Symptoms usually appear every 3-4 weeks and resolve on their own within several days. Other cells may be elevated during the episodes, such as neutrophils and lymphocytes. Although the syndrome is often considered a subtype of the idiopathic hypereosinophilic syndromes, it does not typically have organ involvement or lead to other health concerns.