Hypereosinophilic syndrome is a rare idiopathic disorder of dogs characterized by eosinophilia > 5 x 109/L and marked increased in circulating immunoglobulin E in the absence of paraneoplastic lymphoma or other underlying disease.
This syndrome is characterized by a variable eosinophilia as well as a massive infiltration of several organs by mature eosinophils, leading to organ dysfunctions and sometimes resulting in death.
Clinically affected dogs often present with episodic vomiting, diarrhoea, abdominal discomfort and coughing. These symptoms are often referable to underlying eosinophilic enteritis and eosinophilic bronchopneumopathy.
Blood tests confirm a marked hypereosinophilia, with bone marrow aspiration biopsies revealing hyperplasia of the eosinophilic cell line with no evidence of abnormal blast activity. Bronchoalveolar lavage usually shows increased numbers of eosinophils in the wash fluid and biopsies of various organs usually shows eosinophilic infiltrates in many organs.
Cytogenetic analysis and measurement of serum IgE concentrations are used to differentiate hypereosinophilic syndrome from eosinophilic leukemia.
Exclusions of other causes of eosinophilia such as parasites, hypoadrenocorticism, leukemia, fungal infections, eosinophilic enteritis, eosinophilic cellulitis, eosinophilic bronchopneumopathy and mast cell tumors are important before establishing a diagnosis.
Some cases eventually resolve spontaneously.
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