Diagnosis and medical management of canine idiopathic hypereosinophilic syndrome presenting as a solitary intestinal mass in a dog

Summary A 5‐year‐old, female, neutered Border Collie cross dog presented with progressive borborygmus, vomiting and weight loss. Initial investigation revealed marked peripheral eosinophilia (7.62 × 10 9 /L, reference interval: 0.06–1.23), a large solitary jejunal mass, a single hepatic nodule and multiple markedly enlarged abdominal lymph nodes. An exploratory celiotomy was performed to acquire incisional biopsies of affected tissues. A diagnosis of idiopathic hypereosinophilic syndrome was made based on significant eosinophilic inflammation on histopathology of the affected structures, and exclusion of other causes of hypereosinophilia or multisystemic eosinophilic infiltration. The dog showed a strong partial response to the initial anti‐inflammatory prednisolone monotherapy (0.76 mg/kg/day) with resolution of hypereosinophilia, and clinical remission was achieved following escalation to an immunosuppressive dose (1.56 mg/kg/day). During tapering of prednisolone, the dog developed a new jejunal mass with marked eosinophilic infiltration at a different site, despite continued remission of the original lesions and absence of recurrent eosinophilia.