Idiopathic hypereosinophilic syndrome in a female Sprague Dawley rat

An approximately 7.5-month-old female Sprague Dawley rat (<i>Rattus norvegicus</i>) housed in a research facility presented for skin lesions including multifocal crusting and hypotrichosis. On presentation the research rat was mildly underconditioned with a distended abdomen and later developed small-bowel diarrhea. Abdominal ultrasound demonstrated diffusely thickened intestinal segments, and veterinary staff palpated a linear intra-abdominal mass. The rat was unresponsive to supportive care, and the rat was euthanized and necropsied. An elongate pink-tan mesenteric mass and severe, diffuse dilation and thickening of the small intestine were observed. Histopathology revealed mild to severe inflammation in most tissues with an abundance of eosinophils and eosinophilic granulomas in the abdominal lymph nodes. Clinical and histopathological findings are similar to hypereosinophilic syndromes (HES) described in a variety of species, including humans. Previous reports of HES in rats are limited to descriptions in rat strain Matsumoto Eosinophilia Shinshu (MES), which has been used as a model of human HES. Unlike MES rats, the rat in this report had diarrhea as well as eosinophilic infiltrates in the skin and heart, all of which are commonly described in human cases of HES.