CPB 697 RESEARCH SEMINAR

DEPARTMENT OF COMPARATIVE PATHOBIOLOGY

Ikki Mitsui, BVM

Graduate Student in Anatomic Pathology

Department of Comparative Pathobiology

Purdue University

“Hypertrichosis In A Horse With Alimentary T-cell Lymphoma And Pituitary Involvement”

Thursday, March 1, 2007

VPTH 112

3:30 p.m.

Abstract:

Equine alimentary lymphoma involves the small intestine more commonly than the large intestine. Other organs that may be affected are the liver and mesenteric lymph nodes. Equine lymphoma involving the central nervous system is rare and, to our knowledge, pituitary involvement has not been reported.

A 13-year-old Quarterhorse mare with a 6-month history of diarrhea, progressive weight loss, and lethargy was presented to Purdue University Veterinary Teaching Hospital. An initial diagnosis of protein-losing enteropathy was made. A diagnosis of T-cell lymphoma was made from a rectal biopsy with immunohistochemistry for CD3 (T-cell marker), CD20 and CD79a (B-cell markers). Because the mare had not shed its winter haircoat the previous summer (hypertrichosis), a diagnosis of pituitary pars intermedia dysfunction (PPID) was considered. The clinical condition (lymphoma) did not improve with immunosuppressive therapy and it was euthanized.

Necropsy findings included hypertrichosis, focal duodenal mucosal hyperemia, and pituitary gland enlargement (2.9 x 2.5 x 2.3 cm), which was homogeneously tan. Histologically, neoplastic lymphocytes infiltrated the lamina propria and submucosa of the stomach, small intestine, and large intestine. Neoplastic lymphocytes also diffusely infiltrated mesenteric lymph nodes and the pituitary gland. Neoplastic lymphocytes in the pituitary gland and other organs were CD3-positive (T-cell lymphoma).

Hypertrichosis is a consistent clinical feature of PPID. The exact pathogenesis of PPID-related hypertrichosis is unclear. Several hypotheses include: 1) excessive adrenocortical production of sex hormones; 2) increased secretion of melanocyte stimulating hormone from the pituitary pars intermedia through loss of dopaminergic inhibition; 3) mechanical pressure of the pituitary gland on the hypothalamic thermoregulatory center. Pituitary adenoma was not observed in the mare. Hypertrichosis in the present case could have been triggered by enlargement of the pituitary gland secondary to lymphoma and mechanical pressure on the hypothalamic thermoregulatory center.

Primary lymphoma of the pituitary gland has rarely been reported in humans. Human cases are mostly of large B-cell type. The present case is the first report of lymphoma affecting the pituitary gland of horses or other domestic species.