Hypersomatotropism and Hypercortisolism Caused by a Plurihormonal Pituitary Adenoma in a Dog

A 12-year-old, male Labrador Retriever was presented because of polyuria, polydipsia, polyphagia, joint pain, and physical features consistent with acromegaly. Circulating insulin-like growth factor-1 (IGF-1) concentration was increased (> 1000 ng/mL; reference interval [RI], 42-449), suggestive of hypersomatotropism. An abnormal low-dose dexamethasone suppression test and increased circulating adrenocorticotropic (ACTH) concentration indicated pituitary-dependent hypercortisolism. Computed tomography identified an enlarged pituitary gland. Treatment with cabergoline initially decreased circulating IGF-1 and ACTH concentrations and urinary cortisol-to-creatinine ratio (UCCR), with a notable reduction in acromegalic physical features. However, 7 months after the start of cabergoline treatment, IGF-1, ACTH, and UCCR had increased again, although pituitary gland size remained stable. Because of worsening joint pain, euthanasia was performed. On necropsy, double immunohistochemistry identified pituitary tumor cells with cytoplasmic co-expression of both growth hormone (GH) and ACTH, consistent with a monomorphic plurihormonal macroadenoma. This case shows that concurrent hypersomatotropism and hypercortisolism can occur in dogs caused by a plurihormonal pituitary adenoma.