Acromegaly is a chronic syndrome, characterized by overgrowth of connective tissue, bone, and viscera due to growth hormone (GH) hypersecretion in adulthood. This syndrome is known to occur in humans, dogs, and cats, but the pathogenesis differs completely in these species. In humans and cats, the excessive GH secretion is caused by a somatotroph adenoma of the pituitary gland [1] and [2]. In dogs, the GH excess originates from an extra-pituitary site [3]. In female dogs either endogenous progesterone (metoestrus) or exogenous progestins (used for oestrus prevention) may give rise to hypersecretion of GH in the mammary gland, resulting in acromegaly and glucose intolerance [3], [4] and [5].
So far, there is no conclusive evidence that pituitary tumours give rise to GH hypersecretion in dogs. There are two reports of pituitary tumours, one in a 9-year-old male English Bulldog with thickened cranial bones [6], and one in a 5-year-old male Boston Terrier with diabetes mellitus supposedly due to GH excess [7]. In both cases, GH hypersecretion was not demonstrated and immunohistochemistry of the pituitary tumours was not performed. More recently, immunohistochemical staining for GH revealed a somatotroph adenoma in a 9-year-old male Doberman Pinscher with severe insulin-resistant diabetes mellitus [8]. However, no acromegalic features were observed and circulating levels of GH and insulin-like growth factor-1 (IGF-1) were not measured.
Here we report on the physical, endocrine and (histo)pathological findings in a male dog with acromegalic changes and insulin resistance due to a GH-secreting pituitary adenoma. To the authors’ knowledge, this case report is the first description of excessive GH secretion due to a somatotroph adenoma in a dog.