Acromegaly due to a somathrop adenoma in a dog

A 10-year-old intact male Dalmatian dog was referred because of gait abnormalities consisting of chronic progressive stiffness and rigidity. Other complains were polyphagia associated with weight gain, polyuria and polydipsia, and excessive panting. The owner had noticed progressive thickening of the skin and enlargement of the tongue during the last three years. In line with these observations, physical examination revealed thickening of the skin, especially at the level of the head and the neck, redundant skin folds and clear enlargement of the tongue compared to the standard of the breed. In addition, an inspiratory stridor was present. Neurological examination revealed an abnormal gait characterized by minimal tetraparesis, pacing, stiffness and slight proprioceptive defects. The only abnormalities found on routine laboratory examination were mild anaemia and increased circulating levels of CK and cholesterol. Circulating concentrations of total thyroxine, free thyroxine, and cTSH, and the results of an ACTH stimulation test were all within reference ranges. The basal plasma growth hormone (GH) concentration was markedly elevated (23 ng/ml; reference range 2-5 ng/ml) and did not decrease after glucose infusion (1g/kg b.w.) or after somatostatin administration. The plasma insulin-like growth factor-I concentration was also markedly elevated (1254 μg/L; reference range 137-425 μg /L). Abdominal ultrasonography showed no abnormalities. Survey radiographs of the vertebral column showed diffuse spondylosis extending from the cervical to the lumbar spine. CT scan of the skull showed an enlarged pituitary gland with normal enhancement pattern. The dog was dismissed without therapy. After 3 months the owner elected euthanasia because of deterioration of the gait abnormalities. On postmortem examination, the skin was about three times thicker than normal skin of this breed. The whole vertebral column appeared as a single and inflexible structure due to the presence of uniform and diffuse vertebral exostosis. Microscopic examination of the skin revealed a moderate regular epidermal hyperplasia and an increased amount in dermal collagen. An increased amount of fibrous tissue and fat cells was present in the interstitium of the myocardium. In the pituitary gland an acidophilic adenoma was found and the tumour immunostained positively for GH (and negative for ACTH and alpha-MSH). A final diagnosis of acromegaly due to a GH producing pituitary adenoma was made. To the authors’ knowledge, this is the first description of acromegaly due to a somatotroph adenoma in the dog.