A 10-year-old uncastrated male Dalmatian dog was referred for gait abnormalities consisting of chronic progressive stiffness and rigidity. Other symptoms were
polyphagia associated with
weight gain,
polyuria and
polydipsia, excessive panting, and an inspiratory
stridor. The owner had noticed progressive thickening of the skin and enlargement of the tongue over the last 3 years. Physical examination revealed thickening of the skin, redundant skin folds, and enlargement of the tongue. The only remarkable abnormalities found on routine laboratory examination were mild anaemia and an increased serum
fructosamine concentration. Circulating concentrations of total
thyroxine, free
thyroxine, and cTSH, and the results of an
ACTH stimulation test were all within reference ranges. The basal serum
growth hormone (GH) concentration was markedly elevated (23microg/l) and did not decrease during a
glucose tolerance test or after
somatostatin administration. The serum
insulin-like growth factor-1 concentration was also markedly elevated (1254microg/l). Basal serum
insulin concentration was high (95mU/l) and
insulin concentrations increased considerably after
glucose loading, consistent with
insulin resistance. Abdominal ultrasonography showed no abnormalities. Survey radiographs of the vertebral column showed severe
spondylosis deformans extending from the cervical to the lumbosacral spine. CT scanning of the skull showed an enlarged pituitary gland with normal enhancement pattern. On post-mortem examination, the entire vertebral column appeared as a single and inflexible structure due to the presence of multiple fused
osteophytes. The pituitary gland contained an
acidophilic adenoma that immunostained positively for GH (and negatively for
ACTH and
alpha-MSH). In conclusion, this Dalmatian dog with
acromegaly and
insulin resistance represents the first case of GH hypersecretion proven to be due to a
somatotroph adenoma.