Hypersomatotropism with associated acromegaly is increasingly considered one of the primary causes of insulin resistance in cats with diabetes mellitus (DM). Acromegaly is the syndrome that occurs from excessive production of growth hormone (GH) from a functional somatotropic adenoma of the pituitary gland. GH leads to a postreceptor defect in the action of insulin on target cells. This action leads to decreased carbohydrate utilization, reduced insulin sensitivity and hyperglycemia. An additional result of excessive GH is production of IGF-1, primarily by the liver, leading to increased protein synthesis and excessive tissue growth.
Physical characteristics commonly reported include weight gain, prominent facial features, arthropathy, respiratory stridor and organomegaly. Diagnosis usually relies on noting the physical changes typical for the syndrome, increased serum IGF-1 concentrations and demonstration of insulin resistant DM. Along with unresolved clinical signs of DM, poor regulation of DM is considered to occur if insulin doses administered are ≥ 5 IU/injection or ≥ 1 IU/kg/injection.
Researchers performed a retrospective case control study of medical records of cats presenting at two veterinary university hospitals from January 2002 and October 2012. The objective of the study was to see if changes in selected organs on abdominal ultrasound of acromegalic cats could be used to increase suspicion for this disorder. Twenty-four cats were included in the acromegaly group if they had evidence of insulin resistant DM, increased serum IGF-1 concentrations and had an abdominal ultrasound examination performed. A control group of twenty-four aged matched cats was used that also had an abdominal ultrasound examination performed for disease unlikely to involve the kidneys, adrenal glands, pancreas or liver.
The results of the ultrasonographic examinations were that cats with acromegaly had significantly increased median left and right kidney length, median left and right adrenal gland thickness and pancreatic thickness. Enlargement of the liver and both adrenal glands were found in 63% and 53% of acromegalic cats, respectively, and none of the controls. Abnormalities of the pancreas were noted in 88% of cats with acromegaly and 8% of the controls.
Therefore, acromegalic cats have measurably enlarged kidneys, adrenal glands, a subjectively enlarged liver compared with age-matched cats that did not have acromegaly. The recommendation is to measure serum IGF-1 concentrations in insulin resistant diabetic cats that exhibit enlargement of these organs on abdominal ultrasound examination.
