Resting and Stimulated Cortisol Concentrations in Dogs with Hypoglycemia Associated with Insulinoma
Hypoglycemia is a potent physiological stimulus for cortisol release; both insulin-producing tumors and hypoadrenocorticism can result in moderate to severe hypoglycemia. A recent study reported that hypoadrenocorticism may be practically excluded, without an ACTH-stimulated cortisol concentration, if the resting cortisol concentration was > 2 µg/dl. (Lennon et al, JAVMA 2007 231:413-416) The purpose of this study was to evaluate the resting and ACTH-stimulated cortisol concentrations in hypoglycemic dogs that were subsequently established to have an insulinoma as the cause of their hypoglycemia. The hypothesis was that severe hypoglycemia due to insulinoma would result in a marked increase in basal cortisol concentrations and that resting plasma cortisol concentration > 2 µg/dl would preclude the need for ACTH stimulation testing.
The medical records of the Foster Hospital for Small Animals (FHSA) and the Queen Mother Hospital for Animals (QMHA) were searched for dogs with a confirmed diagnosis, by both histopathology and a positive insulin/glucose ratio, of insulinoma.
Eight dogs were identified with insulinoma that also had an ACTH stimulation test performed during diagnostic testing. The dogs were a variety of breeds with a mean age of 8.9 ± 1.9 years. The mean glucose value was 42.4 ± 12.3 mg/dl. The basal cortisol concentration was 4.8 ± 3 µg/dl and all dogs had a normal response to ACTH stimulation with a mean stimulated cortisol concentration of 15.3 ± 6.2 µg/dl. Two dogs (25%) had a basal cortisol of < 2 µg/dl (1.5 µg/dl and 1.8 µg/dl). There was no correlation between blood glucose and basal cortisol.
Dogs with insulinoma have a normal, not supraphysiologic, basal cortisol concentration, and ACTH-stimulated cortisol responses are appropriate. A basal cortisol level < 2 µg/dl is not sufficient to identify inadequate adrenal function in dogs with hypoglycemia. Therefore an ACTH stimulation test is warranted in dogs with unexplained hypoglycemia, especially when both hypoadrenocorticism and insulinoma remain possible diagnoses.