Rebound Hyperglycemia

Rebound hyperglycemia, or the Somogyi effect, is defined as hyperglycemia resulting from insulin-induced hypoglycemia. Some studies in diabetic humans have challenged the concept of rebound hyperglycemia and suggested that hyperglycemia may instead be related to inadequate duration of insulin action coupled with release of growth hormone.

This study investigated the prevalence of rebound hyperglycemia in a cohort of diabetic cats managed with a single treatment protocol in their home environment. Owned diabetic (n = 55) cats were treated with glargine to regulate blood glucose concentration and were exclusively fed a low-carbohydrate diet. Blood glucose was measured a median of 5 times per day for a median of 101 days. Rebound hyperglycemia was defined as hyperglycemia following an episode of hypoglycemia with or without clinical evidence of insulin resistance. 

Out of 10 767 total curves, 45 were consistent with rebound hyperglycemia, only 4 of which were associated with insulin resistance. Eight hundred seventy-six hypoglycemic nadirs were measured that were not then followed by rebound hyperglycemia. In each episode of rebound hyperglycemia, the cat was fed a small meal of high-carbohydrate food following the hypoglycemic event. The median peak blood glucose concentration following a hypoglycemic nadir (371 mg/dL) was not significantly different from that following a normoglycemic nadir (374 mg/dL). The insulin dose did not influence the prevalence of rebound hyperglycemia.  

The authors concluded that rebound hyperglycemia associated with persistent marked insulin resistance in glargine-treated diabetic cats is rare; rebound hyperglycemia without persistent insulin resistance is more common but still infrequent. The authors recommended that the insulin dose not be reduced when there is hyperglycemia without preceding hypoglycemia.

One constant concern in the management of diabetic cats is the possibility of insulin overdose causing rebound hyperglycemia. This possibility is potentially problematic, as it may appear clinically that the cat is not responding to insulin (or is responding poorly) and can result in inadvertent administration of higher than necessary doses of insulin, poor diabetic control, and, potentially, hypoglycemic crises.

Despite the common concern about rebound hyperglycemia, few studies have evaluated its importance or prevalence in diabetic cats, which is why this study is so valuable. The finding of rebound hyperglycemia with insulin resistance in only 1 of 240 glucose curves (with other cases of hypoglycemia not being associated with insulin resistance) certainly challenged the notion that this is a common occurrence in diabetic cats. 

As the authors suggested, continuous glucose monitoring would provide more robust data to interpret, and it would be interesting to see if the same findings accompany the use of shorter-acting (eg, Lente) insulins as well as glargine insulin. Still, these important findings suggested that rebound hyperglycemia with insulin resistance is likely to be uncommon.

—Andy Sparkes, BVetMed, PhD, DECVIM-MRCVS, International Cat Care, United Kingdom