Somogyi Effect
(Rebound Hyperglycaemia)

An insulin dose that is too high may bring about the Somogyi effect or rebound hyperglycaemia. This can also be produced if blood glucose concentrations fall too rapidly.

The body attempts to counteract the decline in the blood glucose concentration through a chain of reactions:

• The blood glucose concentration falls rapidly or approaches hypoglycaemia (blood glucose concentrations of less than 5 mmol/l (90 mg/dl)) following the injection of insulin. The animal becomes hungry and either restless or lethargic.
• In response to a declining blood glucose concentration in the CNS, adrenaline and subsequently cortisol, glucagon and growth hormone are released.
• These hormones bring about an increase in the blood glucose concentration (through gluconeogenesis, release of glucose from hepatic glycogen and increased peripheral resistance to insulin).
• The resultant hyperglycaemia produces polyuria and polydipsia. This can easily be misinterpreted as a result of an inadequate insulin dose.

If the morning polyuria is thought to be the result of an insufficient insulin dose and a higher dose is given, the problem will be aggravated. An even more pronounced Somogyi effect will follow. Eventually the counter-regulatory mechanisms become exhausted resulting in severe hypoglycaemia.

Hyperglycaemia due to a Somogyi effect can sometimes persist for as long as 3 days after a single hypoglycaemic episode. As a result blood glucose concentrations do not always normalise within a few days of lowering the insulin dose.

If the Somogyi effect is suspected, an alternative approach is to decrease the dose by 20% and closely observe the clinical signs. If signs of polyuria or polydipsia worsen a few days following the dose adjustment, it is unlikely that the Somogyi effect was the cause of the regulation problems. Conversely, if the polyuria and polydipsia disappear within a few days it is probable that the Somogyi effect was the cause.

Diagnosis

A blood glucose curve is the only diagnostic tool that can be used to detect a Somogyi effect.

Either of the following blood glucose curves indicate Somogyi effect:

• Hypoglycaemia (low nadir) followed by rebound hyperglycaemia.
• A rapid decrease in glycaemia with an adequte nadir followed by rebound hyperglycaemia.

See the following two graphs for examples of blood glucose curves in a case of rebound hyperglycaemia. Insulin was injected at time 0 hours.

Blood glucose curves

See blood glucose curves for details on making a glucose curve.

See blood glucose curves for details on making a glucose curve.