Fasting Hyperglycemia and Associated Free Insulin and Cortisol Changes in “Somogyi-Like” Patients

Blood glucose levels were measured over a 24-h period in eight insulin-dependent diabetic subjects who were difficult to control and who presented with morning fasting hyperglycemia. At least seven exhibited clinical characteristics suggestive of the Somogyi phenomenon. A continuous glucose monitoring apparatus was used to relate the concentrations of glucose during the day to concomitant levels of free insulin and cortisol. In all patients a significant (P < 0.01) rise in fasting morning glucose started at about 0600 h, while they were still asleep. In six patients the morning elevation of blood glucose was preceded by stable, almost normal glucose levels during the night (117 ± 2.5 mg/dl); one of the two remaining patients (no. 7) exhibited high overnight glucose levels (268 ± 7.2 mg/dl), whereas the other (no. 8) had a mild hypoglycemic episode (45 mg/dl) 6 h before the hyperglycemic period. In all patients the fasting glucose rise was associated with the usual morning cortisol surge (P < 0.05) and with a significant decrease in the concentration of serum free insulin (P < 0.01). The free insulin levels in patient no. 8 were higher, while those of patient no. 7 were lower, than in the other six patients. We conclude that the diurnal morning rise in cortisol may cause hyperglycemia in insulindependent diabetic patients if insufficient exogenous insulin remains and/or endogenous insulin is not secreted. In such patients the high levels of fasting glucose in the morning may misrepresent their overnight control of blood glucose and lead to an erroneous impression of the Somogyi phenomenon.