A 55-year-old man with type 2 diabetes reports fasting capillary glucose readings of 90 to 100 mg/dL but pre-breakfast clinic values of 190 mg/dL. His bedtime basal insulin was recently increased. A 3 AM capillary glucose is 130 mg/dL. What explains the morning hyperglycemia?
- A Dawn phenomenon due to early morning hormonal counter-regulation ✓
- B Somogyi phenomenon with nocturnal hypoglycemia
- C Excessive carbohydrate intake at breakfast
- D Insulin injection into hypertrophied lipodystrophic tissue
Correct answer: A. Dawn phenomenon due to early morning hormonal counter-regulation
Explanation
The 3 AM glucose of 130 mg/dL excludes nocturnal hypoglycemia, which is the defining feature of the Somogyi phenomenon, where rebound hyperglycemia follows untreated nighttime lows. Here the rise begins before breakfast without any preceding dip, consistent with the dawn phenomenon driven by the early morning surge of growth hormone and cortisol increasing hepatic glucose output. The correct response is adjusting the basal insulin dose or its timing, not reducing it.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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