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Insulinoma in Elderly Man

Insulinoma in Elderly Man

A 75-year-old man is brought to the emergency department (ED) after awakening in the night very confused and disoriented. His wife had called 911; when the paramedics arrived, they found his blood glucose level to be 36 mg/dL. Intravenous dextrose was administered on the way to the hospital. In the ED, he is fully awake, lucid, and oriented. A second blood glucose level is 90 mg/dL.


The patient has had several similar episodes over the past year; all of these occurred within 2 to 3 hours of a large meal. He denies any change in weight, bowel habits, or appetite. He has a history of bilateral knee replacement and hernia but no diabetes, coronary artery disease, hypertension, or other major medical diagnosis. His only medications are a multivitamin supplement and occasionally acetaminophen. His grandfather had type 2 diabetes mellitus.


Temperature is 37°C (98.6°F); heart rate, 68 beats per minute; and blood pressure, 138/84 mm Hg. Head, ears, eyes, nose, and throat are normal. No carotid bruits or enlarged lymph nodes are detected. Chest is clear and heart rhythm is regular, without murmurs or gallops. Abdomen is nontender, with no masses or organomegaly. Results of a detailed neurological examination are normal.


Results of a chemistry panel are normal (including a creatinine level of 0.9 mg/dL and a blood glucose level of 114 mg/dL). A hemogram is also normal.

Which of the following studies would be most likely to yield a definitive diagnosis?
A. Measurement of a fasting cortisol level followed by an adrenocorticotropic
hormone (ACTH) stimulation test.
B. Abdominal CT.
C. Measurement of plasma catecholamine and calcitonin levels.
D. A 72-hour fast with simultaneous measurements of blood glucose, plasma insulin, C-peptide, and proinsulin levels.

(answer on next page)


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