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Summary
An 89-year-old woman presented with a 6-year history of occasional episodes of impaired consciousness that were relieved by ingestion of a snack. Three months before presenting to our hospital, she had been hospitalized in a local hospital with subdural hematoma caused by a head contusion, where previously unrecognized hypoglycemia was discovered. Fasting plasma glucose concentration was 37 mg/dL, with a relatively high serum level of insulin (34.9 µU/mL). Computed tomography showed a 14 mm hyperenhancing tumor in the tail of the pancreas and she was referred to our hospital for further investigation. A prolonged fasting test revealed the plasma glucose concentration reduced to 43 mg/dL (2.4 mmol/L) at 8 h after the last meal. Serum insulin, proinsulin, and C-peptide concentrations were 21.1 µU/mL, 16.9 pmol/L, and 2.72 ng/mL, respectively. Subsequent intravenous administration of 1 mg of glucagon increased the plasma glucose concentration to 76 mg/dL (4.2 mmol/L). Moreover, the insulin-to-C-peptide molar ratio was 0.14. These data indicated the presence of insulinoma. Interestingly, serum anti-insulin antibodies were elevated (21.1 U/mL), although she had no history of taking exogenous insulin injection, alpha lipoic acid, or sulfhydryl group-containing agents. Human leukocyte antigen (HLA) typing revealed HLA-DRB1*0407 and HLA-DRB1*1405 alleles. Treatment with diazoxide prevented hypoglycemia, but was discontinued due to weight gain and leg edema. Elevated serum anti-insulin antibodies persisted almost 1 year after the diagnosis of insulinoma. We present a rare case of insulinoma concomitant with serum anti-insulin antibodies.
Learning points
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Insulinoma presenting with concomitant anti-insulin antibodies appears rare.
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Insulin/C-peptide molar ratio and serum insulin concentration are useful for differentiating insulinoma and autoimmune syndrome.
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Flash glucose monitoring systems appear suitable for evaluating treatment outcomes.
Search for other papers by Rikako Nakajima in
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Summary
Unawareness of postprandial hypoglycemia for 5 years was identified in a 66-year-old man at a local clinic. The patient was referred to our hospital because of this first awareness of hypoglycemia (i.e. lightheadedness and impaired consciousness) developing after lunch. In a 75 g oral glucose tolerance test, the plasma glucose concentration was decreased to 32 mg/dL (1.8 mmol/L) at 150 min with relatively high concentrations of insulin (8.1 μU/mL), proinsulin (70.3 pmol/L), and C-peptide (4.63 ng/mL). In a prolonged fasting test, the plasma glucose concentration was decreased to 43 mg/dL (2.4 mmol/L) at 66 h with an insulin concentration of 1.4 μU/mL and a C-peptide concentration of 0.49 ng/mL. Computed tomography showed an 18 mm hyperenhancing tumor in the uncinate process of the pancreas. A selective arterial calcium stimulation test showed an elevated serum insulin concentration in the superior mesenteric artery. The patient was then diagnosed with insulinoma and received pancreaticoduodenectomy. Continuous glucose monitoring (CGM) using the Dexcom G6 system showed unawareness of hypoglycemia mainly during the daytime before surgery. When the sensor glucose value was reduced to 55 mg/dL (3.1 mmol/L), the Dexcom G6 system emitted an urgent low glucose alarm to the patient four times for 10 days. Two months after surgery, an overall increase in daily blood glucose concentrations and resolution of hypoglycemia were shown by CGM. We report a case of insulinoma with unawareness of postprandial hypoglycemia in the patient. The Dexcom G6 system was helpful for assessing preoperative hypoglycemia and for evaluating outcomes of treatment by surgery.
Learning points
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Insulinoma occasionally leads to postprandial hypoglycemia.
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The CGM system is useful for revealing the presence of unnoticed hypoglycemia and for evaluating treatment outcomes after surgical resection.
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The Dexcom G6 system has an urgent low glucose alarm, making it particularly suitable for patients who are unaware of hypoglycemia.
