A 28-year-old white woman, KR, presents to primary care with episodic diaphoresis and weakness that occur one to two hours after meals. There is no history of syncope or seizures. The hypoglycemic symptoms abate with intake of oral glucose and do not occur when the patient fasts.
KR underwent Roux-en-Y gastric bypass surgery 12 months ago. At the time, her body weight was 250 lbs and her height, 62 in (BMI, 46). She has lost 60 lbs since surgery (current BMI, 35). KR has no comorbid medical conditions. She denies use of insulin injection or oral hypoglycemic medication, as well as alcohol consumption. There is no history of diarrhea or abdominal pain. Her only medication is a daily multivitamin.
Physical exam reveals a blood pressure of 126/80 mm Hg; pulse, 82 beats/min; respiratory rate, 16 breaths/min; and O2 saturation, 98%. Heart rate is regular with no murmur. Lungs are clear to auscultation. Abdominal and neurologic exams are unremarkable; musculoskeletal strength and orthostatic vital signs are normal.
The patient is instructed to test her blood sugar with a glucometer and return to the clinic in two weeks. Fingerstick monitoring reveals that her serum glucose level drops into the 40 to 50 mg/dL range approximately one to two hours after meals containing > 45 g of carbohydrate. Her fasting serum glucose readings are in the 80 to 95 mg/dL range.
The patient is presumptively diagnosed with dumping syndrome and receives nutritional counseling; she is instructed to reduce intake of simple carbohydrates and increase the protein content of meals. Despite these dietary modifications, the episodes of hypoglycemia persist.
The patient is then referred to endocrinology. Fasting labwork reveals a serum glucose level of 85 mg/dL; normal adrenocorticotropic hormone (ACTH) and cortisol levels; C-peptide level, 2.46 ng/mL (reference range, 0.80–4.00 ng/mL); and insulin level, 6.4 mIU/mL (reference range 2.6–24.9 mIU/mL). A 75-g two-hour oral glucose tolerance test (OGTT) reveals peak serum glucose of 180 mg/dL at 30 minutes followed by a nadir serum glucose of 48 mg/dL at 110 minutes, accompanied by hypoglycemic symptoms. The insulin and C-peptide levels are elevated during the entire two-hour test. The serum cortisol level is 22 mg/dL when the glucose level is 48 mg/dL. CT of the abdomen, previously ordered by the patient’s primary care provider, was unremarkable.
Since there is no laboratory evidence of fasting hypoglycemia and no pancreatic abnormalities are seen on imaging studies, the possibility of insulinoma is excluded from the differential diagnosis. Adrenal insufficiency is excluded based on the normal ACTH and cortisol levels. The possibility of noninsulinoma pancreatogenous hypoglycemia syndrome is considered.
The patient is prescribed verapamil ER 100 mg/d and notes significant reduction in the frequency of hypoglycemic episodes and symptoms. She is scheduled for follow-up in four weeks to assess for any changes in the frequency or severity of her hypoglycemic episodes.
BACKGROUND
Postprandial hypoglycemia is a rare but potentially serious complication of bariatric surgery procedures that divert nutrients into the small bowel.1,2 The Bariatric Outcomes Longitudinal Database revealed a 0.1% incidence of hypoglycemia in patients who underwent Roux-en-Y gastric bypass surgery.3
The most common cause of hypoglycemia following gastric bypass surgery is dumping syndrome, which involves rapid emptying of gastric contents with reactive hypoglycemia due to increased postprandial insulin release. In dumping syndrome, hypoglycemic symptoms—flushing, diaphoresis, weakness, and dizziness—typically occur within two to three hours after meals; patients do not experience the more severe symptoms of neuroglycopenia (eg, cognitive impairment, seizures, and loss of consciousness).4 The symptoms of dumping syndrome typically improve with reduced intake of simple carbohydrates and increased protein consumption.1
Other causes of postprandial hypoglycemia include insulinoma and noninsulinoma pancreatogenous hypoglycemia syndrome (NIPHS). Although both diagnoses are rare, they should be considered if no improvement in hypoglycemic symptoms occurs after dietary modification.1
Insulinoma is the most common cause of persistent hyperinsulinemic hypoglycemia. It is defined by Whipple’s triad: symptomatic hypoglycemia during fasting, a serum glucose level > 50 mg/dL at the time of symptom onset, and relief of symptoms after administration of glucose.5
NIPHS is less common than insulinoma. It is characterized by postprandial hypoglycemia due to increased insulin secretion resulting from pancreatic b-cell hyperplasia. Hypoglycemia does not typically occur during a 72-hour fast. In addition, pancreatic imaging studies yield normal results in cases of NIPHS. The selective arterial calcium stimulation test is positive in NIPHS.5 NIPHS is definitively diagnosed by histopathologic examination of the pancreas, which reveals nesidioblastosis.6
Nesidioblastosis involves pathologic b-cell overgrowth in the pancreas that results in excess insulin secretion.4 Nesidioblastosis is characterized by pancreatic b-cell hypertrophy, islet hyperplasia, and increased b-cell mass.2
Nesidioblastosis is the leading cause of hyperinsulinemia in newborns and infants (annual incidence, 1 in 50,000 births) but is quite rare in adults, occurring in 0.5% to 7.0% of all those with hyperinsulinism.7,8 Islet cell hypertrophy—characteristic of nesidioblastosis—is seen in both adults and children, whereas genetic mutations are present only in infants.7
Although rare in adults, nesidioblastosis is more common in the setting of gastric bypass than in the general population.7 As of 2011, there have been 40 cases of nesidioblastosis in adults who received gastric bypass.2 With the rapid increase in the number of these surgeries performed each year, nesidioblastosis should be considered in the differential diagnosis for patients who experience hypoglycemia following the procedure.2,7
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