Differential Diagnosis for the Patient's Symptoms

The patient presents with episodes of dizziness, weakness, palpitations, and low blood glucose levels, which resolve with intravenous dextrose administration. The elevated serum insulin and C-peptide levels prior to dextrose administration provide crucial clues for the differential diagnosis.

• Single Most Likely Diagnosis

  • Surreptitious sulfonylurea use: This is the most likely diagnosis given the patient's symptoms of hypoglycemia, elevated insulin and C-peptide levels, and the absence of other clear causes for these findings. Sulfonylureas stimulate insulin release from the pancreas, which can lead to hypoglycemia. The patient's access to sulfonylureas could be related to her father's diabetes, making this a plausible explanation.

• Other Likely Diagnoses

  • Exogenous insulin administration: Although less likely than sulfonylurea use due to the elevated C-peptide levels (which would be low in exogenous insulin administration), it remains a consideration. However, the presence of elevated C-peptide suggests endogenous insulin production.
  • Restriction of caloric intake: Given the patient's low BMI and the context of studying for exams, severe caloric restriction could lead to hypoglycemia. However, this would not typically cause elevated insulin and C-peptide levels.

• Do Not Miss Diagnoses

  • Insulinoma: A rare tumor of the pancreas that produces excess insulin, leading to hypoglycemia. Although unlikely, missing this diagnosis could have significant consequences, including persistent hypoglycemia and the need for surgical intervention.
  • Binge drinking of alcohol: Alcohol can induce hypoglycemia, especially in fasting individuals. While the patient reports only occasional alcohol use, it's essential to consider this possibility, especially if other explanations are ruled out.

• Rare Diagnoses

  • Phentermine use: Certain medications like phentermine can affect appetite and potentially lead to hypoglycemia through severe caloric restriction, but this would not explain the elevated insulin and C-peptide levels.
  • Self-induced vomiting: Part of the differential for unexplained hypoglycemia, especially in the context of eating disorders. However, this would not directly cause elevated insulin and C-peptide levels.
  • Other rare causes of hypoglycemia: Including genetic disorders affecting glucose metabolism, hormone deficiencies (e.g., adrenal insufficiency), and certain medications not mentioned here. These are less likely given the patient's presentation and the specific findings of elevated insulin and C-peptide levels.