Factitious Hypoglycemia Caused by a Unique Pattern of Drug Use

Factitious hypoglycemia, caused by the surreptitious use of insulin and sulfonylureas, is one of the most challenging differential diagnoses of hypoglycemia. Diagnosis is usually established via exclusion with respect to the special patterns of plasma insulin and C-peptide during hypoglycemic episodes.
We report a case of recurrent hypoglycemic episodes and confusing patterns of insulin and C-peptide levels. In the primary evaluations, insulinoma was suspected considering the high plasma concentrations of insulin and C-peptide, besides negative urine and plasma sulfonylureas during hypoglycemic episodes. Considering the normal imaging studies and refractory hypoglycemia to medical therapy, distal pancreatectomy was performed. The patient had no episodes of hypoglycemia after the surgery. Five months later, similar episodes recurred. Further investigations revealed different plasma concentrations of insulin and C-peptide in each hypoglycemic episode. Regarding various biochemical patterns during hypoglycemia and absence of evidence supporting other differential diagnoses, we suspected factitious causes. Close observation revealed that the patient had a history of intermittent glyburide consumption and analog insulin injection.
Most commercial insulin immunoassays can only detect human insulin and lack the ability to identify synthetic analog insulin. In addition, common detection methods for sulfonylureas and meglitinides are of low diagnostic value in the human plasma and urine. These laboratory defects can lead to the misdiagnosis of insulinoma or noninsulin-mediated hypoglycemia due to the surreptitious use of insulin secretagogues or analog insulin, respectively. Therefore, due to the lack of any definitive laboratory findings, clinical suspicion is the best strategy for diagnosis.