Insulinomas are a type of pancreatic neuroendocrine tumor (pNET) that arises from pancreatic endocrine tissue. They are rare, with an estimated incidence of 4 cases per 1 million person-years7. While typically larger pNETs are detectable using conventional imaging studies such as transabdominal ultrasound, CT, or MRI, insulinomas are frequently missed by conventional imaging due to their relatively small size. We present the case of a 66-year-old African American male with an insulinoma undetected by contrast-enhanced MRI, that was ultimately localized and diagnosed via endoscopic ultrasound (EUS) with fine needle aspiration (FNA).

Case Presentation:

A 66-year-old African American male with past medical history of hypertension, obstructive sleep apnea, glaucoma, coronary artery disease status post coronary stents, and squamous cell carcinoma of the larynx status post total laryngectomy presented from a rehab facility with weakness, lethargy, and repeated episodes of hypoglycemia. The patient denied history of diabetes, use of oral antihyperglycemic agents, or insulin.

On arrival, the patient’s glucose level was 35-45 mg/dL on repeated testing; he was started on 10% dextrose (D10) intravenous drip to maintain normoglycemia. Fasting laboratory evaluation (Table 1) was remarkable for elevated levels of insulin, c-peptide, and proinsulin. TSH and ACTH levels were within normal limits. Morning cortisol level at 8am was low at 10.9 mcg/dL; however, cosyntropin stimulation test showed adequate response of cortisol. The patient also had elevated C-reactive protein, low ionized calcium, and a negative insulin autoantibody assay (Table 1).