Insulinoma presenting with postprandial hypoglycemia and a low body mass index: A case report

Abstract

Background: Insulinomas are the most common type of functioning endocrine neoplasms of the pancreas presenting hypoglycemic symptoms. Patients characteristically develop symptoms while fasting, but some patients have reported symptoms only in the postprandial state. Repeated and prolonged hypoglycemic episodes can reduce the awareness of adrenergic symptoms, and patients may have amnesia, which delays diagnosis.

Case summary: We describe a case of a 24-year-old underweight patient who showed hypoglycemic symptoms for almost 6 years. Although patients with insulinoma characteristically develop symptoms while fasting, this young man had hypoglycemic symptoms up to one hour postprandially, especially after high-sugar meals and after physical activity. The fasting tests and imaging methods performed at local hospitals were evaluated as negative for abnormal results. However, brown adipose tissue exhibited increased metabolic activity, and some muscle groups had histological changes as indicated by positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography. Glycogen deficiency was also histologically confirmed. The patient's symptoms progressed over the years and occurred more frequently, i.e., several times a month, and the patient had reduced awareness of adrenergic symptoms. The follow-up fasting test was positive, and the imaging results showed a tumor in the head of the pancreas. The patient underwent laparotomy with enucleation of the insulinoma.

Conclusion: Weight gain and fasting hypoglycemia are not necessarily characteristics of insulinoma. In prolonged cases, adrenergic symptoms can be suppressed.

Keywords: Brown adipose tissue; Case report; Glycogen deficit; Hypoglycemia; Insulinoma; Underweight.

Figure 1

Positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose integrated with computed tomography showing enhanced metabolic activity of brown adipose tissue in the neck, paravertebral, supra- and infraclavicular, axillar, mediastinal, jugular, diaphragmatic, and perinephric regions bilaterally (white arrows) and several muscle groups (e.g., psoas major muscles) (orange arrows).

Figure 2

Insulinoma (perioperative findings). A: Insulinoma as indicated by the yellow arrows was located in the upper part of the pancreatic head; B: Detailed view of the whole enucleated insulinoma; C: Detailed view of the sectioned insulinoma.

Figure 3

Histological and immunohistochemical findings of the insulinoma and histological findings of muscle biopsy. A: Positive insulin immunostaining; B: Hematoxylin and eosin staining; C: Positive synaptophysin immunostaining; D: Glycogen deficit (light violet areas) in muscle syncytia (musculus quadriceps femoris), PAS stain, 20 ×.