A case of insulinoma misidentified as schizophrenia due to its manifestation in neuropsychiatric symptoms

Insulinomas can present with neuroglycopenic symptoms suggesting neuropsychiatric disorders, delaying diagnosis and treatment. We recently treated a 65-year-old woman with insulinoma who was misdiagnosed at her nearby psychiatric clinic as having schizophrenia because of personality changes and memory impairment; she was treated with brexpiprazole, which was discontinued due to persistence of the symptoms. Despite her relatively low casual plasma glucose (70 mg/dL), the physician at the psychiatric clinic did not investigate the possibility of hypoglycemia, partly because her HbA1c level (5.2%) was within normal range. After skipping lunch one day, she was found by her family to be unable to communicate properly. She was transported to the emergency room of our hospital, where intermittently scanning continuous glucose monitoring (isCGM) use permitted detection of the hypoglycemia and led to a diagnosis of insulinoma and successful resection. A 72-h fasting test established hyperinsulinemic hypoglycemia. Contrast-enhanced computed-tomography and endoscopic ultrasonography together with selective arterial calcium stimulation test revealed an insulin-secreting tumor in the tail of the pancreas. Surgical resection of the tumor corrected her glucose and insulin levels as well as eliminated the insulinoma neuropsychiatric symptoms. Pathological examination showed that the tumor was positive for chromogranin A, synaptophysin and insulin. It is, therefore, important for physicians to be aware that insulinomas can manifest as neuroglycopenic symptoms and to consider the possibility of hypoglycemia by careful medical interview and isCGM, especially when patients suspected of psychiatric disorders do not show the expected response to antipsychotic drugs.