A diagnostic dilemma: Insulinoma presenting with normal insulin and c-peptide levels in a thin, lean female

Insulinoma is a rare pancreatic neuroendocrine tumor, known for its elusive nature, often resulting in delayed diagnosis. Patients typically present with classic symptoms of hypoglycemia; however, gradually, they may adapt to persistently low blood glucose levels, resulting in blunted adrenergic responses. This adaptation can mask key symptoms and lead to a misleading clinical picture. Both body habitus and specific biochemical tests may also present challenges in establishing a diagnosis. We report a case of an insulinoma that exhibited atypical clinical features, unusual laboratory results, and remarkable adaptation to severe hypoglycemia, resulting in neurological manifestations and a prolonged diagnostic delay. A 48 years old female patient presented with occasional neurological episodes of unconsciousness and slurred speech. Three years prior, she reported multiple episodes of diaphoresis, lightheadedness with feelings of anxiety and nervousness. She sought her primary care physician and was found to have severe fasting and postprandial hypoglycemia. Over time, these symptoms became less severe and then vanished. She was symptom-free for the next two years and then she began to have infrequent episodes of unconsciousness with slurring of speech, mimicking cerebrovascular events. No neurological etiology was identified to explain her presentation and it was suspected that her symptoms were due to severe hypoglycemia. So, a series of biochemical investigations were performed to determine the underlying cause of hypoglycemia, but they yielded inconclusive results. Contrast enhanced computed tomography of abdomen revealed a pancreatic lesion later confirmed as an insulinoma. She underwent surgical enucleation, which led to significant clinical improvement. In conclusion, this case report demonstrates that insulinomas may pose diagnostic and management challenges due to their unusual presentations and sometimes inconclusive biochemical test results. It also highlights the need to consider advanced imaging early in cases of prolonged hypoglycemia, particularly when initial imaging studies are indeterminate.