(2.15) Insulinoma Masquerading as Seizures: A Diagnostic Conundrum

An insulinoma is a rare neuroendocrine tumor that is known for its potential to cause hyperinsulinemic hypoglycemia. This case presents the diagnostic challenges encountered in a patient initially diagnosed with idiopathic seizures, ultimately attributed to an undetected insulinoma causing profound hypoglycemic episodes.

Case(s) Description :

A 44-year-old woman presented to the emergency department (ED) after experiencing four days of unsteadiness, slurred speech, and weakness at home. The patient had been diagnosed with complex partial seizures a year prior. Despite receiving standard antiepileptic treatment, she had experienced multiple hospital admissions due to seizures over the past six months, leading to a decline in her overall health. Upon her arrival at the ED, the medical team observed hypoglycemia of 37 mg/dL, leading to repeated hypoglycemic episodes despite continuous dextrose administration. During a hypoglycemic episode, laboratory results indicated a low plasma glucose of 14 mg/dL, inappropriately elevated serum insulin of 18 μIU/mL (reference range 3 - 25 uIU/mL), proinsulin of 18.1 pmol/L (reference range 0.0-10.0 pmol/L), and C-peptide of 2.61 ng/mL (reference range 0.5 - 3.3). Additionally, the beta-hydroxybutyrate level was less than 0.50 mmol/L (reference range < 0.50 mmol/L) and serum sulfonylurea analysis was negative. These tests were suggestive of endogenous insulin production. Electroencephalogram (EEG), triple-phase spiral computed tomography (CT), magnetic resonance imaging (MRI), and transabdominal ultrasonography were unrevealing. Endocrinology recommended an endoscopic ultrasound (EUS), which identified a well-differentiated neuroendocrine tumor (NET) in the pancreatic body. The medical team initiated octreotide followed by an open distal pancreatectomy, confirming a 2.4 cm well-differentiated NET. The patient remained seizure-free during the 3-month follow-up.

Discussion :

The case portrays a patient who was treated for idiopathic, refractory epilepsy using anticonvulsants for a year before she was diagnosed with insulinoma-related hypoglycemia. Notably, it is critical to recognize that anticonvulsant therapies can further exacerbate hypoglycemia, potentially leading to severe and life-threatening episodes, as evidenced in this instance. This case highlights the significance of incorporating insulinoma and other potential causes of hypoglycemia into the differential diagnosis when evaluating seizures, particularly in scenarios where standard anticonvulsant therapies fail to yield seizure resolution. The diagnostic process encountered challenges as conventional noninvasive CT, MRI, and transabdominal ultrasonography could not identify the underlying cause. However, a pivotal turning point emerged with using EUS in diagnosing an insulinoma, shedding light on the previously elusive etiology of endogenous insulin production associated with the patient's condition. The case also underscores the significance of incorporating specialized imaging modalities like EUS when standard diagnostic tools prove inconclusive in resolving complex medical presentations.