Insulinoma diagnosed as drug-refractory epilepsy in an adolescent boy: a case report

Solitary insulinoma is a rare pancreatic tumor in all age groups with an estimated incidence of 1 in 250 000 persons a year. It is even rarely in childhood and mostly shows benign behavior. Cases with uncertain or malignant biology are extremely rare with less than 30 cases described in the literature. Here we report a case of pediatric insulinoma, the first in our department files in the past 20 years, with rapid clinical course following a clinical misdiagnosis as juvenile myoclonic epilepsy, which was complicated with low glucose level (20 mg/dL) and neuroglycopenia. Our case underlines some unusual features of a pediatric insulinomas presented without past medical and family history, after surgery complicated with mental retardation and recurrent epileptiform episodes. Despite the small tumor size, low Ki67 index/mitotic rate and benign immunophenotype marked by positivity for pro-insulin but negativity for β-HCG, the diagnosis was concluded as insulinoma of uncertain biological behavior due to vascular tumor invasion in agreement with the 2003 WHO Classification for Pancreatic Endocrine Neoplasms. Besides these features, perineural invasion can differentiate insulinomas of uncertain outcome from benign insulin producing tumors. Pediatric insulinomas may present misleading symptoms of epilepsy in neglected cases coming from poor socioeconomic background. Chronic insufficient blood glucose level might contribute to mental retardation and epilepsiform myoconvulsions to be prevented. Differentiation between insulinoma with benign and uncertain behavior is difficult where histological pattern and tumor immunophenotype are less important than the critical morphological parameters. Life long follow-up including regular control of blood glucose and abdominal status of patients are essential for proper assessment of clinical outcome of pediatric insulinoma.