Epileptic phenotype in late-onset hyperinsulinemic hypoglycemia successfully treated by diazoxide.

Objectives: Serious hyperinsulinemic hypoglycemia (HH) is generally the main initial symptom of hyperinsulinism. Epilepsy, without any overt feature of hypoglycemia, might be a very rare initial presentation of late-onset isolated hyperinsulinism.

Case Presentation: We describe a case of late-onset HH in a 15-year-old boy with a history of idiopathic generalized epilepsy, now named genetic generalized epilepsy (IGE/GGE), beginning with a tonic-clonic seizure at the age of 11 years. Subsequently, absences with rare eyelid myoclonia were recorded on electroencephalogram (EEG), followed by episodes of impaired consciousness with facial myoclonia. Neurological status was normal except attention-deficit hyperactivity disorder (ADHD). At the age of 15 years, an episode of slight alteration of consciousness with neurovegetative signs could be recorded, which did not correspond to an absence status. Hypoglycemia due to hyperinsulinism was documented (clinically, biologically, and genetically). Diazoxide treatment resolved the glycopenic symptoms, the non-hypoglycemic seizures and normalized brain electrical activity allowing complete withdrawal of antiepileptic medication.

Conclusions: Epilepsy can be a very rare initial feature of HH starting in childhood. The occurrence of atypical features in the context of GGE as "absence statuses" with unusual vegetative symptoms and facial myoclonia might be suggestive for HH. Careful assessment and specific treatment are necessary to prevent hyperinsulinism related brain damage. Our case showed that diazoxide might also resolve seizures and normalize EEG.