A 25-year-old man attends the Epilepsy Clinic. He has suffered tonic-clonic seizures for 7 years. After initial poor response, his epilepsy is now well-controlled on sodium valproate 1.5 g daily. He has been seizure-free for 3 years. His compliance with therapy is good.

From review of his case sheet, you note a family history of cerebrovascular disease with both grandparents suffering stroke.

At time of diagnosis, magnetic resonance imaging (MRI) brain showed no structural abnormality and interictal electroencephalogram (EEG) was unremarkable.

He is concerned over weight gain and hair loss that he attributes to his anticonvulsant therapy. He is considering stopping his sodium valproate.

What feature in his history predicts seizure recurrence upon discontinuation of therapy?