Establishing an early diagnosis of Lafora disease (LD) is often challenging. We describe two cases of LD presenting as myoclonus and tonic–clonic seizures, initially suggesting idiopathic generalized epilepsy. The subsequent course of the disease was characterized by drug-resistant myoclonic epilepsy, cognitive decline, and visual symptoms, which oriented the diagnosis toward progressive myoclonic epilepsy and, more specifically, LD. Early in the evolution in the first case, and before histopathologic and genetic confirmation of LD in both cases, Fluorodeoxyglucose positron emission tomography (FDG-PET) revealed posterior hypometabolism, consistent with the well-known posterior impairment in this disease. This suggests that FDG-PET could help to differentiate LD in early stages from other progressive myoclonic epilepsies, but confirmation is required by a longitudinal study of FDG-PET in progressive myoclonic epilepsy.