Unusual presentation of Lafora's disease.

Lafora's disease is a progressive myoclonus epilepsy with onset in adolescence and a gradual decline in cognitive functions and increase in seizure intractability. We present the case of a 16-year-old with precipitous dementia within 6 months of onset. Peripheral biopsies and EPM2A mutation analysis were negative. The diagnosis could be established only by brain biopsy.