Prevalence and associated features of epilepsy in adults with Down's syndrome.

The aim of this study was to establish the prevalence of epilepsy in persons with Down's syndrome aged 19 years and over. A total of 191 adults with Down's syndrome were identified, giving a prevalence of 0.76/1000 (95% CI 0.75 to 0.77). Of these, 18 had epilepsy, giving a prevalence of 9.4% (95% CI 5.3% to 13.5%). The prevalence of epilepsy increased with age, reaching 46% in those over 50. The neurophysiological (EEG) findings of the epilepsy group were compared with those of a control group of Down's syndrome adults without epilepsy. Paroxysmal abnormalities consistent with a diagnosis of epilepsy were found in 80% of the epilepsy group, compared with only 13% of controls (P < 0.001). Epilepsy of late onset was associated with diffuse EEG abnormalities and clinical evidence of dementia. The age distribution and EEG findings suggest two independent processes in the causation of epilepsy: late-onset epilepsy associated with clinical evidence of dementia, and early-onset epilepsy in the absence of dementia.