Preventable and unpreventable causes of childhood-onset epilepsy plus mental retardation

OBJECTIVE. The objective of this study was to determine the causes of childhood epilepsy associated with mental retardation and determine whether these causes are preventable. METHODS. We selected all patients from the Nova Scotia population-based childhood epilepsy cohort (n = 692) who had mental retardation and had epilepsy onset between 1977 and 1985. Causes and family history were determined by chart review and caregiver interview after 18.8 (SD:+/- 7) years of follow-up. RESULTS. Overall, 147 patients had mental retardation and epilepsy (21% of all childhood epilepsy). Standard psychological testing was available for 57%; 38.5% were too impaired for testing, which left 4% with the degree of mental retardation assessed clinically. Severe/profound mental retardation predominated ( mild: 24%; moderate: 23%, severe/profound: 53%). Fifty-nine percent had additional severe neurologic deficits, most often associated with severe mental retardation. Epilepsy syndromes were symptomatic generalized (n = 73), partial ( n = 58), and other (n = 16). Most had a brain imaging study: 91% had a computed tomography scan, and 12% had an MRI scan. Sixty-three percent had a defined cause; 37% had an unknown cause. A defined cause was more likely in those with severe mental retardation ( 60 of 78 vs 31 of 65). Identified causes were prenatal or genetic (65%), perinatal (8%), or complications of prematurity (13%). Only 11 (7%) had an acquired cause that was potentially preventable. Many (36%) had a first- or second-degree relative with epilepsy, more often in those without a clear cause (54% vs 30%) and without additional neurologic disability ( 57% vs 26%). CONCLUSIONS. Approximately 20% of children with epilepsy have mental retardation. The cause is prenatal or genetic in nearly two thirds, and only 7% have an acquired, preventable cause. Important genetic influences may be present, especially in the absence of a defined cause.