Influence of epilepsy on mortality in mental retardation: an epidemiologic study.
A cohort consisting of all persons with known mental retardation (MR) and living in a Swedish province on December 31, 1985, was followed for 7 years (1987-1992) to study the mortality pattern. A file of the cohort was linked to the cause-of-death pattern of the general population in the study area. One hundred twenty-four deaths (8.4%) occurred among the 1,478 persons with MR. Thirty deaths (10.1%) occurred among the 296 persons with epilepsy and MR. The standardized mortality ratio (SMR) in those with only MR was significantly increased as compared with that of the general population: 1.6 [95% confidence interval (CI) 1.3-2.0]; MR and epilepsy, 5.0 (CI 3.3-7.5); and MR, epilepsy, and cerebral palsy (CP), 5.8 (CI 3.4-9.7). Mortality was increased both in patients with partial seizures without seizures secondarily generalized (SMR 3.7, CI 1.0-13.6) and in patients with seizures secondarily generalized (5.0, CI 2.3-11.0). The highest mortality occurred in patients who had seizures that were always generalized from the onset: 8.1 (CI 5.7-11.5). Mortality increased with increasing seizure frequency during the year preceding the prevalence date. In patients with epilepsy and MR, pneumonia was the most common cause of death and a seizure was the probable cause of death in 6.7%. Epilepsy is associated with a significantly increased mortality in persons with MR. The increase is related to seizure type and seizure frequency. Death in persons with epilepsy and MR is seldom directly due to seizures. Other impairments associated with epilepsy and MR are important causes of death.