Purpose: To investigate the extent and causes of the differences in mortality found in studies on mortality in epilepsy based on a quantitative review of the literature.
Methods: We used MEDLINE database and Cumulative Index Medicus for 1960-2001, Excerpta Medica for 1948-1965, and relevant journals and bibliographies. We selected comparative studies investigating mortality in epilepsy patients conducted in the last 100 years. The Standardized Mortality Ratio (SMR) was selected as primary outcome. Nineteen studies were included. Pooled estimates were precision weighted and tested for homogeneity. Sources of variability between risk estimates were explored by using multivariate fixed-effects models.
Results: SMRs ranged from 1.3 to 9.3. Risk estimates proved heterogeneous (chi-square test statistic: 1,177; df = 18; p < 0.001). The most important determinant was "source population," explaining half of the variance of the estimates (R(2), 0.47; p = 0.006). SMRs in community studies ranged from 1.3 to 3.1, and for institutionalized populations, from 1.9 to 5.1.
Conclusions: Our results show that the mortality risk in patients with epilepsy is dependent on source population of patients. Within the different source populations, considerable unexplained variance remains. Hence no uniform summary estimate for the elevated mortality could be determined.