The prevalence of vegetative and minimally conscious states: A systematic review and methodological appraisal

OBJECTIVES: To systematically review prevalence studies of vegetative state (VS) and minimally conscious state (MCS) in geographically defined populations, to appraise study methods and assess sources of heterogeneity. METHODS: MEDLINE, EBM Reviews, and EMBASE databases were searched using key terms. Two reviewers independently identified pertinent articles and screened the references for additional studies. Studies measuring the prevalence of VS and/or MCS in a defined population were included, and information on characteristics, methods, and results was extracted. Heterogeneity was quantified through the statistic I. RESULTS: We identified 5 cross-sectional prevalence surveys of VS and 1 of MCS. Prevalence ranged from 0.2 cases per 100,000 inhabitants to 3.4 for VS and was 1.5 per 100,000 for MCS. Relevant heterogeneity (I = 99.0%) prevented us from calculating a summary estimate. The prevalence of trauma cases varied from 21.9% to 53.8%. Variability pertaining to diagnostic criteria, definition of case, and methods of ascertainment was found. CONCLUSION: In the few prevalence studies of VS and MCS that were identified, the estimates showed high variability and could not be pooled. Future studies should consider using comparable methods for the definition, ascertainment, and confirmation of cases.