Can mortality data be used to estimate amyotrophic lateral sclerosis incidence?

Background: Because studies of the incidence of amyotrophic lateral sclerosis (ALS) have uncertain feasibility and high costs, mortality rates are often used to provide an estimate. We performed a systematic review of the literature concerning mortality related to ALS. We aimed to use well-known criteria of good epidemiological practice to assess the methodological quality of the studies.

Methods: A Medline and ScienceDirect literature search was performed to identify studies on ALS mortality published from 1971 to 2009. The literature was examined following 6 criteria.

Results: Of the 29 studies examined, almost all presented a clear definition of the population at risk, but 55% of the papers did not report on the accuracy of death certificates, and the use of both 'underlying' and 'contributory' causes of death was identified in only 41% of cases. When comparing ALS mortality data between calendar dates, the codes from the International Classification of Diseases were consistent overall, except in 3 studies. A majority of articles that compared mortality patterns between geographical regions or ethnic groups discussed the key issues of comparability of health care and equality of access. Overall, among the 29 ALS mortality studies, only 3 complied with all the criteria. In 2 of them, the mortality rates were highly consistent with available incidence data.

Conclusion: Only few studies on mortality data followed a high-quality methodology. When studies complied with the criteria, they showed good accuracy with regard to incidence rates. The criteria used in this study could also be used to guide future studies based on mortality data.