Prognosis of amyotrophic lateral sclerosis and the effect of referral selection.

We followed two cohorts of Amyotrophic Lateral Sclerosis (ALS) patients to examine the survival and prognostic factors of ALS and the impact of selective referral on prognosis of ALS. The first cohort consisted of population-based incident ALS cases from Harris County, Texas, first diagnosed between 1985 and 1988. The second was a clinical series from a tertiary care center in Houston, Texas, diagnosed between 1977 and 1989. The overall 3-year survival was 29% in the incidence cohort and 32% in the referral cohort; however, the 5-year survival was much lower for the incidence cohort than the referral cohort (4% vs 21%). The large difference in 5-year survival was not explained by the distributions of prognostic factors in the two cohorts but due to stronger unfavorable effects of prognostic factors in the incidence cohort than the referral cohort. In both cohorts, older age at diagnosis, bulbar onset, and positive family history of ALS were unfavorable prognostic factors while blacks had better survival than whites or hispanics. We confirmed that longer duration from onset to diagnosis was a favorable prognostic factor in both cohorts but the effect was more pronounced in the referral series.