Trend toward milder disability
The investigators next examined whether the rate of accumulation of disability among patients with MS had changed from year to year since DMTs were introduced. They conducted a univariate analysis of MSSS for 6,238 patients who were enrolled in the N.Y. State during 1996-2007. They found that patients who were enrolled in more recent years had significantly lower MSSS than patients who were enrolled in earlier years, regardless of disease duration. When Dr. Kister and colleagues replicated their analysis using EDSS, they found significantly lower levels of disability for patients enrolled in more recent years, except for patients with disease duration of 26-30 years. A multivariate analysis showed that the median MSSS of enrollees into the N.Y. State MS Consortium decreased from 5.04 in 1996 to 3.78 in 2006.
In a subsequent study, Dr. Kister and colleagues examined the age at which patients in the MSBase registry reached various disability milestones (e.g., EDSS of 6, which indicates the need of a cane to walk outdoors), according to their year of enrollment in the registry. They found a significant increase in age at milestone achievement with each subsequent calendar year. For example, for every consecutive year of enrollment, the age at which patients attained an EDSS of 6 increased by 0.38 years. These analyses were confirmed for the subgroups of patients diagnosed according to the and criteria. The increase in age “is probably not just related to the shift in diagnostic criteria,” said Dr. Kister. When the researchers calculated the net average gains in years over the 13-year follow-up period, they found that patients who entered at the end of the enrollment period were 4.9 years older when they reached an EDSS of 6, compared with patients with an EDSS of 6 who entered at the beginning of the enrollment period.
International data show similar trends
Research conducted around the world shows similar trends, said Dr. Kister. In 2009, Veugelers et al. published the results of a study that included 1,752 patients with MS in Nova Scotia. Before the 1998 introduction of a drug insurance program that provides DMTs, the time to an EDSS of 6 was 14.4 years. After the introduction of this program, the time to EDSS of 6 was 18.6 years.
More recently, Capra et al. examined 1,324 patients with MS who attended an MS center in Brescia, Italy, during 1980-2010. They found that the age at which 50% of patients reached an EDSS of 6 was approximately 55 years in 1990. By 2010, the age at achieving this milestone had increased to approximately 63 years.
In a prospective study, Cree et al. examined the evolution of disability in 448 actively treated patients with relapsing-remitting MS and 69 patients with progressive MS. Approximately 45% of patients had no disability worsening during a 10-year follow-up period. Furthermore, a comparatively low 11% of patients had reached an EDSS of 6 at 10 years. The average disease duration of the cohort at that time was 17 years, said Dr. Kister. The results indicated that about 50% of patients would be expected to reach an EDSS of 6 after a disease duration of approximately 38 years, “which is much longer than in the natural history studies,” he added.
In 2019, Beiki et al. found that among patients with relapsing-remitting MS, the risk of reaching an EDSS of 6 decreased by 7% with each subsequent calendar year of diagnosis. The researchers did not observe a similar trend among patients with progressive MS. Their population-based, retrospective study included 7,331 patients in Sweden.
Two additional studies in Scandinavian populations add to the evidence of decreasing disability. In their examination of Swedish patients with MS who received a diagnosis of MS during 1968-2012, Burkill et al. found that the risk of death decreased over time. The hazard ratio of mortality for patients with MS, compared with a non-MS comparator group, decreased from 6.52 among those diagnosed during 1968-1980 to 2.08 for patients diagnosed during 2001-2012. The decrease in the risk of mortality was greater among patients with MS than in a matched comparator population. Similarly, in a nationwide, population-based study, Koch-Henriksen et al. found that all-cause excess mortality in Danish patients with MS decreased from 1950 through 1999.