The risk of converting to secondary-progressive multiple sclerosis (SPMS) has declined in recent years for patients who have an earlier disease onset, an analysis of data from the Swedish MS Registry indicates.
The conversion is also occurring later in life and in people who have lived with multiple sclerosis (MS) longer, with the greatest change seen in those who were younger at the onset of disease, analyses indicated.
“Improved disease modification [is] likely to contribute to postponing the conversion to SPMS supporting the long-term benefits of DMTs [disease-modifying therapies],” Elena Flavia Mouresan, PhD, said in an oral presentation at the European Committee for Treatment and Research in Multiple Sclerosis (ECTRIMS) and the Americas Committee for Treatment and Research in Multiple Sclerosis (ACTRIMS) meeting, held this month in Milan, Italy and online.
“These results highlight the importance of early DMT and the importance of strategies to earlier diagnosis,” Mouresan, a research specialist at the Karolinska Institute in Sweden, said in “A decreasing risk of secondary progressive multiple sclerosis in Sweden 2005-2020.”
About 85% of MS patients are first diagnosed with relapsing-remitting MS (RRMS), which is characterized by periods of symptom worsening interspersed with periods of remission where symptoms ease and remain stable. Over time, some patients will transition to a SPMS disease course, where symptoms continue to accumulate gradually even in the absence of relapses.
Left untreated, it’s believed that about half of RRMS patients would transition to SPMS within a decade of being diagnosed. However, fewer RRMS patients now transition due to the increasing availability of DMTs. This transition seems to occur later in the course of the disease.
Declining EDSS scores
The Swedish MS Registry, officially launched in 2000, houses long-term clinical and demographic information from more than 22,000 Swedish MS patients, about 84% of all MS patients in the country.
In last year’s annual report from the Registry, scientists noticed the average Expanded Disability Status Scale (EDSS) score for the registry population has decreased in the last two decades, suggesting generally lower disability in recent years. The average EDSS score in 1998 was 4.2; in 2022, it was 2.7.
“We suspect that this is due to a decrease in the proportion of secondary progressive patients in the registry, because when we looked at the average EDSS scores of the relapsing-remitting patients and secondary progressive patients separately, we did not observe this trend,” said Mouresan, who reviewed with her colleagues the incidence rate of SPMS within the registry each year between 2005-2020, covering nearly 20,000 MS patients, about 88% of all its participants.
The proportion of participants with SPMS declined from 23.3% in 2005 to 21.9% in 2020, results showed, “with the majority of the decline happening in the last five years,” Mouresan noted.
Statistical analyses showed a 2% decrease in the SPMS proportion per calendar year after adjusting for potential factors such as sex and age.
Incidence rate of SPMS falling
Likewise, the incidence rate of SPMS — or the number of new cases per year — declined significantly from 2.7 cases per 100 person-years (PY) in 2005 to 0.9 cases per 100 PY in 2020, a significant decrease of 7% per calendar year in final statistical analyses. PY is a measure that accounts for total years of observation time across all patients.
Researchers also noticed differences over the years in the age and disease duration at the time patients transitioned to SPMS. Within those 15 years, the median age at converting to SPMS increased from 58 to 64, and the median disease duration at conversion increased from 24 to 30 years. That amounts to about a four-month increase in median age and median disease duration at SPMS conversion per calendar year.
Finally, the average age at MS onset among those who eventually converted to SPMS increased from 34 in 2005 to 38.5 in 2020. This shift wasn’t seen among RRMS patients who didn’t convert to SPMS, “where the age at onset has remained stable all the years,” Mouresan said.
Overall, “the risk for patients with RRMS to convert to SPMS has decreased significantly in Sweden since 2005 and conversion now occurs later in life and a longer time after onset,” the researcher said, noting the greatest change is seen in those with an earlier onset of MS.
The findings are limited by changes in registry coverage over time, Mouresan said. For example, more severe cases were more likely to be captured in earlier years than mild ones and older patients were also underrepresented.
Other factors related to disease progression also were not accounted for in the analysis, but might “contribute to the postponement of SPMS conversion,” the researcher said. These may include better lifestyle choices, such as not smoking, advanced treatment of coexisting conditions, and greater general health among registry participants.
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