Average MS relapse rate lower than in past decades: UK study

More effective DMTs might be the reason for the decline, researchers said

Marisa Wexler, MS avatar

by Marisa Wexler, MS |

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The average rate of relapses for multiple sclerosis (MS) in the modern era is lower than it has been in decades past, according to a new analysis from the U.K.

Scientists speculate the availability of new, more effective disease-modifying therapies may help explain why relapses appear to be less common now.

The study, “Real-world annualized relapse rates from contemporary multiple sclerosis clinics in the UK: a retrospective multicentre cohort study,” was published in Neurological Sciences.

Most people with MS have relapses, or flares — when symptoms suddenly worsen or new symptoms appear. While they usually ease after the relapse is over, patients often have lingering symptoms that persist even after the relapse resolves, making them a crucial driver of disease progression.

Clinical trials for experimental therapies will often examine a treatment’s effectiveness by reviewing its impact on the average number of relapses a year — called the annualized relapse rate (ARR). When these trials are designed, estimating the expected rate of relapses lets researchers calculate how many patients must participate to detect a statistically meaningful effect.

Relapses are hard to predict and they aren’t consistent across patients or over time. Studies have reported a trend toward a decrease in average relapse rates in the last decades.

This unpredictability makes clinical trials more complicated and can make it harder to ensure that appropriate care and resources get to the patients who most need them.

To better understand recent relapse rate trends, researchers reported on patients treated at several MS clinics in the U.K.

“The aim of this study was to estimate the real-world ARRs from contemporary MS clinics in the UK, in order to improve the feasibility estimations for clinical trials and facilitate MS service planning,” they wrote.

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Reviewing relapse rates, by the number

The researchers analyzed data on 8,783 patients at five clinics in England and Wales. Just over half (54%) had relapsing-remitting MS (RRMS), while 28% had secondary progressive disease (SPMS), 12% had primary progressive disease (PPMS), and 6% had clinically isolated syndrome (CIS).

Just over a quarter (27%) were being treated with a disease-modifying therapy. The researchers said this relatively low rate of patients on treatment may be partially attributable to the relatively strict therapy initiation guidelines in the U.K., which suggest that patients should have at least two clinically significant relapses in two years before starting first-line treatment.

During the three-month study period from April to June 2020, 113 patients had a documented relapse, making the total average ARR estimated to be at 0.05 relapses a year. This rate is lower than prior estimates and generally lower than those seen in clinical trials, which typically include patients with more active disease.

“The overall ARR of 0.05 is much lower compared to the ARRs reported in two previous UK studies 7-8 years ago,” the researchers wrote.

Among those with RRMS, the average ARR was 0.08 relapses a year. The average ARR was the same for the subset of RRMS patients on disease-modifying treatment. Among SPMS patients, the average ARR in the total group was 0.01 relapses per year, compared to 0.16 relapses a year for the subset on treatment.

The researchers said these data don’t account for the type of DMT or for other clinical differences. For example, those with a more aggressive disease are generally more likely to get disease-modifying treatment.

The data suggest the availability of new, more effective treatments could explain the lower ARRs in this study compared to years before, they said, noting more research is needed, given the data limitations.

“Further larger prospective studies are needed with real-world data, to improve the feasibility estimations of future clinical trials and facilitate MS service planning,” they said.

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