- Studies of long-term disability in people living with primary progressive MS have demonstrated that there are distinct trajectories or pathways of disability accumulation.
- In contrast, studies in people living with secondary progressive MS have yielded inconsistent results on the accumulation of long-term disability.
- Using an international network of MS registries and databases, researchers have identified subgroups of people with secondary progressive MS with similar pathways of disability over time.
What is known about disability progression pathways in people with progressive MS?
The transition to secondary progressive MS from relapsing remitting MS can be hard to detect and is generally recognised after the fact. Attempts have been made to clearly define the transition to secondary progressive MS, but ultimately, the exact determination of a time point of transition is unlikely.
In primary progressive MS and secondary progressive MS, the rate of disability accumulation has been found to be equal in some studies. However, other research has found that in primary progressive MS, the process of disability progression takes longer.
Research has also revealed the factors linked to the accumulation of disability in secondary progressive MS are varied, and some of the research is inconsistent.
In a previous study, researchers identified different progression trajectories in people living with primary progressive MS. However, this is yet to be determined in people with secondary progressive MS.
What did the researchers do?
Using the BigMSData Network, an international network of MS registries and databases from Italy, France, and Sweden, as well as MSBase (one of the world’s largest clinical databases), researchers aimed to identify the different trajectories of disability progression in people with secondary progressive MS, as measured by the Expanded Disability Status Scale (EDSS).
Published in the Journal of Neurology, Neurosurgery, and Psychiatry and led by Professors Tomas Kalincik and Helmut Butzkueven, the study identified two cohorts of people from these registries who had a secondary progressive MS diagnosis from a clinician (cohort 1) or satisfied objective criteria to have secondary progressive MS (cohort 2).
People in these cohorts had a baseline EDSS score of 3-4, meaning they could walk unaided but with moderate disability in a functional system. A total of 3,613 people were included in cohort 1 and 7,613 people in cohort 2.
What did the study find?
Using the BigMSData Network and EDSS scores, the researchers modelled disability progression pathways in both cohorts to an EDSS of 6, the point at which a walking aid is required.
In cohort 1, they identified three distinct disability progression trajectories, which they named:
- Mild class (35.9% of people) – average time to an EDSS of 6 was 12.1 years, reached at an average age of 66.5 years.
- Moderate class (53.6% of people) – average time to an EDSS of 6 was 5 years, reached at an average age of 53.1 years.
- Severe class (10.5% of people) – average time to an EDSS of 6 was 1.7 years, reached at an average age of 44.9 years.
When the researchers compared the characteristics of the three groups at the start of the study, the severe class showed a younger age and shorter disease duration. In this class, there was a higher frequency of people who experienced one relapse in the previous two years, and people with at least one relapse during the follow-up period.
A similar trend was also observed in cohort 2. However, more people were classified as severe in this cohort (10.5% in cohort 1 vs. 27.7% in cohort 2).
The researchers next investigated baseline characteristics on class severity. What they found was:
- Longer disease duration was linked with a lower chance of being in the moderate or severe class.
- People who experienced at least one relapse in the previous two years showed a high chance of being in the moderate class, but not severe class.
What is the take-home message from this study?
The results of this study highlight three progression trajectories of people with secondary progressive MS. Identifying these classes may help design clinical trials in secondary progressive MS.
For example, selecting participants at higher risk of disability progression over the typical 2–3 years of follow-up may increase the power of the clinical trial since more disability events are expected. This may lead to more rapid ways of identifying successful treatments.
Furthermore, there may be biological differences between these progression trajectories, such as MRI profiles, blood profiles or other biomarkers. Research into these may help differentiate between these secondary progressive MS classes.
