Until recently, disease modifying treatment options for MS patients with a secondary progressive course (SPMS) were limited, leading to the common practice of off-label treatment with drugs approved for relapsing-remitting MS. We previously showed that applying objective algorithms tend to increase the proportion of SPMS in MS registries, suggesting that SPMS is under-diagnosed in clinical practice, possibly related to available treatment options.
To compare characteristics of patients clinically assigned an RRMS course that are re-classified when an algorithm-based SPMS assignment method is applied.
Data from MS registries in the Czech Republic (11,336 patients), Denmark (10,255 patients), Germany (23,185 patients), Sweden (11,247 patients) and the United Kingdom (5,086 patients) were used. Inclusion criteria were patients with relapsing remitting (RR)MS or SPMS with age ≥ 18 years at the beginning of the study period (1 January 2017 – 31 December 2019). In addition to clinically assigned SPMS a data-driven assignment method was applied in the form of a decision tree classifier based on age and last EDSS (Ramanujam, R. et al., 2020. medRxiv, 2020.07.09.20149674).
Across the five registries 8,372 RRMS patients were re-assigned as SPMS (Denmark: n=1,566, Czech Republic: n=1,958, Germany: n=2,906, Sweden: n=648, United Kingdom: n=1,294) increasing the overall SPMS proportion from 17% to 31%. Re-assigned patients tended be younger, were older at onset and had experienced a quicker progression to SPMS. The overall proportion of clinically assigned SPMS patients on disease modifying treatments (DMTs) was 36% but varied greatly between registries (Czech Republic: 18%, Denmark: 35%, Germany: 50%, Sweden: 40%, and the United Kingdom: 12%) whereas a higher proportion of 69% (OR=4.0, P<0.00004) were on DMTs among RRMS patients re-assigned as SPMS (Czech Republic: 71%, Denmark: 68%, Germany: 78%, Sweden: 80%, and the United Kingdom 40%).
SPMS patients on DMTs may be clinically mis-classified as RRMS, most likely by not being re-assigned to SPMS after conversion has occurred. This challenges the use of time to SPMS conversion as an outcome in comparative effectiveness studies using real world evidence data and argues for the use of objective classification tools in the analysis of MS patient populations.