Secondary progressive MS (SPMS) is a research area that is attracting more attention as better treatment options are still needed for this patient group. The assignment of SPMS by clinicians can differ between countries and may be influenced by drug prescription guidelines, reimbursement issues and other societal limitations.
To compare the clinically assigned SPMS proportion to three objective SPMS classification methods in five MS registries.
Data from MS registries in the Czech Republic (CR) (11,336 patients), Denmark (10,255 patients), Germany (23,185 patients), Sweden (11,247 patients) and the United Kingdom (UK) (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 index period (1 January 2017 – 31 December 2019). In addition to clinically assigned SPMS three different classification methods were applied; method 1: modified real world EXPAND criteria (Kappos et al, Lancet 2018:391; 1263-1273), method 2: the data-derived definition from Melbourne University without the pyramidal Functional Systems Score (Lorscheider et al, Brain 2016:139; 2395-2405) and method 3: the decision tree classifier from Karolinska Institutet (Ramanujam, R. et al., 2020. medRxiv, 2020.07.09.20149674).
The SPMS proportions per registry, when comparing the clinically assigned SPMS with the results of the three classification methods, were CR: 8.8%, 21.3%, 22.1%, 25.0%; Denmark: 15.5%, 27.5%, 25.4%, 28.0%; Germany: 15.6%, 15.4%, 16.7%, 25.4%; Sweden: 23.7%, 20.8%, 23.2%, 24.6% and UK: 34.3%, 21.7%, 38.4%, 58.3% for clinical SPMS and methods 1, 2 and 3, respectively.
The proportion of clinically assigned SPMS patients varies between MS registries. When applying other classification methods, the SPMS proportion generally increases but remains variable between registries. As some of the classification methods have extensive requirements regarding data density, the number of unclassifiable samples created are considerable for some of the registries, which will influence the results. Providing a classification method that depends on objective information could prove useful when attempting to estimate the proportion of SPMS patients in MS populations but the choice of method may depend on the data characteristics of the individual MS registry.