IntroductionObjective algorithms (OA; Ramanujam, 2020) identify SPMS in those with clinically assigned (CA) RRMS, suggesting SPMS is under-diagnosed in practice. It’s unclear if clinicians are aware of this evolution and escalate therapy in response to clinical worsening with highly active (HA) disease modifying treatments (DMT).ObjectiveAssess whether treatment intensity escalates as the disease advances from RRMS to OA-SPMS and from RRMS to CA-SPMS.MethodsMS registries in Czech Republic, Denmark, Germany, Sweden and UK were used. Active DMTs at the date of last visit were classified as highly active (HA) or not, and DMT usage prior to CA-SPMS or OA-SPMS classification.Results3740 SPMS and 9542 OA-SPMS patients were on DMTs. HADMT use was 21.3% prior to OA-SPMS clas- sification in RRMS and 27.9% (p<0.0001) once classified. HADMT use was 23.5% prior to CA-SPMS diagnosis and 36.9% (p<0.0001) once diagnosed. HADMT use in the UK was lower than in other registries for all groups.ConclusionAcross Europe the evolution to clinical SPMS via OA-SPMS is eliciting a response from clini- cians that is not initially reflected in a change of diagnosis. Country variations in HADMT use in transitioning patients should be explored further.r.m.middleton@swansea.ac.uk74