Annualized relapse rates for a contemporary multiple sclerosis clinic in the UK: a retrospective cohort study

Introduction: Annualized relapse rate (ARR) is routinely used as the primary outcome measure in MS clinical trials and is important in service planning. Most disease modifying therapies (DMTs) are prescribed in people with relapsing remitting MS (RRMS) and the ARR of secondary progressive MS (SPMS) and RRMS has not been accurately described in a modern clinical cohort. Recent treatment advances have led to more people with MS being effectively managed with early intensive medications, reducing the frequency of reported relapse rates in RRMS. Aims: To facilitate MS service planning and improve the feasibility estimations for clinical trials in MS. Objectives: To establish a current estimated ARR observed in a contemporary MS clinic in the UK. Methods: A retrospective cohort study examined all relapses recorded in a university hospital serving the local MS population. A random sample of 812 MS Nottingham patients from our database were reviewed for reported relapses from April 1 to June 30, 2020 and the same period in 2019, to account for potential reporting bias during the COVID-19 pandemic. The MS clinical database, nurse and admin registries, medical and telephone records for those individuals were reviewed at the end of 2020 for possible relapses during the study periods. Results: Among MS patients followed up in clinic, 60% had RRMS, 23% SPMS, 14% PPMS and 4% CIS. We identified 30 clinician confirmed relapses during the study period equating to an ARR of 0.15 for all MS patients treated and untreated. 70% of RRMS and 18% of SPMS were on DMTs. The ARR in RRMS and SPMS were the same (0.15). Validating this with pre-pandemic 2019 records found similar results. Conclusions: This contemporary UK-based study reports halving of the ARR previously reported in 2 similar studies in the UK 8 years ago. While relapse prevention has been achieved in RRMS, there appears to be significant unappreciated relapses occurring in the SPMS (pre-siponimod) cohort.