Long-Term Disease Stability Assessed by the Expanded Disability Status Scale in Patients Treated with Cladribine Tablets in the CLARITY and CLARITY Extension Studies

Abstract

Treatment with cladribine tablets 10mg (cumulative dose 3.5mg/kg [CT3.5] over 2 years) in CLARITY and CLARITY Extension reduced relapse rate and slowed disability progression versus placebo in patients with relapsing remitting multiple sclerosis (RRMS). This post hoc analysis evaluated long-term disease stability assessed by the Expanded Disability Status Scale (EDSS) after treatment with CT3.5 in patients with RRMS in CLARITY and CLARITY Extension. Patients randomised to CT3.5 in CLARITY and placebo in CLARITY Extension, with ≥1 post-baseline EDSS measurement, were included (CP3.5; n=98). EDSS score over-time (from CLARITY randomisation to end of follow-up in CLARITY Extension, including the bridging interval between studies) was assessed at 6-monthly intervals, and separately time to 3- and 6-month confirmed EDSS score progression from CLARITY baseline. EDSS score worsening/improvement in each year was defined as any increase/decrease in minimum EDSS score at 6-monthly intervals; all other cases were classified as stable. Increase or decrease was defined as an EDSS score change of 1, 1.5 or 0.5 points at baseline EDSS ≤4.5, 0, ≥5.0 respectively. Five years post-CLARITY baseline, median EDSS remained stable versus baseline. Median EDSS score (95% confidence interval [CI]) for CP3.5 patients was 2.5(2.0-3.5) versus 3.0(2.5-3.5) at baseline. In each 12-month period, percentage of patients with EDSS score stability was >50%; improvement, 21-30%; worsening, 0-25%. During Year 5, percentage of patients with EDSS stability was 53.9%; improvement, 21.3%; worsening, 24.7%. Less than 30% of patients reached 3- or 6-month confirmed EDSS progression by Year 5. EDSS score was stable up to 5 years post-CLARITY baseline for the CP3.5 group. Between 20-30% of patients demonstrated improvement in EDSS score versus baseline each year.