This phase 4 retrospective chart abstract study included data from 5 US centers (April 2017–March 2018) and from the MSBase registry (November 2018). Key inclusion: DMF treatment for 3–24 months per standard of care and discontinued DMF; baseline absolute lymphocyte count (ALC) >0.91x10⁹/L, with ≥2 ALC <0.91x10⁹/L on-treatment, and ≥2 ALC post-DMF, 1 of which was recorded ≥90 days post-DMF. Primary endpoint: change in ALC measurements over time.

Thirty-three patients met the inclusion criteria (US, 27; MSBase, 6); mean (range) age 51.4 (20-75); median (range) baseline ALC 1.6 (1.0-3.9) x10⁹/L. Patients were treated with DMF for a median (range) 17.8 (4.8–23.9) months. Patients developed lymphopenia (first ALC <0.91x10⁹/L) 5.3 months (median) after initiating DMF. Median (range) ALC at discontinuation was 0.5 (0.2–1.0). The median ALC was 0.8x10⁹/L >3 months after DMF discontinuation. Of patients with ≥1 ALC <0.8x10⁹/L on treatment (n=32), the majority (78%) had ≥1 ALC ≥0.8x10⁹/L post treatment; median time: 4.1 months after discontinuation. ALC >0.8x10⁹/L was generally identified as when physicians reinitiated DMF or another DMT.

These data suggest that among a majority of patients that experience lymphopenia during DMF treatment, meaningful lymphocyte reconstitution occurs after 3 months of treatment discontinuation. However, lymphocyte reconstitution is influenced by visit schedule, and may be evident earlier in patients with more frequent assessments. These lymphocyte reconstitution dynamics data may be informative for clinicians when managing patients who develop lymphopenia during DMF treatment.

Study Supported by: Biogen