The objective of the study is to assess dimethyl fumarate (DMF) adherence in individuals with multiple sclerosis (MS) who had received prior treatment and had no treatment before DMF.

Treatment adherence in MS is crucial for long-term effectiveness and patient outcomes. The reasons for non-adherence have been identified. However, there is limited data on people with a history of prior disease-modifying therapies (DMT) compared to treatment-naïve individuals.

A total of 497 individuals with MS who had been treated with DMF, and had at least 6 months of follow-up between Jan 1, 2013 and Dec 31, 2023 were retrospectively included. People with MS were categorized into two groups: those who had received prior treatment (therapy switch) before starting DMF (TS-DMF) and those who were treatment-naive before starting DMF (TN-DMF). Demographic, clinical, radiological, and laboratory data were collected before, at the start of, and after DMF treatment. 

The mean age was 37.5±11 with 38.6% being male. The mean disease duration was 8.4±6.9 years and EDSS score was calculated as 1.33±0.78. A total of 225 individuals in TS-DMF group and 272 individuals in TN-DMF group were compared. The final EDSS score was significantly lower in TN-DMF group (0.86±1.09) compared to TS-DMF group (1.37±1.62) (p<0.0014). People in TS-DMF group were more likely to discontinue treatment due to ineffectiveness than people in TN-DMF group (p<0.001). TN-DMF group exhibited higher rates of non-adherence with DMF compared to TS-DMF group (p<0.01).

Non-adherence in DMF treatment is particularly pronounced in patients who had not previously used DMTs. Contributing factors can include challenges in accepting a chronic disease, the burden of a daily medication use in a young age, and the impact of side effects. Enhancing clinical support throughout the treatment process, along with implementing patient-centered education programs, may help improve long-term adherence and overall treatment success.