OBJECTIVES: Fatigue is a common and disabling symptom experienced by relapsing multiple sclerosis (RMS) patients. The Fatigue Symptoms and Impacts Questionnaire – Relapsing Multiple Sclerosis (FSIQ-RMS) assesses its impact on quality of life from a patient perspective. This study aimed to identify the factors impacting FSIQ-RMS scores over time in RMS patients from the US.

METHODS: In this online prospective study, US RMS patients aged 18-55y and with a Patient Determined Disease Steps (PDDS) score ≤5 were invited to complete a baseline 7-day FSIQ-RMS symptom diary (daily recall). Socio-demographic and medical characteristics were also collected. Follow-up FSIQ-RMS were collected at 6, 12, and 18 months. Patients with at least two complete FSIQ-RMS measurements (n=160) were included in a longitudinal analysis using a multivariate linear mixed model to identify risk factors for a higher FSIQ-RMS score (fatigue-related symptom component). Risk factors were identified based on their univariate association with the FSIQ-RMS score followed by a backward selection procedure, keeping only those significantly and independently associated with the FSIQ-RMS score.

RESULTS: Fatigue-related symptom scores were higher in patients with a baseline PDDS score >3 (p-value=0.005), with at least one fatigue-impacting factor (p-value=0.003 and 0.005 for one and for ≥1 factors, respectively), who received fatigue treatment(s) (p=0.01 for at least one received treatment, p-value=0.007 if always under treatment), and with a history of anxiety/depression (p-value=0.009) and pain (p-value=0.02). However, no time effect was observed.

CONCLUSIONS: These results suggest that baseline PDDS levels, fatigue-impacting factors, exposure to fatigue treatment, and history of anxiety/depression or pain may all impact FSIQ-RMS scores over time in this cohort of US RMS patients, with no significant time effect over an 18-month follow-up period. This provides new insights into patients’ perspective on the impact of fatigue-related symptoms and supports the integration of patient-reported instruments into clinical practice.