Differences in correlates of fatigue between relapsing and progressive forms of multiple sclerosis.

Background: Fatigue is one of the most prevalent and impactful symptoms for people with multiple sclerosis (MS). Yet, fatigue is less understood in progressive forms of MS, and few studies have explored the extent to which MS disease course is associated with fatigue. The current study aimed to (1) describe fatigue severity and fatigue interference (the extent to which fatigue interferes with individuals' physical, mental, and social activities) in people with progressive MS (primary progressive MS and secondary progressive MS); (2) compare fatigue severity and fatigue interference in people with progressive forms of MS to people with relapsing-remitting MS (RRMS); and (3) identify factors associated with fatigue severity and fatigue interference in people with progressive forms of MS and RRMS.

Methods: Secondary analysis of baseline data from participants with MS (N = 573; progressive forms of MS n = 142; RRMS n = 431) in a survey-based longitudinal study on healthy aging in people with a physical disability. Primary outcomes were average fatigue severity (0-10 Numerical Rating Scale), and fatigue interference (PROMIS Fatigue Short Form). Correlates were variables across the demographic and biopsychosocial domains, collected with validated self-reported measures. Statistical methods included t-test and chi-square analyses to compare fatigue severity and fatigue interference in people with progressive MS to those with RRMS, and multiple regression analyses to examine the association of variables with fatigue severity and fatigue interference.

Results: Participants with progressive forms of MS reported moderate to severe levels of average fatigue severity (5.9 ± 2.8) and elevated levels of fatigue interference (T-Score of 58.2 ± 7.9). There were no group differences between people with progressive MS and RRMS in average fatigue severity or fatigue interference. Common factors associated with greater fatigue severity were lower income, being unemployed, shorter disease duration, greater disability, and greater sleep disturbance. Common factors associated with fatigue interference were younger age, lower income, being unemployed, greater disability, lower alcohol consumption, being a smoker, and greater sleep disturbance. For those with progressive forms of MS, longer MS disease duration was associated with lower average fatigue severity (b = -0.08, t(532) = -3.69, p < .001) and having a college degree or higher was associated with higher fatigue interference (b = 2.84, t(520) = 2.23, p = .026).

Conclusion: In this sample, fatigue severity and fatigue interference were similar for progressive forms of MS and RRMS. Future research should consider if interventions that work for fatigue management in people with relapsing forms of MS work similarly for people with progressive forms of MS.