Fatigue is one of the most common and debilitating symptoms of multiple sclerosis (MS) but is challenging to assess and has not been comprehensively characterized in patients with progressive MS.

In this study, patients with progressive MS (primary and secondary progressive MS, PPMS and SPMS) identified key concepts of both physical and mental fatigue and characterized them differently; most participants reported daily fatigue lasting several hours a day and impacting their health-related quality of life.

Based on these findings, the Fatigue Severity Impact Questionnaire—Relapsing Multiple Sclerosis (FSIQ-RMS) is potentially suitable for assessing MS-related fatigue in progressive MS (PPMS and SPMS); however, additional research is needed to validate the FSIQ-RMS in this population.

In the future, patient-reported outcome instruments that assess fatigue in progressive MS should separate physical and mental aspects of fatigue and include key concepts reported in this study.