Characterizing Fatigue by Multiple Sclerosis Subtype and Determining Validity of a Fatigue Scale Specific to Persons With Progressive Multiple Sclerosis.

Background: Fatigue is a common and debilitating symptom of multiple sclerosis (MS). Prior work suggests that the prevalence of fatigue is higher in progressive MS (PMS) than relapsing MS (RRMS). No patient-reported outcomes of fatigue have been validated specifically for individuals with PMS, despite evidence that they characterize fatigue differently than individuals with RRMS. Therefore, the objective of this study was to characterize fatigue in both the RRMS and PMS subtypes and determine the convergent validity of the Fatigue Symptoms and Impacts Questionnaire (FSIQ) for individuals with PMS.

Methods: A nationwide survey yielded 806 (637 RRMS, 169 PMS) complete responses. The survey collected demographic information and self-reported disease severity, as well as measures of fatigue, health-related quality of life, and self-reported functioning.

Results: People with PMS reported significantly more severe fatigue than those with RRMS (P < .001). The FSIQ subdomains of physical, cognitive/emotional, and coping demonstrated moderate (r = 0.5-0.75) to excellent (r > 0.75) validity (P < .001) with other measures of fatigue.

Conclusions: More severe fatigue in people with PMS as compared to those with RRMS underscores the importance of using validated tools to capture fatigue in persons with PMS. The FSIQ is a valid and freely available tool to capture the physical, mental, and emotional fatigue of individuals with PMS.