Insomnia Symptoms, Subjective Appraisals, and Fatigue: A Multiple Mediation Model

Fatigue and insomnia are common debilitating symptoms associated with multiple sclerosis (MS). Negative subjective appraisals of symptoms may influence both insomnia and fatigue severity, but this relationship has not been examined among those with MS. The relationship between insomnia symptoms and both physical and cognitive fatigue were examined. Health-related self-efficacy, fatigue catastrophization, and rumination were examined as potential mediators of the relationship between insomnia symptoms and fatigue.Participants diagnosed with MS (N = 115) were recruited from hospital and community settings in a large metropolitan city.Participants completed self-report questionnaires, including: Modified Fatigue Impact, Insomnia Severity Index, MS Quality of Life Questionnaire-54, Fatigue Catastrophizing Scale, Multidimensional Health Locus of Control Scale, and the Rumination-Reflection Questionnaire. Two multiple mediation analyses were performed using bootstrapping techniques, examining the cognitive and physical domains of fatigue as separate outcomes.Mediation analyses revealed a significant association between insomnia symptom severity and the cognitive and physical domains of fatigue. Fatigue catastrophizing was the only significant mediator, accounting for 25% of the variance in the relationship between insomnia symptoms and the cognitive fatigue. However, fatigue catastrophizing did not significantly mediate the relationship between insomnia symptoms and physical fatigue, indicating physical and cognitive fatigue may reflect distinct processes in fatigue expression in those with MS.