Effects of pain on depression are mediated by fatigue, anxiety, and sleep in Multiple Sclerosis

Introduction: Relationships between pain and psychological functioning in Multiple Sclerosis have not been well studied. We examined whether fatigue, anxiety, and sleep disturbances mediate the effect of pain impact on depression. Methods: 1245 members of the National Multiple Sclerosis Society completed two scales assessing pain interference: Brief Pain Inventory (BPI) and Pain Impact Questionnaire (PIQ); 3 scales assessing fatigue: Modified Fatigue Impact Scale (MFIS), Fatigue Severity Scale (FSS), and Multidimensional Assessment of Fatigue (MAF); 2 scales assessing depression: Center for Epidemiologic Studies Depression Scale (CES-D) and Patient Health Questionnaire (PHQ-9); 2 scales assessing sleep: Medical Outcomes Survey (MOS-SAD) and Women's Health Initiative Insomnia Rating Scale (WHIIRS); and one scale for anxiety: Hospital Anxiety and Depression Scale (HADS). The model was controlled for age, gender, disability status, and social support. Results: Standardized factor loadings were moderate to high and statistically significant for Fatigue (FSS=0.83, MFIS=0.90, MAF=0.86), Sleep Disturbance (WHIIRS=0.66, MOS-SAD=-0.73), Pain Impact (PIQ=0.88, BPI=0.92), and Depression (CES-D=0.94, PHQ-9=0.91). All standardized direct effects were significant, including Pain Interference on Anxiety (0.51), Fatigue (0.56), and Sleep Disturbance (0.63); Anxiety on Depression (0.39); Sleep Disturbance on Fatigue (0.21) and Depression (0.22); and Fatigue on Depression (0.45). Standardized indirect effects of Pain Interference on Depression totaled 0.65. R2 for Pain Interference=0.21, Anxiety=0.33, Fatigue=0.57, Sleep Disturbance=0.40, and Depression=0.79. Model fit was adequate [X2=343.3(df=49), p<0.05, RMSEA=0.069, CFI=0.965, TLI=0.939, SRMR=0.033]. Discussion: The majority of the effects of pain interference on depression were mediated by anxiety, fatigue, and sleep disturbance suggesting a transdiagnostic approach to treatment.