Primary Sjogren's syndrome (SS) is an autoimmune disease characterized by fatigue. Little is known about the genesis of fatigue. Fatigue is thought to represent a multidimensional concept and it is important to be able to measure it confidently. The aims were to evaluate the reliability and validity of the 20-item Multidimensional Fatigue Inventory (MFI-20) in SS and to search for factors associated with this disabling symptom.
Forty-eight women with primary SS completed the MFI-20 questionnaire. The results were compared with age-matched women with fibromyalgia (FM) and healthy controls. Convergent construct validity was assessed by correlations to a Visual Analogue Scale (VAS) for global fatigue by Spearman's correlation (r(s)). Test-retest reliability was analysed by the intraclass correlation coefficient (ICC) in 28 women. Associations between clinical variables and subscales of the MFI-20 were analysed.
The SS women scored significantly higher in all subscales of the MFI-20 compared to controls but similar to FM. The ICCs were satisfactory, ranging from 0.66 for general fatigue to 0.85 for the total score of MFI-20. All subscales correlated significantly to VAS for global fatigue, general fatigue showing the highest correlation (r(s) = 0.70). The estimated number of hours of sleep/day was significantly associated with many of the fatigue dimensions. All five subscales of the MFI-20 were inversely associated with diastolic blood pressure (BP) and two with systolic BP.
The MFI-20 was found to be a reliable and valid tool for the measurement of fatigue in primary SS. High levels of fatigue were correlated with low BP, suggesting an associated involvement of the autonomic nervous system.