Validity and reliability of the German multidimensional fatigue inventory in spinal muscular atrophy

Abstract

Objective Fatigue is a common and burdensome symptom of spinal muscular atrophy. Given its complex interactions, different dimensions of fatigue need to be investigated. The Multidimensional Fatigue Inventory is a widely used instrument that captures five distinct dimensions. The aim of this study was to investigate the validity and reliability of the German Multidimensional Fatigue Inventory in spinal muscular atrophy and to evaluate the presence of clinically relevant fatigue. Methods One hundred and forty adult spinal muscular atrophy patients completed the Multidimensional Fatigue Inventory in a nationwide, multicenter, cross‐sectional study. Structural validity was explored using principal component analysis. Cronbach’s α was calculated to evaluate internal consistency. Convergent validity was assessed by correlation with a Visual Analog Scale for fatigue and the EuroQol‐Five Dimension‐Five Level Scale as a measure of quality of life. Results The original five‐component model of the questionnaire constituted an acceptable fit. Internal consistency and convergent validity of general, physical, mental fatigue, and reduced activity were good. We observed a floor effect for mental fatigue. While physical fatigue exceeded the cutoff for clinically relevant fatigue, all dimensions but reduced motivation correlated negatively with quality of life. Age, depression, and ≥4 copies of the survival motor neuron 2 gene were associated with higher general/physical fatigue; unemployed participants reported higher scores for reduced activity/motivation. Interpretation The Multidimensional Fatigue Inventory is a valid and reliable instrument to assess different dimensions of fatigue in spinal muscular atrophy. Fatigue is a relevant problem in spinal muscular atrophy and its assessment should be incorporated into standard care.

Psychometric properties, factor structure, and German population norms of the multidimensional fatigue inventory (MFI-20)

“…Reduced motivation showed the lowest internal consistency, which is in line with many studies ( 16 ). Mental fatigue showed the lowest interscale correlations with the other subscales.…”

“…The highest interscale correlations were found between physical fatigue and general fatigue, and physical fatigue and reduced activity, exactly as in other studies (1,31). This is in line with reported difficulties to distinguish between general and physical fatigue (16) and argues for combining these two subscales or even for using the entire unidimensional structure of the MFI-20. Since even the lowest subscale × total score correlation is higher than any inter-subscale correlation in our data, it could be that "the MFI-total is a more valid score for fatigue than the single MFI-subscale scores" (31).…”

“…In a sample of cancer patients receiving radiotherapy, 28.6% showed a ceiling effect in general fatigue and 17.3% showed a floor effect in mental fatigue ( 33 ). In a sample of patients with spinal muscular atrophy, 19.3% exhibited a floor effect in mental fatigue ( 16 ). These strong differences in percentages of floor and ceiling effects between the subscales, even within samples, question the homogeneity of the latent construct underlying the MFI-20 .…”

“…This structure is strongly questioned by many studies, finding a three-, four- or five-factor structure with varying item loadings [refer to ( 11 ) for an overview]. A recent German study of patients ( n = 140) with spinal muscular atrophy, however, confirmed the five-factor structure using principal component analysis ( 16 ). They explained 62.2% of the variance, and only five of the 20 items did not load on the components that otherwise matched the original MFI-20 subscales.…”

Assessing the Assisted Six-Minute Cycling Test as a Measure of Endurance in Non-Ambulatory Patients with Spinal Muscular Atrophy (SMA)

“…Perceived fatigue was assessed with the Fatigue Severity Scale (FSS), a validated PRO in SMA for determining the impact of an individual's recalled fatigue experience in the past week [38,39]. FSS assesses an overall exhaustion levels in conjunction with The primary variable evaluated in the A6MCT was distance, which is represented by the cumulative revolutions an individual completed at the end of 6 min, providing insight into patient endurance.…”