The researchers observed internal consistence and convergent validity, leading them to suggest the tool be incorporated as a clinical standard in spinal muscular atrophy (SMA) care.
Recent findings show that a widely used tool for measuring fatigue, a common symptom of spinal muscular atrophy (SMA), is both valid and reliable in adult patients with the disease.
The findings come from nearly 150 adult patients with SMA who completed the Multidimensional Fatigue Inventory (MFI). Across the majority of the 5 dimensions—physical fatigue, mental fatigue, general fatigue, reduced activity, and reduced motivation—the researchers observed internal consistence and convergent validity, leading them to suggest the German tool be incorporated as a clinical standard in SMA care.
Their findings were published in Annals of Clinical and Translational Neurology.
“Our results indicate that the MFI is a valid and reliable instrument to assess different dimensions of fatigue in adult SMA patients. The original 5-component model showed an acceptable fit for the data and all dimensions, but reduced motivation had good internal consistency and convergent validity,” commented the researchers. “We recommend the use of the original version of the MFI, although we found evidence that the reduction of individual items may lead to slightly improved psychometric properties.”
According to the researchers, reduced motivation showed low interitem and item scale correlations in addition to unsatisfactory Cronbach’s α (0.45), consistent with previous reports of the dimension in chronic diseases like postpolio syndrome.
In certain cases of internal consistency, the researchers found that combining multiple dimensions could increase Cronbach’s α coefficients. For example, if general and physical fatigue were combined as a single score, the Cronbach’s α would have increased from 0.76 and 0.75, respectively, to 0.84.
Convergent validity, measured by Spearman rank correlation of the dimensions with a visual analog scale, was considered satisfactory. General and physical fatigue, as expected, showed the strongest correlations with quality of life.
Results from the study also showed an apparent floor effect for mental fatigue, with nearly 20% of the patients included in the study choosing the lowest score for the dimension. There were no other floor or ceiling effects observed in the other dimensions.
Notably, patients with a more mild SMA phenotype and thus a higher amount of SMN2 copies (5 or 6) tended to have worse fatigue, particularly physical fatigue.
“In a previous monocentric study, we found that SMA patients with at least 4 SMN2 copies reported higher scores for reduced activity but not physical fatigue,” wrote the researchers. “A possible explanation for this discrepancy may be that in the present study more participants with fewer than 4 SMN2 copies—and thus, a more severe phenotype—were included and median physical fatigue was lower. Component correlations between physical fatigue and reducedactivity might also contribute to this finding, although further investigation is needed.”
Although age and depression also correlated positively with worse fatigue (general and physical), there were no significant differences in the MFI dimensions based on gender, wheelchair use, scoliosis, use of noninvasive ventilation, use of percutaneous endoscopic gastrostomy, education level, or relationship status.
There were also no significant differences based on any motor function or disability measures, which the researchers recognize is well known, although the reasoning remains unclear.
Binz C, Osmanovic A, Thomas N, et al. Validity and reliability of the German multidimensional fatigue inventory in spinal muscular atrophy. Ann Clin Transl Neurol. Published online February 22, 2022. doi:10.1002/acn3.51520