Validation of the Modified Fatigue Impact Scale in Parkinson's disease
Introduction
Fatigue is a common symptom in Parkinson's disease (PD) with prevalence rates of 33–70% [1]. While there is no universally accepted definition of fatigue, it has been defined as a “feeling of abnormal and overwhelming tiredness and lack of energy, distinct both qualitatively and quantitatively from normal tiredness” [2]. It is generally accepted that fatigue is multidimensional and may be comprised of distinct constructs including physical and cognitive fatigue.
The most prevalent method of assessing fatigue is by self-report rating instruments. Recently, the International Movement Disorders Society (IMDS) task force on fatigue rating scales reviewed all nine fatigue-specific rating instruments that had been used in previous PD studies [3]. Only two scales, the Fatigue Severity Scale (FSS) [4] and the Multidimensional Fatigue Inventory (MFI) [5] were “recommended” for rating fatigue severity in PD. The FSS is a brief, nine-item unidimensional scale that does not specifically measure cognitive fatigue. While the MFI addresses a larger array of items, including cognitive (mental) fatigue, it does not evaluate the impact of fatigue on functioning. Rather, the MFI measures fatigue by sampling items that could be caused by alternative etiologies, rather than fatigue. For example, the MFI requires individuals to rate whether they can concentrate well or if their thoughts wander, difficulties that may be due to cognitive dysfunction, rather than fatigue per se. The IMDS acknowledged that their recommendations were limited by the lack of published studies on certain scales [3], suggesting that research on alternative measures of fatigue in PD may be warranted.
One scale that has not been used or evaluated in PD is the Modified Fatigue Impact Scale (MFIS), a 21-item self-report measure of fatigue derived from the 40-item Fatigue Impact Scale [6]. The Multiple Sclerosis Council for Clinical Practice Guidelines recommends the MFIS for use in clinical practice and research [7] and empirical studies have supported the utility of the MFIS in multiple sclerosis patients [8]. In contrast to the FSS and MFI, the MFIS is a multidimensional measure that assesses the impact of fatigue on physical, cognitive, and psychosocial function. In addition, the MFIS contains six additional items on each of the cognitive (mental) and physical subscales compared to the MFI, suggesting the possibility of a stronger and more thorough assessment of these factors.
The aim of this study was to evaluate the utility of the MFIS in PD by examining the factor structure of the scale, internal consistency of the scale items, as well as convergent and divergent validity of the MFIS in a nondemented PD sample.
Section snippets
Participants
Participants were one hundred individuals diagnosed with PD by a board-certified neurologist specializing in Movement Disorders based on the UK Brain Bank criteria [9]. PD patients were recruited from the Movement Disorders Clinics at the University of California, San Diego (UCSD) and the VA San Diego. Each patient was determined to be nondemented based on a clinical assessment using the Diagnostic and Statistical Manual of Mental Disorders-IV criteria [10] and the criteria set forth by Emre
Results
There were no significant correlations between the MFIS total score and age (rs = −0.153, p = 0.13), education (rs = −126, p = .21), or disease duration (rs = 0.040, p = .69). Males and females did not significantly differ on their total MFIS scores (t (98) = −0.585, p = .56).
The PCA revealed two factors that had eigenvalues > 1.0. These factors were rotated using the varimax rotation procedure that yielded two interpretable factors, which we term “cognitive” and “physical/social” based on the
Discussion
The MFIS appears to be a promising measure for evaluating multidimensional fatigue in nondemented individuals with Parkinson's disease. Our results confirmed that all 21 items that comprise the MFIS were homogenous. Our findings also revealed that the 9 items that comprised the original physical subscale loaded onto one factor and the items that comprised the original cognitive subscale loaded onto another factor, with the exception of “alertness”, in which the difference was too small to
Acknowledgments
This study was supported by a VA Merit Award (J.V.F.) and VA Career Development Awards (D.M.S. and C.R.A.). We would like to acknowledge Kristalyn M. Obtera, Mathes M. Burke III, and Shannon Earl for their help with data collection and compilation. We would also like to thank the patients, staff, and volunteers associated with the VASDHS and UCSD for their involvement in this study.
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