Introduction: Appropriate management of fatigue relies upon comprehensive assessment instruments and timely delivery of targeted interventions. The aims of this study were to translate a commonly used English-language measure of fatigue in cancer patients (the Multidimensional Fatigue Symptom Inventory–Short-Form, or MFSI-SF) into European Portuguese and to evaluate the psychometric properties (internal consistency reliability, factorial structure, and discriminant, convergent and criterion concurrent validity) of the translated measure for use with Portuguese patients.
Material and Methods: After translation and adaptation of the MFSI-SF to European Portuguese, 389 participants (68.38% women), with a mean age of 59.14 years, completed the study protocol. This sample included 148 patients in active cancer treatment from a cancer center and a community sample composed of 55 cancer survivors, 75 patients with other chronic diseases, and 111 healthy controls.
Results: The European Portuguese version of the Multidimensional Fatigue Symptom Inventory-Short Form (IMSF-FR) showed strong internal consistency (Cronbach’s alpha = 0.97, McDonald’s omega = 0.95). An exploratory factor analysis indicated that the items loaded in a 5-factor model in subscales were similar to the original version. Strong correlations between the IMSF-FR and other measures of fatigue and vitality confirmed convergent validity. Discriminant validity was supported by weak-to-moderate correlations between the IMSF-FR and measures of sleepiness, propensity to sleep, and lapses of attention and memory. The IMSF-FR accurately distinguished cancer patients from healthy controls and was able to differentiate clinician rated levels of performance among cancer patients.
Conclusion: The IMFS-FR is a reliable and valid tool to assess cancer-related fatigue. By providing integrated comprehensive characterization of fatigue, this instrument may assist clinicians implementing targeted interventions.

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