Fibromyalgia (FM) is characterized by myriad symptoms and problems. Fatigue is one of the most common, distressing, and disabling symptoms in FM. The purpose of this study was to use fatigue item banks that were developed as part of the Patient-Reported Outcomes Measurement Information System (PROMIS) to devise a self-report measure of fatigue for use in individuals with FM.
A sample of 532 adults with FM (age range = 18-77, 96.1 % female) completed the PROMIS fatigue item bank. Factor analyses and item response theory analyses were used to identify dimensionality and optimally performing items. These data were used in combination with clinical input to select items for a fatigue self-report measure for use in FM.
Factor analyses revealed four distinct factors in the PROMIS fatigue item bank; items for each univariate subscale were identified by selecting four items with high item information values. A 16-item measure, the PROMIS FatigueFM Profile, consisting of four 4-item short forms reflecting fatigue experience ("intensity") and fatigue impact in three subdomains-social, cognitive, and motivation-was created. The new PROMIS FatigueFM Profile short forms showed excellent internal reliability, low ceiling and floor effects, and equivalent or higher test information compared to the standard 4- and 7-item PROMIS fatigue short forms.
The newly developed PROMIS FatigueFM Profile, a 16-item measure consisting of four 4-item short forms of self-reported fatigue severity, shows early evidence of good psychometric characteristics, provides the ability to use short forms that assess distinct aspects of fatigue experience and fatigue impact, and demonstrates equivalent or higher levels of test information compared to standard PROMIS fatigue short forms with similar number of items. The PROMIS FatigueFM Profile indicated fatigue experience and impact levels approximately 1.5 standard deviations above the normative sample mean across all short forms. Future work to evaluate the validity and reliability of this new measure in individuals with FM is needed.