Background Fibromyalgia (FM) is a disorder characterized by chronic widespread pain and tenderness and has been estimated to affect approximately 5.0 million individuals in the general United States population. Patients with FM often experience other symptoms, such as fatigue, impaired sleep and mood, cognitive dysfunction, physical functioning limitations, and reduced quality of life. Beyond pain, fatigue is commonly identified as one of the most bothersome and disabling symptoms. Currently, there is no measure of FM-related fatigue that meets FDA requirements for Patient Reported Outcome (PRO) development. Despite the lack of a standard definition of fatigue, there is a growing body of literature suggesting that fatigue is a multi-dimensional concept recognized by both the clinical and regulatory community. There is therefore a need for a well-developed PRO instrument that captures the multiple facets of FM-related fatigue for use in clinical trials.
Objectives To evaluate in-depth qualitative research to gain a full understanding of the patient experience of FM-related fatigue, and to use this to inform the development of a multi-dimensional measure of fatigue in FM.
Methods Previous research that had been conducted as part of the development of a 5-item measure of the core symptom of fatigue – the Daily Diary of Fatigue Symptoms – Fibromyalgia (DFS-Fibro) was reviewed to inform the development and expansion of this measure in order to incorporate multiple aspects of fatigue. This involved a comprehensive literature search, clinical expert input, and patient-input through open-ended, exploratory, concept elicitation interviews conducted with 40 FM patients in the US (N=20), France (N=10), and Germany (N=10); and a further 20 cognitive debriefing interviews conducted in 20 FM patients in the US. Participants in both groups of interviews were mostly female (70% and 85%, respectively) with a mean age of 48.7 years and 58 years respectively.
Results The conceptual model of the patient experience of FM-related fatigue developed from the in-depth concept elicitation interviews demonstrated that fatigue is a multi-faceted experience. A multi-dimensional framework was developed to represent the five domains of FM-related fatigue that emerged from the qualitative research: the global experience of fatigue, cognitive fatigue, physical fatigue, motivation, and impact on function. The original pool of items, capturing all elements of fatigue that emerged from the qualitative work, was then evaluated in light of the multi-dimensional framework. The findings supported the need for a comprehensive measure of FM-related fatigue; items representing these additional concepts were then generated to form a 17-item measure of FM-Fatigue.
Conclusions A 17-item multidimensional measure (Daily Diary of Fatigue Symptoms-Fibromyalgia-17 item; DFS-Fibro-17]), made up of 5 domains (Global Fatigue Experience, Cognitive Fatigue, Physical Fatigue, Motivation, and Impact on Function), is being developed. The next stage is to evaluate this longer version of the measure to confirm sound psychometric properties and best fit with the data in FM patients.
Acknowledgements CB and TS were formerly employees of Pfizer Ltd, copyright owners of the DFS-Fibro.
Disclosure of Interest None declared