Study design: This is a structured, evidence-based review of all available studies on the coexistence of fatigue and pain.
Objectives: To determine what evidence, if any, exists for or against the existence of an association between fatigue and pain and a potential etiological relationship between pain and fatigue.
Summary of background data: Pain physicians have noted fatigue as a frequent complaint in chronic pain patients (CPPs), and previous studies have reported the association of fatigue and pain.
Methods: Computer and manual literature searches for studies relating to fatigue and pain produced 23 reports. These references were reviewed in detail, and information relating to the above problems was abstracted and placed into tabular form. Each report was also categorized for the type of study it represented according to the guidelines developed by the Agency for Health Care Policy and Research (AHCPR). In addition, a list of 15 quality criteria was utilized in order to measure the quality of each study. Each study was categorized for each criterion as positive, (criterion filled), negative (criterion not filled), or not applicable independently by two of the authors. A percent quality score was obtained for each study by counting the total number of positives obtained, dividing by 15 minus the total number of not applicable, and multiplying by 100. Only studies having a quality score of 75% or greater were utilized to formulate the conclusions of this review. The strength and consistency of the evidence represented by the remaining studies was then categorized according to the AHCPR guidelines. Conclusions of this review were based on those results.
Results of data synthesis: Of the 23 reports, 17 had quality scores of 75% or greater. Of these 17 reports, 94.1% indicated that there was an association between fatigue and pain. In addition, 100% of a subgroup of 13 reports (all with quality scores of 75% or greater) indicated that there may be an etiological relationship between pain and fatigue. The overall strength and consistency of this evidence according to AHCPR guidelines was therefore categorized as A (highly consistent findings from multiple studies).
Conclusions: Based on the above results, it was concluded that there is an association between fatigue and pain and that there may be an etiological relationship between pain and fatigue. Pain physicians and other pain treatment professionals should be aware of the high prevalence of fatigue in pain patients. In addition, future research might investigate possible mechanisms for the relationship between pain and fatigue.