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Factor analysis of unexplained severe fatigue and interrelated symptoms: overlap with criteria for chronic fatigue syndrome

Nisenbaum R, Reyes, M, Mawle AC, Reeves WC.
Factor analysis of unexplained severe fatigue and interrelated symptoms: overlap with criteria for chronic fatigue syndrome.
American Journal of Epidemiology, vol. 148, pages 72-77, 1998.

Summary

Controversy exists about the duration of fatigue in CFS and exactly which symptoms should be included to make the definition more specific. The objective of this study was to determine which groups of symptoms, if any, were most strongly correlated with unexplained severe and debilitating fatigue of >6 months and >6 months. Factor analyses of self-reported data from a population-based study of fatigue and symptoms in San Francisco, California yielded three groups of symptoms (factors) that were correlated among each other. All three of these groups were correlated with fatigue >6 months. Group 1 symptoms (mood-cognitive) included difficulty thinking or concentrating, depression, general weakness, forgetfulness, unusual fatigue post-exertion and difficulty sleeping; group 2 (flu-like) included symptoms of feverishness, chills, sore throat, tender lymph nodes and night sweats; and group 3 (visual impairment) included visual disturbances, seeing spots, and light sensitivity. No group of symptoms correlated with fatigue 6 months. These results suggest that a fatigue--mood-cognitive-flu-like and visual impairment symptom construct is present in this study population. Because of the overlap between the above symptoms and CFS criteria, the results also provide empirical support for the current definition of CFS. Finally, these findings suggest that symptoms might only cluster around fatigue of duration >6 months, but not fatigue of shorter duration.

Abstract

The objective of this study was to identify factors explaining the correlations among unexplained severe fatigue of different durations (1-5 months or >6 months) and symptoms reported as significant health problems during a preceding 4-week period. Between June and December of 1994, a cross-sectional, random-digit-dialing telephone survey was conducted among residents of San Francisco, California. All subjects who reported severe fatigue lasting for >1 month and a random sample of nonfatigued subjects were asked to participate in a detailed telephone interview. Data from 1,510 individuals, aged 18-60 years, who did not have medical or psychiatric conditions that could explain their severe fatigue were analyzed. Common factor analyses identified three correlated factors (defined as "fatigue-mood-cognition" symptoms, "flu-type" symptoms, and "visual-impairment") that explained the correlations among fatigue for >6 months and 14 interrelated symptoms. No factor explained the correlations among fatigue for 1-5 months and other symptoms. The combination of fatigue for >6 months duration and selected symptoms overlaps with published criteria used to define cases of chronic fatigue syndrome (CFS). Although symptoms described in this study were reported as appearing within the preceding month, and CFS symptoms must have been present for the past 6 months, these results provide empirical support for the interrelations among unexplained fatigue of >6 months' and symptoms included in the CFS case definition.

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