Neurocognitive problems are one of the most frequent and disabling symptoms associated with ME/CFS. In one investigation, 89% of patients reported memory/concentration problems, while in another large study memory/attention deficit problems were reported by approximately 90% of 2,073 consecutive patients. Crucially, patients often report that their cognitive problems can be made worse by physical or mental exertion. But do such self-reported anecdotes about cognitive symptoms also show up as measurable deficits on objective cognitive testing in a clinical setting?
Meta-analysis is a method of combining results from a range of studies to obtain an overall estimate of the “true” effect of a treatment. Researchers at the University of Adelaide, South Australia have now published (in Psychological Medicine) a meta-analysis of all relevant clinical trials examining cognitive functioning in people with ME/CFS, with the aim of identifying the pattern and magnitude of these deficits. Overall, they found a very mixed bag of 50 studies (made up of 1,577 patients and 1,487 controls) published between 1988 and 2008 from which, nevertheless, a clear and very revealing pattern emerged on detailed examination.
The most significant cognitive deficits (see Graph above) were found in “attention” (encompassing attention span and working memory), “memory” (examined from verbal and visual memory tests, mostly memory for word lists) and reaction time (assessed as responses to both simple and complex choice stimuli). These results were consistent with the memory and concentration problems that patients themselves complain about. In contrast, there were no apparent deficits on tests of “fine motor speed”, “vocabulary”, “reasoning” or “global functioning”, suggesting that the “higher order” cognitive abilities such as language, reasoning and intelligence remain unimpaired. Importantly, most studies that examined the impact of self-reported depression on cognitive functioning failed to find a relationship, indicating that depression was not responsible for most cognitive impairments.
The range of these studies and the clarity of the findings leave no doubt that people with ME/CFS have moderate to large impairments in simple and complex information processing speed, and in tasks requiring working memory over a sustained period of time. As the authors point out, the deficits in performance are around 0.5 to 1.0 standard deviations below that of healthy people, a fact which explains the significant impact cognitive problems have on patients’ day-to-day activities and quality of life.
Reference: Cognitive functioning in chronic fatigue syndrome: a meta-analysis. Cockshell SJ, et al. Psychol Med 2010 Aug; 40(8): 1253-67.