The investigators evaluated a range of neuropsychological tasks that covered the main attentional and executive areas. Subjects (n=110 with fibromyalgia, n=33 with depression and n=50 healthy controls) enrolled themselves in the study, and investigators acknowledge that their results may reflect some selection bias.
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“In this study, we provide new evidence to further our understanding of the effects of fibromyalgia on cognitive performance,” write the authors in their discussion. “We have done this [by] separating the attributable effects of potential confounding variables and, in particular, the effects explained by depressive symptoms, and by also taking into account the influence of anxiety and sleep dysfunction.” They began their research by noting that a large difference existed between patients with fibromyalgia and healthy controls in measurements related to depression, anxiety and sleep quality. Moreover, fibromyalgia was associated with a worse quality of sleep than depressive disorder.
“With regard to the specific objectives of the study in terms of cognitive performance, the first finding was that the differences initially found between the fibromyalgia and the healthy groups in the majority of the cognitive measurements subsequently disappeared when we adjusted for depression, anxiety and sleep quality, leaving only differences in the Stroop Interference task,” the authors explain.
The Stroop test uses cards to measure automatic processing speed, controlled processing speed and cognitive flexibility. The interference index is calculated from this test and used as a measure of inhibition ability. “This lack of difference in most of the cognitive tests supports our main hypothesis that the differences in cognitive performance between groups could mainly be explained by depression for most cognitive domains,” continue the authors.
Although patients with fibromyalgia and those with depression showed similar levels of performance in most of the cognitive tests, notable differences were demonstrated. Short-term and working memory and inattention measures were associated with only symptoms of depression. Selective attention was associated with both depression and fibromyalgia. In contrast, cognitive flexibility and inhibition abilities were specifically associated with fibromyalgia.