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A unifying theory for cognitive abnormalities in functional neurological disorders, fibromyalgia and chronic fatigue syndrome: systematic review
  1. Tiago Teodoro1,2,3,
  2. Mark J Edwards1,2,
  3. Jeremy D Isaacs1,2
  1. 1 Neurosciences Research Centre, Molecular and Clinical Sciences Research Institute, St George’s, University of London, London, UK
  2. 2 Department of Neurology, St George’s University Hospitals NHS Foundation Trust, London, UK
  3. 3 Instituto de Medicina Molecular Faculdade de Medicina, Universidade de Lisboa & Serviço de Neurologia Hospital de Santa Maria, Lisboa, Portugal
  1. Correspondence to Dr Jeremy D Isaacs, Department of Neurology, St George’s Hospital, London SW17 0QT, UK; jeremy.isaacs{at}


Background Functional cognitive disorder (FCD) describes cognitive dysfunction in the absence of an organic cause. It is increasingly prevalent in healthcare settings yet its key neuropsychological features have not been reported in large patient cohorts. We hypothesised that cognitive profiles in fibromyalgia (FM), chronic fatigue syndrome (CFS) and functional neurological disorders (FNDs) would provide a template for characterising FCD.

Methods We conducted a systematic review of studies with cognition-related outcomes in FM, CFS and FND.

Results We selected 52 studies on FM, 95 on CFS and 39 on FND. We found a general discordance between high rates of subjective cognitive symptoms, including forgetfulness, distractibility and word-finding difficulties, and inconsistent objective neuropsychological deficits. Objective deficits were reported, including poor selective and divided attention, slow information processing and vulnerability to distraction. In some studies, cognitive performance was inversely correlated with pain, exertion and fatigue. Performance validity testing demonstrated poor effort in only a minority of subjects, and patients with CFS showed a heightened perception of effort.

Discussion The cognitive profiles of FM, CFS and non-cognitive FND are similar to the proposed features of FCD, suggesting common mechanistic underpinnings. Similar findings have been reported in patients with mild traumatic brain injury and whiplash. We hypothesise that pain, fatigue and excessive interoceptive monitoring produce a decrease in externally directed attention. This increases susceptibility to distraction and slows information processing, interfering with cognitive function, in particular multitasking. Routine cognitive processes are experienced as unduly effortful. This may reflect a switch from an automatic to a less efficient controlled or explicit cognitive mode, a mechanism that has also been proposed for impaired motor control in FND. These experiences might then be overinterpreted due to memory perfectionism and heightened self-monitoring of cognitive performance.

  • functional neurological disorder
  • memory
  • cognition
  • chronic fatigue syndrome
  • pain

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  • Contributors The study was conceived by JDI and MJE; TT performed data acquisition and wrote the first draft, which was revised by JDI and MJE; all authors contributed to study design, data interpretation and approving the final version of the manuscript.

  • Funding This work was supported by the Wellcome Trust (204809/Z/16/Z), Medical Research Council and Fundação para a Ciência e Tecnologia (SFRH/SINTD/95267/2013).

  • Competing interests None declared.

  • Patient consent Not required.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement There is no additional unpublished data from this study.

  • Correction notice Since this paper was first published online the third affiliation has been updated.