A unifying theory for cognitive abnormalities in functional neurological disorders, fibromyalgia and chronic fatigue syndrome: systematic review

Abstract

BackgroundFunctional 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.MethodsWe conducted a systematic review of studies with cognition-related outcomes in FM, CFS and FND.ResultsWe 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.DiscussionThe 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.

Neuropsychological dysfunction in chronic fatigue syndrome and the relation between objective and subjective findings.

“…Thus, our results support some previous studies that show discrepancies between subjective and objective cognitive measures in CFS (Cockshell & Mathias, 2014;Cvejic, Lloyd, & Vollmer-Conna, 2016;Krupp, Sliwinski, Masur, Friedberg, & Coyle, 1994;Short et al, 2002;Teodoro et al, 2018). Several explanations for these discrepancies have been proposed by different authors.…”

“…Others have suggested that they overestimate their premorbid cognitive performance, like the "good-old-days" phenomenon (Sullivan & Edmed, 2012). The results also indicated that CFS might mimic functional cognitive disorder (FCD), i.e., a condition which has been suggested to have a subjective experience of cognitive dysfunction in the absence of underlying brain pathology Teodoro et al, 2018).…”

Speech, language and swallowing impairments in functional neurological disorder: a scoping review

“…This means that functional communication and swallowing disorders may go underdiagnosed and consequently under-reported. Currently, functional communication and swallowing disorders are a diagnosis of exclusion (De Letter et al 2012, Teodoro et al 2018, Kim et al 2018. Further research is needed to validate a set of positive diagnostic criteria for SLTs to use both within clinical and research practice.…”

Management of functional neurological disorder

“…There is a high frequency of pain, including chronic migraine, fatigue and the subjective sense of "cognitive fog" in patients with FND [45][46][47]. Although distinct entities, there appears to be significant overlap with FND, fibromyalgia (FM) and chronic fatigue syndrome (CFS), particularly in the way patients describe subjective cognitive difficulties, perhaps underpinned by excessive attention towards the body, severe pain and fatigue [48]. It is necessary to recognize and treat these symptoms as part of FND, as they may be acting as either triggering or maintaining factors in FND.…”