Functional cognitive disorder: dementia’s blind spot

Abstract

An increasing proportion of cognitive difficulties are recognized to have a functional cause, the chief clinical indicator of which is internal inconsistency. When these symptoms are impairing or distressing, and not better explained by other disorders, this can be conceptualized as a cognitive variant of functional neurological disorder, termed functional cognitive disorder (FCD). FCD is likely very common in clinical practice but may be under-diagnosed. Clinicians in many settings make liberal use of the descriptive term mild cognitive impairment (MCI) for those with cognitive difficulties not impairing enough to qualify as dementia. However, MCI is an aetiology-neutral description, which therefore includes patients with a wide range of underlying causes. Consequently, a proportion of MCI cases are due to non-neurodegenerative processes, including FCD. Indeed, significant numbers of patients diagnosed with MCI do not ‘convert’ to dementia. The lack of diagnostic specificity for MCI ‘non-progressors’ is a weakness inherent in framing MCI primarily within a deterministic neurodegenerative pathway. It is recognized that depression, anxiety and behavioural changes can represent a prodrome to neurodegeneration; empirical data are required to explore whether the same might hold for subsets of individuals with FCD. Clinicians and researchers can improve study efficacy and patient outcomes by viewing MCI as a descriptive term with a wide differential diagnosis, including potentially reversible components such as FCD. We present a preliminary definition of functional neurological disorder–cognitive subtype, explain its position in relation to other cognitive diagnoses and emerging biomarkers, highlight clinical features that can lead to positive diagnosis (as opposed to a diagnosis of exclusion), and red flags that should prompt consideration of alternative diagnoses. In the research setting, positive identifiers of FCD will enhance our recognition of individuals who are not in a neurodegenerative prodrome, while greater use of this diagnosis in clinical practice will facilitate personalised interventions.

A practical review of functional neurological disorder (FND) for the general physician

“…22 Recently proposed diagnostic criteria define functional cognitive disorder on the basis of positive features of internal inconsistency. 25 Cognitive testing has poor specificity in this group of patients who may excel in tests despite disabling symptoms, or who may perform in mild or even severe impairment ranges despite good occupational function. In contrast, examination of behaviour and language during the consultation seems effective in discriminating functional from neurodegenerative cognitive symptoms: those with functional symptoms are more likely to attend alone, to be distressed about their symptoms and to give richer and more specific accounts of memory failures than those with neurodegenerative disease.…”

Differentiating Functional Cognitive Disorder from Early Neurodegeneration: A Clinic-Based Study

“…However, a tertiary memory clinic study found FCD symptoms generally persisted over 20 months’ follow up [ 6 ]. A positive diagnosis of FCD is important to facilitate development of evidence based treatments (currently none exist), and also to avoid inappropriate inclusion of people with FCD in studies of neurodegenerative disease [ 7 ].…”

When dementia is misdiagnosed

“…An increasingly recognised group of people who have been diagnosed with mild cognitive impairment or early dementia have functional cognitive disorder. This is characterised by complaints of cognitive impairment symptoms that are internally inconsistent, show stability over prolonged periods of time and fail to respond to reassurance of evidence for lack of objective cognitive deficit 11 . This diagnosis represents the most likely explanation for many individuals who have received a dementia diagnosis but show no discernible deterioration in cognitive functioning or disability over several years.…”