Cognitive FND
Functional cognitive impairment refers to persistent and internally inconsistent cognitive symptoms that cannot be explained by any other neurodegenerative condition (Ball et al., 2020). Functional cognitive impairment is likely to be very common, but is rarely diagnosed because such patients also meet the criteria for either mild cognitive impairment or subjective cognitive decline.
Positive evidence of cognitive internal inconsistency is shown when reported subjective cognitive difficulties and/or low scores on standardised tests are in direct conflict:
observations during a clinical psychology interview or reported activities, such as working in a cognitively demanding occupation,
with specific patterns in neuropsychological test results showing that cognitive processes work much better when accessed in a less explicit way; e.g. patients have a better ability to delayed recall of information than their initial registration.
Diagnostic criteria according to Ball et al., (2020)
At least one or more simptomov of impaired cognitive functioning
Any cognitive functioning problem that can also be seen in "organic" cognitive disorders such as dementia and stroke. All cognitive domains may be involved, from memory, concentration (sustained attention, processing speed), executive functions (planning, organising, processing speed), language difficulties (e.g. functional aphasia), orientation, visual and spatial processing difficulties, reading and word finding.
Ideally, cognitive functioning is assessed by standardised neuropsychological testing by an experienced and appropriately qualified neuropsychologist. In doing so, it is important that the neuropsychologist considers the bigger picture, which includes:
history of cognitive symptoms (fluctuation; are symptoms static or have they worsened over time?).
nature of cognitive symptoms and type of symptoms (ask the patient about real-life examples; the impact of symptoms on their functioning in everyday life - impact on work, relationships, hobbies, driving),
ruling out organic causes, that could explain the symptoms (e.g. fatigue, sleep disturbances, previous stroke, illness, medication).
assessment of psychological conditions that may affect cognition (e.g. depression, anxiety, beliefs about self-reported symptoms - memory perfectionism),
comparison of self-reported symptoms and relatives' reports of symptoms,
development history (e.g. traumatic experiences, psychosocial functioning, defence mechanisms, etc.).
Evidence of cognitive internal inconsistency
Cognitive internal inconsistency is diagnosed when a patient reports significant cognitive difficulties or has extremely low scores on standardised tests, but e.g. simultaneously performs cognitively demanding work that requires optimal cognitive functioning and/or reports that cognitive difficulties have no impact on his/her daily functioning.
Cognitive symptoms cannot be explained by another psychiatric or neurological disorder
The criterion assumes that the patient's symptoms cannot be explained by another (neuro)psychiatric disorder such as Alzheimer's dementia or stroke.
However, this does not mean that a patient cannot have an associated disorder to meet this criterion. In this case the associated disorder does not explain, or at least does not fully explain, the observed symptoms.
However, it is important to note that in clinical practice, functional cognitive symptoms are often associated with psychological conditions such as depression and anxiety (social anxiety, generalised anxiety and panic attacks), and these disorders explain such symptoms.
Patients often do not perceive psychological distress, due to their tendency to dissociate and/or their inability to express emotions verbally. It is important to realise that patients do not do this on purpose, but that it is a protective mechanism of the brain against psychological vulnerability.
It is also crucial to note that functional cognitive symptoms can be explained by other and often overlooked factors, such as: a) sleep deprivation; b) dehydration; c) vitamin and mineral deficiencies; d) polypharmacy; e) side-effects of medicines.
Cognitive symptoms are a major distress for the patient and affect their daily functioning in important areas of life (social, work, emotional, etc.).
Cognitive symptoms can cause severe distress for some patients (e.g. making it impossible for them to take care of themselves, be independent, drive, do their job, take prescribed medication, etc.), while there is also a subgroup of people who do not experience cognitive symptoms as distressing.
Some concerns about the diagnostic criteria
The criterion of "internal cognitive inconsistency" can make patients feel that they are simulating their symptoms and that no one believes them. Beliefs that no one believes them may even perpetuate functional symptoms, which makes it reasonable to ask to what extent such a criterion is clinically useful or even harmful for symptom management. It is important to explain the disorder to the patient in an appropriate and sympathetic way and to tell him that there is a temporary blockage of memories and not a permanent memory impairment.
A diagnosis of functional cognitive impairment tells us nothing about the link between the patient's emotional and cognitive functioning and does not explain the factors that perpetuate symptoms (e.g. certain beliefs, memory perfectionism, etc.) or coping strategies (e.g. protective factors and dissociation mechanisms).
There is also a clear inconsistency between the criteria themselves, and it is possible that patients may not meet all the criteria but still experience symptoms of functional cognitive impairment (van Der Hulst, 2023).
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Ball, H. A., McWhirter, L., Ballard, C., Bhome, R., Blackburn, D. J., Edwards, M. J., ... and Carson, A. J. (2020). Functional cognitive disorder: dementia's blind spot. Brain, 143(10), 2895-2903.
van der Hulst, E. J. (2023). A Clinician's Guide to Functional Neurological Disorder: A Practical Neuropsychological Approach. Routledge.