Functional cognitive disorder is diagnosed positively on internal inconsistency. A patient who attends alone, gives a highly detailed and well organized account of memory failures, often with notes or a diary, and who continues to work and drive at a high level, is demonstrating within the consultation the very memory and executive capacities he reports losing. Answering "I do not know" and then producing the correct answer after a pause is a further inconsistency, reflecting reduced confidence and excessive self-monitoring rather than a storage deficit.
The contrast with degenerative disease is instructive. In Alzheimer disease the patient typically underestimates the problem, is brought by a relative who supplies the history, and shows failures of recall that are consistent across the interview and testing. In functional cognitive disorder attention is diverted from automatic processes to conscious monitoring, so overlearned tasks become effortful and error-prone precisely when they are attended to. Contributing factors such as poor sleep, pain, anticholinergic and sedating medication, anxiety and depression are common and should be addressed, but they are aggravators rather than the diagnostic basis.
Distinguishing functional cognitive disorder from early neurodegeneration is expected of a PGY-3 or PGY-4, so this item sits at the Intermediate level of RITE content. Giving a positive diagnosis matters because these patients otherwise accumulate repeated investigation and may be wrongly labelled with prodromal dementia.
Incorrect Answers
- A. Subjective word-finding and name retrieval difficulty is extremely common in the general population and occurs in normal ageing, anxiety and early degenerative disease.
- B. Poor sleep and amitriptyline are relevant aggravating factors that should be modified, but they do not themselves establish the diagnosis.
- C. Absence of an informant history is supportive context but is a negative feature; the diagnosis rests on demonstrable inconsistency.
- D. Young-onset Alzheimer disease and frontotemporal dementia both present in the sixth decade, so age alone does not exclude neurodegeneration.
Testing Pearls
- Functional cognitive disorder is diagnosed by internal inconsistency, not by exclusion.
- Attending alone with a detailed written list of symptoms is characteristic.
- Patients with degenerative dementia typically underestimate deficits and are brought by an informant.
- Answering "I do not know" then giving the correct answer suggests impaired confidence, not storage.
- Sleep disturbance, pain, sedating drugs and mood disorder are common aggravating factors.
References
- Jankovic J, Mazziotta JC, Newman NJ, Pomeroy SL, editors. Bradley and Daroff's Neurology in Clinical Practice. 8th ed. Philadelphia, PA: Elsevier; 2022. p. 2085-2086.
- Ball HA, McWhirter L, Ballard C, Bhome R, Blackburn DJ, Edwards MJ, et al. Functional cognitive disorder: dementia's blind spot. Brain. 2020;143(10):2895-2903.
- Stone J. Functional neurological disorders: the neurological assessment as treatment. Pract Neurol. 2016;16(1):7-17.
