Figure 1.

How FCD relates to other cognitive concepts. (A) Where FCD fits in relation to other key terminology used in the cognitive clinic. ‘Objective cognitive impairment’ denotes low scores on standardized testing. ‘Subjective cognitive concern’ denotes an individual’s perception of their cognitive difficulties (note some patients with MCI and dementia lack insight). Patients with FCD account for a proportion of those with MCI, and a proportion of those with SCD; rarely, those with FCD can meet criteria for dementia (i.e. severe enough to interfere with daily function and independence). Crosses represent biomarkers for neurodegenerative conditions. Biomarkers are clustered most densely among patients with dementia; a small number of true positive biomarkers also exist in the healthy population with neither subjective concerns nor objective impairment (indicating neurodegenerative tendency that has not yet manifested), and some will be false positives because a biomarker with 100% specificity seems unlikely (see McWhirter et al., 2020 for further discussion). (B) Trajectories in FCD (adapted from McWhirter et al., 2020). This illustrates the wide spectrum of potential trajectories within FCD, highlighting that some patients have considerable persisting symptoms and impairment even after serial testing, whereas others return to baseline functioning. The causes of these divergent trajectories may be explicable via co-morbidities or external factors, but often no such factors are identified. Disentangling this heterogeneity is an important area for future research. The x-axis represents each lifetime; those who remain above the x-axis to the end of their lifetime have died from other causes.