Role of frailty in the assessment of cognitive functioning
Introduction
The neuropsychological assessment constitutes a cornerstone of the clinical approach to cognitive disturbances (Lezak et al., 2004). It allows the objective and standardized measurement of the individual’s cognitive abilities and deficits, thus indirectly yielding information about the structural and functional integrity of the brain regions and networks. In other words, it plays a major role in the diagnostic definition of dementia and other cognitive disorders (e.g., mild cognitive impairment), also supporting the discrimination of the different etiologies, the longitudinal tracking of the condition, as well as orienting clinical and therapeutic choices (Sorbi et al., 2012).
Tests included in the traditional neuropsychological assessment are usually aimed at examining (alone or in combination) independent cognitive domains that are thought to be sub-served by distinct neuroanatomical structures (Rascovsky, 2016). Nevertheless, the relationship between neuropsychological test and the pertaining cognitive tasks (and, consequently, the underlying neural substrates) may not be as “pure” as theoretically described. For instance, numerous sociodemographic determinants (i.e., age, education, or -to a lower extent- ethnicity and gender) are important predictors of the individual’s performance for most neuropsychological tests (Ganguli et al., 2010). Therefore, in order to properly interpret the findings of the neuropsychological examination, raw scores are frequently converted into standardized scores by correcting for these potential confounders. Along the same lines, it can be hypothesized that biological factors may similarly and independently affect the relationship between neuropsychological tests and the examined cognitive functions. In fact, the performance at a given test may not unequivocally reflect the cognitive reserves and deficits of the individual, but also include (at least part of) his/her biological asset.
In this context, the construct of frailty (i.e., the age-related exhaustion of homeostatic reserves, determining a state of increased vulnerability to stressors) may offer an opportunity for better weighting the results of traditional tests. In fact, by measuring a surrogate of biological aging, frailty may nest a comprehensive evaluation of the organism’s status in the profiling of the individual. In particular, the frailty model proposed by Rockwood and Mitnitski based on the age-related accumulation of deficits (Mitnitski et al., 2001), seems specially suitable for this use because ad hoc designed for capturing the biological complexity of the person in a single, comprehensive variable (the so-called Frailty Index [FI]).
In the present study, it is hypothesized that neuropsychological tests are differently affected by the underlying biological status of the tested individual. As such, there might be instruments that more than others may require a careful contextualization of their results with the person’s biological status (Fig. 1, first hypothesis). In parallel, frailty could act as a moderator in the relationship between specific neuropsychological domains and the overall cognitive functioning of the individual. That is, the biological complexity of the subject could influence his/her global cognitive performance in relation to the impairment in specific neurocognitive functions and measures (Fig. 1, second hypothesis). To address these two hypotheses, the relationships between a wide set of routinely adopted neuropsychological measures and a FI are evaluated in a sample of subjects referred to a memory clinic. The influence of the FI in the relationship between neuropsychological tests and global cognition is explored.
Section snippets
Methods
All participants included in the present analyses had been referred to the Memory Clinic of the Department of Human Neuroscience, “Sapienza” University of Rome (Rome, Italy) because complaining cognitive disturbances. Data from the neurological and neuropsychological assessments conducted at their first evaluation (occurred between January 2018 and April 2018) were considered for the present analysis. Patients and caregivers (or legal guardians when necessary) provided written informed consent
Results
A total of 79 subjects (mean age 71.5, SD 6.3; women 55.7%) underwent the neurocognitive and clinical assessment. Most of them were in general good health conditions, as also suggested by the relatively low FI score (median 0.15; Annex 2 in Supplementary data). Only nine of them resulted as frail (defined as presenting a FI equal to or higher than 0.25 (Kelaiditi et al., 2016)). A statistically significant correlation was found between age and FI scores (Spearman’s rho 0.31; p < 0.01).
Discussion
In the present study, the relationships between multiple neuropsychological tests and a 35-item FI were explored. Moreover, the moderating role of the FI in the association between individual neuropsychological domains and the overall cognitive functioning was investigated.
Results show that the interpretation of the neuropsychological assessment might be biased by the frailty status of the tested individual. In fact, despite the relatively healthy condition of our sample population, a
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