\u2018Two-level\u2019 measurements of processing speed as cognitive markers in the differential diagnosis of DSM-5 mild neurocognitive disorders (NCD)

Hanna Lu,Sandra S M Chan,Linda C W Lam

doi:10.1038/s41598-017-00624-8

Abstract

Processing speed is an updated diagnostic factor for neurocognitive disorders (NCD) in DSM-5. This study investigated the characteristics of processing speed and their diagnostic values in NCD patients. A flanker test was conducted in 31 adults with NCD due to vascular disease (NCD-vascular), 36 patients with NCD due to Alzheimer’s disease (NCD-AD), and 137 healthy controls. The processing speed was evaluated using two measurements: mean reaction time (RT) and intra-individual variability of RT. Mean RT represents the global processing speed. Intra-individual variability of RT is the short-term fluctuation of RT and consists of two indices, which are intra-individual coefficient of variation of reaction time (ICV-RT) and intra-individual standard deviations (iSD). We observed elevated ICV-RT and iSD in NCD-AD and NCD-vascular patients. Additionally, there was a slowed RT in NCD-AD patients. The intra-individual variability of RT had a moderate power to differentiate NCD subgroups. The mean RT was able to discriminate the NCD-AD from NCD-vascular patients. Our findings highlight the clinical utility of the combined ‘two-level’ measurements of processing speed to distinguish between individuals with different cognitive status. Furthermore, the ‘two-level’ features of processing speed embedded in the psychometric property may also reflect the diverse aetiology underlying certain ‘disease-specific’ neurocognitive disorders.

Highlights

In the current conceptual framework of dementia disease trajectory, the neurocognitive disorders (NCD) are a new term that replaces ‘mild cognitive impairment’ (MCI) and represents an intermediate state prior to clinical dementia[1]
We explored the correlations between mean reaction time (RT), intra-individual variability of RT, and scores on neurocognitive tests
The NCD due to Alzheimer’s disease (NCD-AD) group had the worst performance in the domain of shortterm memory

Summary

Introduction

In the current conceptual framework of dementia disease trajectory, the neurocognitive disorders (NCD) are a new term that replaces ‘mild cognitive impairment’ (MCI) and represents an intermediate state prior to clinical dementia[1]. There is intra-individual variability due to advancing age, and this variability reflects the short-term fluctuations on cognitive tests. The mean RT and intra-individual variability of RT represent the ‘two-level’ measurements of processing speed. It is currently unclear whether the two measurements of processing speed can be used to differentiate senior adults with different cognitive status independently or in combination. The primary objective of the current study was to investigate the clinical utility of ‘two-level’ measurements of RT in discriminating subtypes of NCD using the following approaches: (i) measuring mean RT and intra-individual variability of RT in NCD patients and healthy counterparts; (ii) classifying subtypes of NCD using the two measures of processing speed. We explored the correlations between mean RT, intra-individual variability of RT, and scores on neurocognitive tests

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