Auditory cortical activity in amnestic mild cognitive impairment: relationship to subtype and conversion to dementia

E J Golob,A Starr,R Irimajiri

doi:10.1093/brain/awl375

Abstract

Mild cognitive impairment (MCI) patients have a high risk of converting to Alzheimer's disease. The most common diagnostic subtypes of MCI have an episodic memory disorder (amnestic MCI) occurring either alone [single domain (SD)] or with other cognitive impairments [multiple domain (MD)]. Previous studies report increased amplitudes of auditory cortical potentials in MCI, but their relationships to MCI subtypes and clinical outcomes were not defined. We studied subjects with amnestic MCI (n = 41: 28 SD, 13 MD), Alzheimer's disease (n = 14), and both younger (n = 22) and age-matched older controls (n = 44). Baseline auditory sensory (P50, N100) and cognitive potentials (P300) were recorded during an auditory discrimination task. MCI patients were followed for up to 5 years, and outcomes were classified as (i) continued diagnosis of MCI (MCI-stable, n = 16), (ii) probable Alzheimer's disease (MCI-convert, n = 18), or other outcomes (n = 7). Auditory potentials were analysed as a function of MCI diagnosis and outcomes, and compared with young, older controls, and mild Alzheimer's disease subjects. P50 amplitude increased with normal ageing, and had additional increases in MCI as a function of both initial diagnosis (MD > than SD) and outcome (MCI-convert > MCI-stable). P300 latency increased with normal ageing, and had additional increases in MCI but did not differ among outcomes. We conclude that auditory cortical sensory potentials differ among amnestic MCI subtypes and outcomes occurring up to 5 years later.

Highlights

Mild cognitive impairment (MCI) is a disorder in older patients that is initially characterized by cognitive decline, such as episodic memory or language function (Flicker et al, 1991; Petersen et al, 2001)
Results in MCI subjects showed that baseline measures of an auditory cortical sensory potential (P50) differed as a function of MCI diagnostic subgroup (SD versus multiple domain (MD)), and outcome
For diagnostic subgroup P50 amplitudes relative to age-matched controls were significantly larger in MCI-MD but not MCI-single domain (SD)

Summary

Introduction

Mild cognitive impairment (MCI) is a disorder in older patients that is initially characterized by cognitive decline, such as episodic memory or language function (Flicker et al, 1991; Petersen et al, 2001). The diagnosis of MCI has been refined by introducing subtypes based on the presence or absence of an episodic memory disorder (amnestic, non-amnestic) and the number of affected cognitive domains (single domain, SD; multiple domain, MD) (Winblad et al, 2004). In the context of amnestic MCI the MCI-SD subtype indicates a relatively selective episodic memory impairment, in contrast to the MCI-MD subtype, which indicates substantial deficits in at least one other cognitive domain. The main difference between MCI-MD and mild dementia is that MCI-MD

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Results

Conclusion