Rates of diagnostic transition and cognitive change – an 18-month follow-up of the cohort from the AIBL study

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The April International Psychogeriatrics Article of the Month is entitled ‘Rates of diagnostic transition and cognitive change at 18-month follow-up among 1,112 participants in the Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing (AIBL)’ by Kathryn A. Ellis, Cassandra Szoeke, Ashley I. Bush et al.

The Australian Imaging, Biomarkers and Lifestyle (AIBL) Flagship Study of Ageing is a prospective study of 1,112 individuals (211 with Alzheimer’s disease (AD), 133 with mild cognitive impairment (MCI), and 768 healthy controls (HCs)).

In this paper, the authors report diagnostic and cognitive findings at the first (18-month) follow-up of the cohort. The first aim was to look at rates of transition from HC to MCI, and MCI to AD. The second aim was to characterize the cognitive profiles of individuals who transitioned to a more severe disease stage compared with those who did not.

Eighteen months after baseline, participants underwent comprehensive cognitive testing and diagnostic review, provided an 80 ml blood sample, and completed health and lifestyle questionnaires. A subgroup also underwent amyloid PET and MRI neuroimaging.

The diagnostic status of 90% of the cohorts was determined (972 were reassessed, 28 had died, and 112 did not return for reassessment). The 18-month cohort comprised 692 HCs, 82 MCI cases, 197 AD patients, and one Parkinson’s disease dementia case. The transition rate from HC to MCI was 2.5%, and cognitive decline in HCs who transitioned to MCI was greatest in memory and naming domains compared to HCs who remained stable. The transition rate from MCI to AD was 30.5%.

Cognitive decline with age is not a rapid process for most people, and 18 months is a fairly short period over which to detect emergent decline or transition to clinically diagnosable MCI or AD among previously healthy individuals. Nevertheless, the detailed cognitive data collected in the AIBL study give us the best possible opportunity of detecting such changes that, after future waves of follow-up are complete, may allow us to make a major contribution to determining factors that may be predictive of future cognitive decline in older individuals who are cognitively healthy at present.

The author of the commentary paper, John O’Brien, commented “Of particular note, the AIBL cohort predominantly focuses on the early transition from normality to cognitive impairment, as around three quarters of the participants in the cohort are healthy controls. It also provides a combination of a comprehensive and longitudinal clinical and biomarker assessment with a focus on prior lifestyle factors such as diet and exercise.

There are several extremely interesting and important observations from this study, which have relevance for all cohort studies.Clearly, the combination of clinical, cognitive, risk factor, and biomarker data from the AIBL cohort will help provide some answers to several current questions about the key factors associated with cognitive decline and the rate and temporal ordering of clinical and biomarker changes. However, challenges still remain; even cohorts as sizeable as the AIBL study are relatively limited in size (partly because of the great expense of undertaking such longitudinal deep phenotyping studies) to fully address the investigation of all interactions between environmental, genetic, and lifestyle risk factors. Increased collaborative efforts both nationally and internationally are emerging and will be essential to make future progress.

 

The full paper “Rates of diagnostic transition and cognitive change at 18-month follow-up among 1,112 participants in the Australian Imaging, Biomarkers and Lifestyle Flagship Study of Ageing (AIBL)” is available free of charge for a  limited time here.

The commentary on the paper, “The importance of longitudinal cohort studies in understanding risk and protective factors for dementia” is also available free of charge for one month here.

 

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