Abstract
Background
To understand the utility of putative biomarkers for Alzheimer's disease (AD) it is important to understand how cognition and clinical status change as the disease develops.This study aimed to characterise changes in cognition and clinical status from baseline at 18 and 36-month reassessments in the Australian Imaging Biomarkers and Lifestyle (AIBL) study.
Methods
The AIBL inception cohort [1112–211 AD, 133 mild cognitive impairment (MCI) and 768 healthy controls (HCs)] underwent re-assessment 18 and 36-months after enrollment, involving comprehensive cognitive assessment, blood biomarker analysis and health and lifestyle assessment. A subgroup received amyloid imaging (C11- PiB-PET) and MRI.
Results
Retention at 18-months was 89.6 percent [18-month cohort; 317 HC non-memory complainers (NMC), 374 HC subjective memory complainers (SMC), 81 MCI and 197 AD patients] and 77.9 percent at 36-months [36-month cohort; 301 NMC, 310 SMC, 58 MCI, 154 AD and 4 non-AD dementia]. SMC status, derived by a single question, as an unstable categorisation at both follow-ups (18-months; 30% changed from NMC to S MC, 24% from SMC to NMC; at 36-months 20% from NMC to SMC, 21% SMC to NMC). Baseline mood measures differentiated NMC and SMC, however they did not differ in cognitive change over the initial 18 months. Conversion from HC to MCI at 18-months was 2.3 percent, and 3.6 percent by 36-months, with 69 percent of converters previously being SMC. HC who converted to MCI over the initial 18 months showed greater decline on learning, short-term and long-term memory than HC whose clinical status remained stable. Conversion from MCI to AD was 24 percent at 18 months and 36 percent by 36 months. Higher CDR sum-of-boxes and lower episodic memory scores predicted MCI conversion to AD by the 18-month assessment. Individuals with MCI at baseline who did not convert to AD at the 18-month re-assessment showed no change in any aspect of cognition.
Conclusions
Rates of conversion from healthy to MCI and from MCI to AD were consistent with established estimates. Cognitive scores at baseline and patterns of change over 18 months differ for individuals who change clinical categories to those who remain stable. This cohort provides a platform to examine putative biomarkers for AD.