Abstract
Medial temporal lobe (MTL) atrophy is an important morphological marker of many dementias and is closely related to cognitive decline. In this study we aimed to characterize longitudinal progression of MTL atrophy in 93 individuals with subjective cognitive decline and mild cognitive impairment followed up over six years, and to assess if clinical rating scales are able to detect these changes. All MRI images were visually rated according to Scheltens’ scale of medial temporal atrophy (MTA) by two neuroradiologists and AVRA, a software for automated MTA ratings. The images were also segmented using FreeSurfer’s longitudinal pipeline in order to compare the MTA ratings to volumes of the hippocampi and inferior lateral ventricles. We found that MTL atrophy rates increased with CSF biomarker abnormality, used to define preclinical stages of Alzheimer’s Disease. Both AVRA’s and the radiologists’ MTA ratings showed similar longitudinal trends as the subcortical volumes, suggesting that visual rating scales provide a valid alternative to automatic segmentations. Our results further showed that it took more than 8 years on average for individuals with mild cognitive impairment, and an Alzheimer’s disease biomarker profile, to increase the MTA score by one. This suggests that discrete MTA ratings are too coarse for tracking individual MTL atrophy in short time spans. While the MTA scores from each radiologist showed strong correlations to subcortical volumes, the inter-rater agreement was low. We conclude that the main limitation of quantifying MTL atrophy with visual ratings in clinics is the subjectiveness of the assessment.
Highlights
Atrophy of the medial temporal lobe (MTL) is an important diagnostic biomarker in many different dementias, including Alzheimer’s Disease (AD)
Violinplots illustrating the distribution of HC and inferior lateral ventricle (ILV) volumes per Medial Temporal Atrophy (MTA) score and rater are shown in Fig. 2, where we note that Rad. 1 systematically gave higher MTA scores than Rad. 2
All MTL measures showed that the atrophy rates increased with progressing AD CSF pathology, with the exception of the ratings from Rad. 1 that showed a milder progression in the A+T− group
Summary
Atrophy of the medial temporal lobe (MTL) is an important diagnostic biomarker in many different dementias, including Alzheimer’s Disease (AD). In research we quantify atrophy using automatic softwares that compute volume or thickness measures of regions of interests, specified by a neuroanatomical atlas These softwares are either not sufficiently reliable for clinical usage, and the ones that have been approved are not widely implemented. The MTA scale has been shown to reliably distinguish individuals with AD from healthy elderly (Scheltens et al, 1992; Wahlund et al, 1999; Westman et al, 2011) It is an ordinal scale ranging from 0 (no atrophy) to 4 (end-stage atrophy) where an integer score is given for each hemisphere. Several studies have reported on the diagnostic ability and relevant clinical cut-offs of the MTA scale (Westman et al, 2011; Scheltens et al, 1992; Ferreira et al, 2015), and others have argued for the importance of reporting MTA in the clinical routine (Torisson et al, 2015; Håkansson et al, 2019; Wahlund et al, 2017)
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