MRI Measures of Temporoparietal Atrophy During Prodromal Alzheimer Disease

The featured paper is ‘MRI measures of temporoparietal regions show differential rates of atrophy during prodromal AD’ by Desikan and colleagues.

The authors cite evidence for atrophy of temporoparietal regions in longitudinal studies in people with Mild Cognitive Impairment (MCI) who progress to Alzheimer Disease and this study is a logical progression from these previous findings.

66 people were selected from a larger group of 339 people recruited from the media. The inclusion criteria are not given but instead the reader is referred to another paper. In essence this means that another paper is required for a more detailed appraisal of this study. People were stratified according to their status at entry into the study and subsequent conversion to MCI or probable Alzheimer Disease (AD). The authors state that there was a difference in age between those who converted from MCI to probable AD and those with MCI at baseline and follow-up (non-converters) and that there was no difference in other demographic or genetic variables. Inspection of the table in the appendix revealed a difference of two years between the groups. A 1.5 Tesla scanner was used for image acquisition. The follow-up scan protocol varied between groups. Thus for controls and non-converters comparison occurred at 3 years whilst for those that converted it was as close to the time of confirmed diagnosis as possible. 14 regions of interest were identified from the temporoparietal region and a ‘Free Surfer’ Software package was used for analysis. The authors used published boundary definitions to validate their regions of interest. The authors used the MANOVA to evaluate annual atrophy rates in the regions of interest using the different groups as variables.

There were six regions of interest which were found to differ between converters and non-converters these being

Hippocampus (large effect size)

Temporal Pole (large effect size)

Entorhinal Cortex (large effect size)

Fusiform Gyrus (large effect size)

Middle Temporal Gyrus (large effect size)

Inferior Temporal Gyrus

Interestingly there was no difference between non-converters and controls in regions of interest.

Converters and controls differed in the following regions

Hippocampus (large effect size)

Entorhinal Cortex (large effect size)

Temporal Pole (large effect size)

Middle Temporal Gyrus (large effect size)

Fusiform Gyrus (large effect size)

Inferior Parietal Lobule

The authors found that three areas in particular – hippocampus, temporal pole and entorhinal cortex were particulary effective in disciminating between converters and non-converters and controls. The atrophy rates in these regions were also correlated with clinical severity and the rates for these three regions were aggregated to produce a more effective predictor of conversion. The authors also corrected for age and found that this did not alter the findings for the three regions described above.

The study provides useful evidence of regions that might be implicated in conversion to Alzheimer Disease and which fit with other lines of evidence for pathogenesis. It will be interesting to see if these findings are replicated and the impact that this will have.

STT 3

References

Desikan R, Fischl B, Cabral H, Kemper T, Guttmann C, Blacker D, Hyman B, Albert M and Killiany R. MRI measures of temporoparietal regions show differential rates of atrophy during prodromal AD. Neurology. 2008. 71(11). 819-825.

Disclaimer

The comments made here represent the opinions of the author and do not represent the profession or any body/organisation. The comments made here are not meant as a source of medical advice and those seeking medical advice are advised to consult with their own doctor. The author is not responsible for the contents of any external sites that are linked to in this blog.

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