Clinical Report: Cortical Asymmetry Index Differentiates Dementia Subtypes

Overview

This study introduces the Cortical Asymmetry Index (CAI), derived from information theory applied to cortical thickness measures, as a novel tool to differentiate frontotemporal dementia (FTD) subtypes and Alzheimer's disease (AD). The CAI shows promise for early differential diagnosis, tracking disease progression, and correlating with fluid biomarkers and cognitive measures.

Background

Frontotemporal dementia (FTD) is a heterogeneous neurodegenerative disorder characterized by frontal and temporal lobe atrophy and often misdiagnosed as Alzheimer's disease (AD), especially in younger patients. Differentiating FTD subtypes such as behavioural variant FTD (bvFTD), semantic variant primary progressive aphasia (svPPA), and nonfluent variant primary progressive aphasia (nfvPPA) from AD remains challenging. Cortical asymmetry patterns, measurable via structural MRI, have been associated with these clinical phenotypes. The study proposes a probability distribution-based Cortical Asymmetry Index (CAI) to improve diagnostic accuracy and monitor neurodegeneration.

Data Highlights

Key Findings

• The Cortical Asymmetry Index (CAI), based on information theory and cortical thickness, effectively differentiates FTD from AD and distinguishes FTD subtypes.
• svPPA exhibits the highest cortical asymmetry among FTD phenotypes, consistent with previous visual inspection studies.
• Longitudinal MRI data reveal that CAI can track progression of cortical asymmetry over time in dementia patients.
• CAI correlates with fluid biomarkers such as CSF neurofilament-light chain and plasma markers, as well as cognitive measures including the Mini-Mental State Examination (MMSE).
• Probability distribution-based CAI offers robustness to variability and outliers compared to traditional arithmetic asymmetry measures.
• Clinical and demographic data confirm significant differences in biomarker profiles and cognitive status between AD, FTD, and control groups.

Clinical Implications

The CAI provides clinicians with a quantitative, MRI-based biomarker to improve differential diagnosis between AD and FTD subtypes, potentially reducing misdiagnosis. Its ability to track disease progression longitudinally and correlate with fluid biomarkers supports its use in monitoring therapeutic response and disease evolution. Incorporating CAI into clinical workflows may enhance early detection and personalized management of dementia.

Conclusion

The Cortical Asymmetry Index is a promising tool for distinguishing dementia subtypes and monitoring neurodegeneration, offering improved diagnostic accuracy and clinical utility in managing AD and FTD. Further validation may establish CAI as a standard biomarker in dementia care.

References

1. Rascovsky et al. 2011 -- Diagnostic criteria for behavioural variant frontotemporal dementia
2. Gorno-Tempini et al. 2011 -- Classification of primary progressive aphasia variants
3. National Institute on Aging/Alzheimer’s Association Research Framework 2018 -- Biomarker-based diagnosis of AD
4. Various authors 2014-2023 -- Studies on cortical asymmetry in neurodegeneration