Which lobes of the brain are primarily affected by atrophy in Frontotemporal Dementia (FTD)?

Atrophy Patterns in Frontotemporal Dementia (FTD)

Frontotemporal dementia (FTD) predominantly affects the frontal and temporal lobes of the brain, with characteristic "knifelike gyri" atrophy patterns that are typically seen in advanced cases. 1

Primary Regions Affected by Atrophy in FTD

• Frontal lobes show significant atrophy, which is a hallmark feature of FTD 1
• Temporal lobes demonstrate prominent atrophy, often asymmetrically 1
• The orbitofrontal cortex is frequently one of the earliest and most severely affected regions in behavioral variant FTD 2
• Anterior temporal lobes show asymmetric involvement, particularly in language variants 1

Subtype-Specific Atrophy Patterns

Behavioral Variant FTD (bvFTD)

• Demonstrates asymmetric involvement of the anterior temporal lobes 1
• Affects prefrontal cortices, with orbitofrontal regions showing earliest changes 1, 2
• Involves the insula, anterior cingulate, striatum, and thalamus 1
• Shows bilateral cerebellar white matter changes that are more extensive than in other FTD subtypes 3

Primary Progressive Aphasia (PPA) Variants

• Demonstrates asymmetric anteroinferior temporal lobe atrophy, typically worse on the left than the right 1
• Left anterior temporal lobe (ATL) atrophy manifests with naming, word comprehension, reading, and object semantic deficits 4
• Right ATL atrophy presents with impairments of socioemotional, nonverbal semantic, and person-specific knowledge 4

Progression of Atrophy in FTD

• Early stages may show minimal detectable atrophy on standard imaging 2
• Intermediate stages typically show orbitofrontal atrophy bilaterally before other regions 2
• Advanced stages demonstrate widespread frontal and temporal atrophy 5, 2
• The amygdala and hippocampus are severely atrophic by stage 2 of the disease, suggesting they are among the earliest affected areas 5

Imaging Characteristics

• Structural brain MRI without IV contrast is the preferred imaging modality for visualizing atrophy patterns 1
• FDG-PET/CT shows asymmetric hypometabolism in the frontal and temporal lobes, with sparing of the precuneus and occipital lobes 1
• Brain perfusion SPECT demonstrates bilateral anterior brain hypoperfusion 1
• Advanced imaging techniques like diffusion tensor imaging can demonstrate high sensitivity for assessing white matter damage in FTD 1

Clinical Correlation

• Behavioral changes including disinhibition, apathy, and loss of empathy correlate with frontal lobe atrophy 6
• Language deficits correlate with left temporal lobe involvement 4, 7
• Social cognition deficits are associated with right temporal lobe atrophy 4
• Executive function deficits correlate with frontal lobe involvement 7

Differential Diagnostic Features

• FTD shows relative sparing of the parietal lobes, precuneus, and occipital lobes, which helps differentiate it from Alzheimer's disease 1
• MRI perfusion with arterial spin labeling shows bilateral frontal hypoperfusion in FTD, whereas AD demonstrates hypoperfusion in the parietal and posterior cingulate regions 1
• FTD patients have lower NAA/Cr ratios than patients with DLB in the posterior cingulate gyri 1