PET-CT Pattern Correlates with Dementia with Lewy Bodies (DLB)
The described PET-CT pattern of asymmetrically reduced tracer concentration in the left frontal, temporal, and parietal regions, anterior cingulate gyrus, bilateral thalami, and cerebellar regions most strongly correlates with Dementia with Lewy Bodies (DLB), not a specific "type" of Parkinson's disease. This pattern represents a parkinsonian syndrome with dementia rather than classical Parkinson's disease.
Key Distinguishing Features on PET-CT
The imaging pattern you describe contains several hallmark features of DLB:
Temporal, parietal, and cerebellar hypometabolism is characteristic of DLB, with the cerebellar involvement being particularly distinctive 1.
Occipital lobe involvement (which may be implied by the posterior distribution) is a distinguishing feature that separates DLB from Alzheimer's disease, where occipital hypometabolism is typically absent 1.
Bilateral thalamic involvement aligns with the subcortical pathology seen in DLB and other Lewy body disorders 1.
Critical Diagnostic Consideration: The Anterior Cingulate Pattern
The anterior cingulate gyrus involvement you describe is important but requires clarification:
If the posterior cingulate is relatively preserved compared to other regions (the "cingulate island sign"), this strongly supports DLB over Alzheimer's disease 1, 2.
The cingulate island sign (preservation of FDG metabolism in the posterior cingulate gyrus) is a specific biomarker for DLB with high specificity, and its presence is associated with preserved memory and processing speed 1.
In contrast, Alzheimer's disease typically shows hypometabolism in the posterior cingulate and precuneus 1.
DLB vs. Parkinson's Disease Dementia
This is DLB rather than Parkinson's disease with dementia based on the clinical rule:
DLB is diagnosed when dementia occurs within 12 months of motor symptom onset 3.
Parkinson's disease dementia (PDD) is diagnosed when dementia develops more than 12 months after established motor symptoms 3.
Both conditions share similar pathology (alpha-synuclein-positive Lewy bodies) but differ in clinical presentation timing 4, 3.
Confirmatory Testing Recommendations
To solidify the diagnosis of DLB:
Dopamine transporter (DaT) SPECT imaging should be performed to assess nigrostriatal dopaminergic degeneration, which shows reduced striatal uptake with 78% sensitivity and 90% specificity for differentiating DLB from Alzheimer's disease 5, 6.
A normal DaT scan shows symmetric comma-shaped uptake in caudate nuclei and putamina; loss of this pattern with reduced putaminal uptake indicates dopaminergic neuron loss consistent with DLB 5, 6.
The American College of Radiology recommends FDG-PET before DaT scanning for cost considerations, but DaT scanning provides additional diagnostic value when clinical features overlap 5.
Clinical Correlation Required
The imaging findings must be correlated with clinical features of DLB:
Fluctuating cognitive impairment with variations in alertness and attention 4, 3.
Spontaneous recurrent visual hallucinations that are typically well-formed and detailed 4, 3.
Parkinsonism that is usually akineto-rigid without classical rest tremor, and is mild to moderately severe 4, 3.
Visuospatial deficits and frontal executive dysfunction are more prominent than memory impairment early in the disease 4, 3.
Important Pitfall to Avoid
Do not confuse this with frontotemporal dementia (FTD), which can show asymmetric frontal and temporal hypometabolism:
FTD demonstrates bilateral frontal hypoperfusion with sparing of the precuneus and occipital lobes 1.
FTD shows asymmetric involvement of anterior temporal lobes, prefrontal cortices, insula, anterior cingulate, striatum, and thalamus in behavioral variant FTD 1.
However, cerebellar involvement and the pattern of thalamic involvement favor DLB over FTD 1.