Semantic Dementia Diagnosed by F-18 FDG PET/MRI: Co-registered Images
A 61-year-old, right-handed male presented with a sudden change in mental status preceded by a significant decline in functionality over the past 2 years. He was previously a highly functional person and worked as an executive for a Fortune 500 company. His change in mental status was characterized by several behavioral changes; including cruelty toward family members and pets, promiscuity, adultery, drug abuse, wild spending habits, and lack of empathy. His family had also noticed a change in his speech patterns in terms of phonation and pronunciation of words.\nHis initial diagnosis was bipolar disorder; however, he did not respond to mood stabilizing drugs. After losing his job, he was admitted to the psychiatric ward with suicidal tendencies. MRI and magnetic resonance angiography (MRA) were ordered to evaluate for dementia. The MRI [] demonstrated diffuse parenchymal atrophy, which was slightly more extensive in the temporal lobes. There was a lacunar infarct in the right thalamus that was suggestive of vascular dementia. However, the MRA portion was unremarkable and did not support this diagnosis.\nA FDG PET scan was performed the same day for functional metabolic evaluation. The images were co-registered with the MRI using the Institute of Electrical and Electronics Engineers (IEEE) mutual information algorithm.[] The resultant PET/MR images [] demonstrated a pattern of decreased FDG uptake that was predominantly confined to the temporal lobes and was particularly severe in the amygdalae and hippocampi. The decrease in activity was greater on the left side and extended superoposteriorly toward the parietal lobe and Wernicke's area. The other atrophic areas and white matter changes seen on the MRI had intact glucose metabolism. The lacunar infarct also had decreased FDG uptake, but that was considered to be an incidental finding. The decreased glucose metabolism affecting only the temporal lobes (worse on the left side) with the concordant areas of atrophy on the MRI were highly specific for semantic dementia and allowed for a definitive diagnosis to be made.[] Unfortunately, the only management available for this condition is supportive care.