Scintigraphic spectrum of fronto temporal lobar degeneration on FDG PET CT

Abstract

A retrospective analysis of 40 patients of clinically suspected frontotemporal lobar degeneration, presenting with variable degrees of altered behavior, language, executive control and motor symptoms, was done. All the subjects underwent F-18 FDG PET CT scan of the brain and the studies were analyzed both qualitatively (visually) and semi quantitatively. Few of the subjects also underwent dopamine transporter imaging with Tc 99 m TRODAT 1 on a separate day. The subjects were clinically divided into Behavioral variant fronto temporal dementia (FTD), Non fluent/agrammatic variant primary progressive aphasia (PPA), Semantic variant PPA, Logopenic PPA and FTD with motor symptoms. The FDG uptake patterns were recorded and areas of cortical hypometabolism in the cerebral cortex that were two standard deviations from the mean were considered as abnormal. Behavioral variant subjects, showed diffuse hypometabolism in the medial frontal, Orbital frontal, anterior cingulate and fronto-insular cortices. The subjects with non fluent/agrammatic variant PPA showed predominant left posterior fronto-insular hypometabolism. The subjects with Semantic variant PPA revealed predominant anterior temporal hypometabolism, the Logopenic PPA subjects showed hypometabolism around the angular gyrus and the subjects with motor symptoms showed hypometabolism in the sensorimotor cortices. FDG PET scan may act as a non invasive diagnostic modality in differentiating the myriad clinical and pathologic presentation of fronto temporal lobar degeneration and may help in documenting and characterizing the various overlap syndromes thereby helping in prognosticating the disease process.