18F-FDG PET Improves Diagnosis in Patients with Focal-Onset Dementias

Alzheimer disease is the cause of up to one-third of cases of primary progressive aphasia or corticobasal syndrome. The primary objective of this study was to determine the accuracy of F-18-FDG PET metabolic imaging for the detection of Alzheimer disease in patients with primary progressive aphasia or corticobasal syndrome. Methods: A cohort of patients (n = 94), including those with an expert clinical diagnosis of logopenic (n = 19), nonfluent (n = 16), or semantic (n = 13) variants of primary progressive aphasia, corticobasal syndrome (n = 14), or Alzheimer disease (n = 24), underwent F-18-FDG metabolic and C-11-labeled Pittsburgh compound B (C-11-PiB) amyloid PET brain imaging. F-18-FDG PET scans interpreted with Neurostat and 3D-SSP displays were classified as revealing Alzheimer disease or other by interpreters who were unaware of the clinical assessments and C-11-PiB PET results. C-11-PiB PET imaging was considered to be the diagnostic reference standard, with a threshold standardized uptake value ratio of 1.5 being indicative of Alzheimer disease pathology. To address possible bias from subgroup selection for the Alzheimer disease binary classifier, we calculated both conventional and balanced accuracies. Results: Diagnoses of Alzheimer disease based on F-18-FDG PET resulted in 84% accuracy (both conventional and balanced). In comparison, diagnoses based on clinical assessments resulted in 65% conventional accuracy and 67% balanced accuracy. Conclusion: Brain F-18-FDG PET scans interpreted with Neurostat and 3D-SSP displays accurately detected Alzheimer disease in patients with primary progressive aphasia or corticobasal syndrome as focal-onset dementias. In such diagnostically challenging cohorts, F-18-FDG PET imaging can provide more accurate diagnoses, enabling more appropriate therapy.