Emerging clinical issues and multivariate analyses in PET investigations

Abstract

PET using 18F-2-fluoro-2-deoxy-D-glucose (FDG-PET) has been gradually introduced in the diagnostic clinical criteria of the most prevalent neurodegenerative diseases. Moreover, an increasing amount of literature have shown that the information provided by FDG-PET enhances the sensitivity of standard imaging biomarkers in less frequent disorders in which an early differential diagnosis can be of paramount relevance for patient management and outcome. Therefore emerging uses of FDG-PET may be important in prion diseases, autoimmune encephalitis and amyotrophic lateral sclerosis. Interestingly, FDG-PET findings can also be observed in early phases of these conditions, even in the presence of normal MRI scans. Thalamic hypometabolism is a common finding in sporadic Creutzfeldt-Jacob disease and fatal familiar insomnia patients, with further cortical synaptic dysfunction in the former. Limbic and extra-limbic metabolic abnormalities (more often hypermetabolism) can be observed in autoimmune encephalitis, although specific patterns may be seen within different syndromes associated with antibodies that target neuronal surface or synaptic antigens. FDG-PET shows its usefulness by discriminating patients with amyotrophic lateral sclerosis associated to upper motor neuron onset that evolve in frontotemporal dementia. Besides visual and voxel based image analysis, multivariate analysis as interregional correlation analysis and independent/principal component statistical analysis have been successfully implemented for PET images increasing the accuracy of the discrimination of neurodegenerative diseases. The clinical presentation and current diagnostic criteria of these neurologic disorders as well as the emerging usefulness of FDG-PET in the diagnostic workup are presented and discussed in this review.