The Congruency of Neuropsychological and F18-FDG Brain PET/CT Diagnostics of Alzheimer’s Disease (AD) In Routine Clinical Practice: Insights From a Mixed Neurological Patient Cohort
Authors: Hansen Sascha , Keune Jana , Küfner Kim , Meister Regina , Habich Juliane , Koska Julia , Förster Stefan , Oschmann Patrick , Keune Philipp M. 
Published: June 2021

Abstract
Background:Clinical diagnostics of Alzheimer’s Disease (AD) require a multimodal approach. Neuropsychological assessments are commonly implemented to obtain information about the degree of cognitive impairment, while cerebrospinal fluid markers and imaging data provide etiological information. In routine clinical practice, neuropsychologists often have to rely on relatively limited anamnestic information, as well as cognitive test results and are required to infer whether patients actually suffer from AD, prior to the availability of exhaustive etiological information. To date, it remains to be explored how congruent the results of such a phenomenological approach may be with results from neuroimaging techniques such as FDG-PET/CT examinations. The latter are known to yield highly accurate diagnostic information. Methods:A mixed sample of N=127 hospitalized neurological patients suspected of displaying a syndrome of dementia underwent routine differential diagnostics including an extensive neuropsychological and an FDG-PET/CT examination. The neuropsychological examination included an interview in which anamnestic information was obtained, as well as the administration of the standardized CERAD cognitive test battery. Two separate decisional approaches were considered: First, routine diagnostic results were obtained, as reflected by the final clinical decision of the examining neuropsychologist (ADClinical vs. non-ADClinical) for the routine clinical report. Secondly, a logistic regression model was implemented, that relied on data from the CERAD test profiles alone. Based on the logistic regression, the CERAD test subscales that best predicted the presence of AD according to the FDG-PET/CT results were identified and a nominal categorization was obtained (ADTest vs. non-ADTest). Results from both decisional approaches were matched against the FDG-PET/CT results (ADPET vs. non-ADPET) in cross-tables and estimates of accuracy, sensitivity and specificity were derived.Results:Based on the FDG-PET/CT examination, N=33/127 (26%) of the patients were diagnosed as ADPET patients. When matched against these results, the clinical decision approach of the neuropsychological examination (ADClinical vs. non-ADClinical) yielded a good accuracy (84.2%), involving moderate sensitivity (75.8%) and excellent specificity (92.6%). The decisional approach that relied on the neuropsychological test data alone (ADTest vs. non-ADTest) involved a lower estimate of accuracy (74.8%), that was attributable to considerably decreased sensitivity (56.3%) while specificity was comparable (93.3%) to the clinical decision model.Conclusions:These results indicate that it is feasible to identify AD in context of a comprehensive routine neuropsychological examination in a mixed sample of neurological patients, relative to an FDG-PET/CT classification. However, decisions based on cognitive test results alone appear limited in this respect. It may be assumed that anamnestic information in combination with the clinical impression obtained by the neuropsychological examiner play a crucial role in the identification of AD patients in routine clinical practice.