Diagnostic utility of FDG-PET in the differential diagnosis between different forms of primary progressive aphasia

Abstract

PurposeA joint effort of the European Association of Nuclear Medicine (EANM) and the European Academy of Neurology (EAN) aims at clinical guidance for the use of FDG-PET in neurodegenerative diseases. This paper addresses the diagnostic utility of FDG-PET over clinical/neuropsychological assessment in the differentiation of the three forms of primary progressive aphasia (PPA).MethodsSeven panelists were appointed by the EANM and EAN and a literature search was performed by using harmonized PICO (Population, Intervention, Comparison, Outcome) question keywords. The studies were screened for eligibility, and data extracted to assess their methodological quality. Critical outcomes were accuracy indices in differentiating different PPA clinical forms. Subsequently Delphi rounds were held with the extracted data and quality assessment to reach a consensus based on both literature and expert opinion.ResultsCritical outcomes for this PICO were available in four of the examined papers. The level of formal evidence supporting clinical utility of FDG-PET in differentiating among PPA variants was considered as poor. However, the consensual recommendation was defined on Delphi round I, with six out of seven panelists supporting clinical use.ConclusionsQuantitative evidence demonstrating utility or lack thereof is still missing. Panelists decided consistently to provide interim support for clinical use based on the fact that a typical atrophy or metabolic pattern is needed for PPA according to the diagnostic criteria, and the synaptic failure detected by FDG-PET is an earlier phenomenon than atrophy. Also, a normal FDG-PET points to a non-neurodegenerative cause.

European Association of Nuclear Medicine and European Academy of Neurology recommendations for the use of brain 18F‐fluorodeoxyglucose positron emission tomography in neurodegenerative cognitive impairment and dementia: Delphi consensus

“…The evidence assessment for the 21 literature searches, available at https://drive.google.com/open?id=0B0_ JB3wzTvbpVFYtUGxHdGZWYmc (Data S2), is reported in detail in dedicated review papers [23][24][25][26][27][28][29] and briefly summarized in the pertinent sections below. All panellists filled the whole questionnaire at each of the four rounds.…”

Qualitative and Quantitative Analyses of Brain ¹⁸Fluoro-Deoxy-Glucose Positron Emission Tomography in Primary Progressive Aphasia

“…At QL in 6 of 18 (33.3%) patients (10)(11)(12)(13)(14)(15), the HA were in the frontoparietal and frontotemporal regions with the highest negative z score value at QN, in the prefrontal and temporal regions. However, in the remaining 3 of 18 (16.7%) patients (16)(17)(18) in whom the HA at QL appeared widespread and irregular in both cortical hemispheres, QN localized the highest z score negative value in the prefrontal and parietal areas bilaterally.…”

“…Globally, the combined use of QL and QN evidenced that the two procedures concordantly permitted to achieve a correct diagnosis in 8 of 18 (44.4%) cases, as lvPPA in 4 cases (5)(6)(7)(8) and as nfvPPA in 4 cases (12)(13)(14)(15). In the other 10 of 18 (55.6%) patients, only QN could be useful for the correct diagnosis, as lvPPA in 5 cases (1,2,3,11,16) and as nfvPPA in the remaining 5 cases (4,9,10,17,18). Case 3 is illustrated in Figure 1.…”

“…Brain 18 fluoro-deoxy-glucose positron emission tomography ( 18 F-FDG PET) has also been proposed to ascertain metabolic functional damages in early PPA and define hypometabolism patterns for specific variants [11,14]: frontal lobe in nfvPPA, anterior temporal lobe in svPPA, and temporoparietal lobe in lvPPA. Generally, all patterns predominate in the left hemisphere [15], but in lvPPA, when bilateral, temporoparietal hypometabolism is strongly suggestive of AD progression [16].…”

“…Generally, all patterns predominate in the left hemisphere [15], but in lvPPA, when bilateral, temporoparietal hypometabolism is strongly suggestive of AD progression [16]. Moreover, a high diagnostic accuracy of 18 F-FDG PET in the differential diagnosis of PPA has been reported, especially in nfvPPA; thus, the inclusion of the procedure in PPA diagnostic criteria was suggested, in particular when quantitative (QN) analysis is associated with qualitative (QL) analysis [17,18].…”