Temporoparietal hypometabolism in frontotemporal lobar degeneration and associated imaging diagnostic errors.
OBJECTIVE
To evaluate the cause of diagnostic errors in the visual interpretation of positron emission tomographic scans with fludeoxyglucose F 18 (FDG-PET) in patients with frontotemporal lobar degeneration (FTLD) and patients with Alzheimer disease (AD).


METHODS
Twelve trained raters unaware of clinical and autopsy information independently reviewed FDG-PET scans and provided their diagnostic impression and confidence of either FTLD or AD. Six of these raters also recorded whether metabolism appeared normal or abnormal in 5 predefined brain regions in each hemisphere-frontal cortex, anterior cingulate cortex, anterior temporal cortex, temporoparietal cortex, and posterior cingulate cortex. Results were compared with neuropathological diagnoses.


METHODS
Academic medical centers.


METHODS
Forty-five patients with pathologically confirmed FTLD (n=14) or AD (n=31).


RESULTS
Raters had a high degree of diagnostic accuracy in the interpretation of FDG-PET scans; however, raters consistently found some scans more difficult to interpret than others. Unanimity of diagnosis among the raters was more frequent in patients with AD (27 of 31 patients [87%]) than in patients with FTLD (7 of 14 patients [50%]) (P=.02). Disagreements in interpretation of scans in patients with FTLD largely occurred when there was temporoparietal hypometabolism, which was present in 7 of the 14 FTLD scans and 6 of the 7 scans lacking unanimity. Hypometabolism of anterior cingulate and anterior temporal regions had higher specificities and positive likelihood ratios for FTLD than temporoparietal hypometabolism had for AD.


CONCLUSIONS
Temporoparietal hypometabolism in FTLD is common and may cause inaccurate interpretation of FDG-PET scans. An interpretation paradigm that focuses on the absence of hypometabolism in regions typically affected in AD before considering FTLD is likely to misclassify a significant portion of FTLD scans. Anterior cingulate and/or anterior temporal hypometabolism indicates a high likelihood of FTLD, even when temporoparietal hypometabolism is present. Ultimately, the accurate interpretation of FDG-PET scans in patients with dementia cannot rest on the presence or absence of a single region of hypometabolism but rather must take into account the relative hypometabolism of all brain regions.
Department of Neurology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Blvd, Dallas, TX 75390-9129, USA. kyle.womack@utsouthwestern.edu
Kyle B
KB
Womack
Ramon
R
Diaz-Arrastia
Howard J
HJ
Aizenstein
Steven E
SE
Arnold
Nancy R
NR
Barbas
Bradley F
BF
Boeve
Christopher M
CM
Clark
Charles S
CS
DeCarli
William J
WJ
Jagust
James B
JB
Leverenz
Elaine R
ER
Peskind
R Scott
RS
Turner
Edward Y
EY
Zamrini
Judith L
JL
Heidebrink
James R
JR
Burke
Steven T
ST
DeKosky
Martin R
MR
Farlow
Matthew J
MJ
Gabel
Roger
R
Higdon
Claudia H
CH
Kawas
Robert A
RA
Koeppe
Anne M
AM
Lipton
Norman L
NL
Foster
D000328:Adult; D017668:Age of Onset; D000368:Aged; D000544:Alzheimer Disease / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology; D001921:Brain / Q000473:pathology; D003937:Diagnosis, Differential; D003951:Diagnostic Errors; D005260:Female; D019788:Fluorodeoxyglucose F18; D057174:Frontotemporal Lobar Degeneration / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D015588:Observer Variation; D010296:Parietal Lobe / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D013702:Temporal Lobe / Q000000981:diagnostic imaging* / Q000378:metabolism* / Q000473:pathology
D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18