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Temporoparietal hypometabolism in frontotemporal lobar degeneration and associated imaging diagnostic errors

  • Author(s): Womack, KB
  • Diaz-Arrastia, R
  • Aizenstein, HJ
  • Arnold, SE
  • Barbas, NR
  • Boeve, BF
  • Clark, CM
  • DeCarli, CS
  • Jagust, WJ
  • Leverenz, JB
  • Peskind, ER
  • Turner, RS
  • Zamrini, EY
  • Heidebrink, JL
  • Burke, JR
  • DeKosky, ST
  • Farlow, MR
  • Gabel, MJ
  • Higdon, R
  • Kawas, CH
  • Koeppe, RA
  • Lipton, AM
  • Foster, NL
  • et al.
Abstract

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). Design: 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. Setting: Academic medical centers. Patients: 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. ©2011 American Medical Association. All rights reserved.

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