Clinical Impact of a Second FDG-PET in Atypical/Unclear Dementia Syndromes

J Alzheimers Dis. 2016;49(3):695-705. doi: 10.3233/JAD-150302.


Diagnosis of atypical/unclear dementia is often difficult and this delays treatment initiation. Several authors have shown that beyond standard dementia workup, 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) reduces the number of unclear diagnoses, leads to earlier treatment, and has a beneficial impact on families. However, it is not uncommon that the FDG-PET findings are equivocal in this setting. For those cases, a repeat FDG-PET may clarify the diagnosis and prevent treatment delay. We retrospectively assessed the clinical impact of a repeat FDG-PET in 59 patients with atypical/unclear dementia syndromes and inconclusive initial FDG-PET. Changes in primary diagnosis, diagnostic confidence, and management following the second FDG-PET were examined. Conducting a second FDG-PET reduced the number of unclear diagnoses from 80% to 34% , led to diagnostic change in 24% of cases, and treatment modification in 22% of patients. Overall, the clinical impact was higher when initial diagnostic confidence was low and the second FDG-PET repeated ≥12 months after the first one. In tertiary care memory clinic settings, when diagnostic incertitude persists despite extensive evaluation and an equivocal FDG-PET, repeating the FDG-PET 12 months later can greatly clarify the diagnosis and improve management.

Keywords: Atypical dementia; FDG-PET; brain imaging; differential diagnosis.

MeSH terms

  • Adult
  • Brain / diagnostic imaging*
  • Dementia / diagnosis*
  • Dementia / diagnostic imaging*
  • Diagnosis, Differential
  • Female
  • Fluorodeoxyglucose F18*
  • Humans
  • Male
  • Middle Aged
  • Positron-Emission Tomography / methods*
  • Radiopharmaceuticals
  • Retrospective Studies


  • Radiopharmaceuticals
  • Fluorodeoxyglucose F18