title: The pimple sign of progressive supranuclear palsy syndrome.
abstract: BACKGROUND
  Some patients with progressive supranuclear palsy syndrome (PSPS) demonstrate a focal area of midbrain hypometabolism on FDG-PET scans which we call the 'pimple sign'. We assessed its association with midbrain atrophy, its reliability and its ability to differentiate PSPS from corticobasal syndrome (CBS) and multiple system atrophy (MSA).
  
  
  METHODS
  We identified 67 patients with PSPS, CBS or MSA who had volumetric MRI as well as FDG-PET imaging. Midbrain volume was measured and expressed as a percentage of total intracranial volume. Two independent, blinded specialists rated the 'pimple sign' on FDG-PET as 'absent', 'possible' or 'definite'. Midbrain volumes were compared across these groups and reliability assessed with the kappa statistic. Sensitivity and specificity were calculated using CBS and MSA patients as controls.
  
  
  RESULTS
  Midbrain volume was decreased in the 'definite' group compared to the 'absent' and 'possible' groups (p = 0.0036). Inter-rater reliability for the pimple sign was high (κ = 0.90). A 'definite pimple sign' had a high specificity (100%) but low sensitivity (29%) for PSPS, whilst the presence of a possible or definite sign had a sensitivity of 79%.
  
  
  CONCLUSIONS
  The 'pimple sign' of PSPS is associated with midbrain atrophy, and may be helpful in differentiating PSPS from CBS and MSA.
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Hugo
authors.initials: H
authors.lastname: Botha
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Whitwell
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Ajay
authors.initials: A
authors.lastname: Madhaven
authors.affiliation: Department of Information Technology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Matthew L
authors.initials: ML
authors.lastname: Senjem
authors.affiliation: Department of Radiology, Mayo Clinic, Rochester, MN, USA.
authors.forename: Val
authors.initials: V
authors.lastname: Lowe
authors.affiliation: Department of Neurology, Mayo Clinic, Rochester, MN, USA. Electronic address: josephs.keith@mayo.edu.
authors.forename: Keith A
authors.initials: KA
authors.lastname: Josephs
mesh_terms: D000368:Aged; D001284:Atrophy / Q000473:pathology; D005260:Female; D019298:Glucose-6-Phosphate / Q000031:analogs & derivatives; D006801:Humans; D008297:Male; D008636:Mesencephalon / Q000000981:diagnostic imaging* / Q000473:pathology; D008875:Middle Aged; D019578:Multiple System Atrophy / Q000473:pathology; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D012680:Sensitivity and Specificity; D013494:Supranuclear Palsy, Progressive / Q000000981:diagnostic imaging* / Q000473:pathology
chemical_list: D019275:Radiopharmaceuticals; C047515:2-fluoro-2-deoxyglucose-6-phosphate; D019298:Glucose-6-Phosphate
keywords: FDG-PET; Midbrain atrophy; PSPS; Parkinsonism; Pimple sign