title: Importance of nondopaminergic features in evaluating disease severity of Parkinson disease.
abstract: OBJECTIVE
  The aim of this study was to explore the role of predominantly nondopaminergic (PND) features in evaluating disease severity and progression of Parkinson disease (PD).
  
  
  METHODS
  Principal component analysis was used on the baseline data of 396 patients to explore consistency of interrelations between important PND domains (cognitive impairment, depressive symptoms, excessive daytime sleepiness, psychotic symptoms, autonomic dysfunction, and postural instability and gait difficulty) across different ranges of disease duration. Hereafter, we evaluated the reliability and validity of a composite score of all PND domains and examined reproducibility of the findings in a large independent cohort.
  
  
  RESULTS
  Principal component analysis revealed a consistent 1-factor solution across groups with different disease durations. Cronbach α of the total group was 0.75 for the PND composite score, and corrected item-total correlations were all above the criterion value of 0.3. Validity of the PND composite score was confirmed by significant positive correlations with Hoehn and Yahr stage, severity of motor symptoms, disease duration, and age. Findings were replicated in the independent cohort.
  
  
  CONCLUSIONS
  Our findings show the robustness of a composite score of PND domains as a measure of disease severity across the disease course of PD. Composite measures of PND domains, which largely are insensitive to dopaminergic medication, may provide a more complete and accurate evaluation of disease severity and progression in PD.
authors.affiliation: From the Department of Neurology (J.F.v.d.H., J.M., J.J.v.H.), Leiden University Medical Center, Leiden, the Netherlands; and Alzheimer Center Reina Sofia Foundation and CIBERNED (P.M.-M.), Carlos III Institute of Health, Madrid, Spain.
authors.forename: Jorine F
authors.initials: JF
authors.lastname: van der Heeden
authors.forename: Johan
authors.initials: J
authors.lastname: Marinus
authors.forename: Pablo
authors.initials: P
authors.lastname: Martinez-Martin
authors.forename: Jacobus J
authors.initials: JJ
authors.lastname: van Hilten
mesh_terms: D000293:Adolescent; D000368:Aged; D002648:Child; D015331:Cohort Studies; D004298:Dopamine / Q000378:metabolism; D059290:Dopaminergic Neurons / Q000378:metabolism / Q000473:pathology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis* / Q000378:metabolism / Q000523:psychology*; D025341:Principal Component Analysis; D012720:Severity of Illness Index; D055815:Young Adult
chemical_list: D004298:Dopamine