title: Side-of-onset of Parkinson's disease in relation to neuropsychological measures.
abstract: BACKGROUND
  Parkinson's disease (PD) usually emerges with a unilateral side-of-onset (left-onset: LOPD; right-onset: ROPD; Marinus & van Hilten, 2015) due to an asymmetrical degeneration of striatal dopaminergic neurons (Donnemiller et al.,Brain, 135, 2012, 3348). This has led to a body of research exploring the cognitive, neuropsychological, and clinical differences between LOPD and ROPD (e.g., Verreyt et al.,Neuropsychology Review, 21, 2011, 405).
  
  
  METHODS
  Thirty ROPD and 14 LOPD cases were drawn from a Boston clinic specializing in PD. Various cognitive and neuropsychological measures were used in an attempt to discover if there were indeed any differences between LOPD and ROPD in this cohort.
  
  
  RESULTS
  For LOPD, duration of illness was found to be significantly greater than that of ROPD. However, further testing was able to confirm that despite this difference, it was not the cause of the other significant differences found. Furthermore, this increased duration was consistent with a previous study (Munhoz et al.,Parkinsonism and Related Disorders, 19, 2013, 77). Performance on the Digit Span Backward (DSB) was found to be significantly poorer in LOPD than ROPD, suggesting compromised executive function in LOPD. Additionally, LOPD had significantly greater anxiety on the DASS Anxiety scales than ROPD. However, unlike Foster et al (Cognitive and Behavioral Neurology, 23, 2010, 4), this increased anxiety could not account for the poorer performance on the DSB for LOPD. Finally, ROPD had significantly greater magical ideation than LOPD, which can be explained by the theory put forth by Brugger and Graves (European Archives of Psychiatry, 247, 1997, 55).
  
  
  CONCLUSIONS
  Clear and significant differences between LOPD and ROPD were found within our cohort. LOPD showed greater impairment of working memory, greater anxiety, and greater duration of illness-all independent of one another; whereas, those with ROPD had greater magical ideation, also independent of any other variables.
authors.affiliation: Department of Neurology Boston University School of Medicine Boston MA USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Modestino
authors.affiliation: Department of Neurology Boston University School of Medicine Boston MA USA.
authors.forename: Chioma
authors.initials: C
authors.lastname: Amenechi
authors.affiliation: Department of Neurology Boston University School of Medicine Boston MA USA.
authors.forename: AnnaMarie
authors.initials: A
authors.lastname: Reinhofer
authors.affiliation: Department of Neurology Boston University School of Medicine Boston MA USA.
authors.forename: Patrick
authors.initials: P
authors.lastname: O'Toole
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001007:Anxiety / Q000503:physiopathology*; D060825:Cognitive Dysfunction / Q000209:etiology / Q000503:physiopathology*; D015331:Cohort Studies; D056344:Executive Function / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D008875:Middle Aged; D009483:Neuropsychological Tests; D010300:Parkinson Disease / Q000150:complications / Q000503:physiopathology*
keywords: Parkinson's disease; Side‐of‐onset; cognitive; neuropsychology