title: Cortical asymmetry in Parkinson's disease: early susceptibility of the left hemisphere.
abstract: Clinically, Parkinson's disease (PD) presents with asymmetric motor symptoms. The left nigrostriatal system appears more susceptible to early degeneration than the right, and a left-lateralized pattern of early neuropathological changes is also described in several neurodegenerative conditions, including Alzheimer's disease, frontotemporal dementia, and Huntington's disease. In this study, we evaluated hemispheric differences in estimated rates of atrophy in a large, well-characterized cohort of PD patients.
  
  
  
  Our cohort included 205 PD patients who underwent clinical assessments and T1-weighted brain MRI's. Patients were classified into Early (n= 109) and Late stage (n= 96) based on disease duration, defined as greater than or less than 10 years of motor symptoms. Cortical thickness was determined using FreeSurfer, and a bootstrapped linear regression model was used to estimate differences in rates of atrophy between Early and Late patients.
  
  
  
  Our results show that patients classified as Early stage exhibit a greater estimated rate of cortical atrophy in left frontal regions, especially the left insula and olfactory sulcus. This pattern was replicated in left-handed patients, and was not influenced by the degree of motor symptom asymmetry (i.e., left-sided predominant motor symptoms). Patients classified as Late stage exhibited greater atrophy in the bilateral occipital, and right hemisphere-predominant cortical areas.
  
  
  
  We show that cortical degeneration in PD differs between cerebral hemispheres, and findings suggest a pattern of early left, and late right hemisphere with posterior cortical atrophy. Further investigation is warranted to elucidate the underlying mechanisms of this asymmetry and pathologic implications.
authors.affiliation: Department of Neurology Vanderbilt University Nashville TN USA.
authors.forename: Daniel O
authors.initials: DO
authors.lastname: Claassen
authors.affiliation: Department of Neurology Vanderbilt University Nashville TN USA.
authors.forename: Katherine E
authors.initials: KE
authors.lastname: McDonell
authors.affiliation: Vanderbilt University Institute of Imaging Science Nashville TN USA.
authors.forename: Manus
authors.initials: M
authors.lastname: Donahue
authors.affiliation: Meharry Medical College Nashville TN USA.
authors.forename: Shiv
authors.initials: S
authors.lastname: Rawal
authors.affiliation: Department of Neurology Vanderbilt University Nashville TN USA.
authors.forename: Scott A
authors.initials: SA
authors.lastname: Wylie
authors.affiliation: Department of Neurosurgery University of Louisville Louisville KY USA.
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Neimat
authors.affiliation: Department of Biostatistics Vanderbilt University Nashville TN USA.
authors.forename: Hakmook
authors.initials: H
authors.lastname: Kang
authors.affiliation: Department of Neurology Vanderbilt University Nashville TN USA.
authors.forename: Peter
authors.initials: P
authors.lastname: Hedera
authors.affiliation: Department of Psychology Vanderbilt University Nashville TN USA.
authors.forename: David
authors.initials: D
authors.lastname: Zald
authors.affiliation: Department of Electrical Engineering Vanderbilt University Nashville TN USA.
authors.forename: Bennett
authors.initials: B
authors.lastname: Landman
authors.affiliation: Department of Electrical Engineering Vanderbilt University Nashville TN USA.
authors.forename: Benoit
authors.initials: B
authors.lastname: Dawant
authors.affiliation: Vanderbilt University Institute of Imaging Science Nashville TN USA.
authors.forename: Swati
authors.initials: S
authors.lastname: Rane
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001284:Atrophy / Q000000981:diagnostic imaging; D005260:Female; D007839:Functional Laterality / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000473:pathology* / Q000503:physiopathology; D013378:Substantia Nigra / Q000000981:diagnostic imaging / Q000473:pathology*
keywords: MRI; Parkinson's disease; cortex; left hemisphere; neurodegeneration