title: How stable are Parkinson's disease subtypes in de novo patients: Analysis of the PPMI cohort?
abstract: To determine the frequency and stability over time of the subgroup characterization of the tremor dominant (TD) versus postural instability gait disorder dominant (PIGD) Parkinson's disease (PD) in de novo patients.
  
  
  
  There is a substantial body of literature on the clinical sub classification of PD into TD versus PIGD subtype. However, there are limited data on the stability of this classification especially in early disease.
  
  
  
  Parkinson's Progression Markers Initiative (PPMI) is a longitudinal case control study of de novo, untreated PD participants at enrollment. Participants undergo a number of assessments including the Movement Disorder Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS). TD versus PIGD subtype was defined based on the previously published formula. We report one-year analysis data.
  
  
  
  320 of 423 PD recruited subjects had data on subtype classification at year 1 and were included in the analysis. 228 (71%) were classified as TD, 56 (18%) as PIGD and 36 (11%) as indeterminate at baseline. At 12 months, 39% PIGD and 18% TD shifted subtypes: 29% PIGD shifted to TD and 11% to Indeterminate; 10% TD shifted to PIGD and 8% to Indeterminate. The classification was not affected by the dopaminergic treatment (p = 0.59).
  
  
  
  TD versus PIGD subtype classification has substantial variability over first year in PD de novo cohort specifically for PIGD subtype. Dopaminergic therapy does not impact the change of the PD subtype. This instability has to be taken into consideration specifically when establishing correlations with the biomarkers and for long term prognostication.
authors.affiliation: Northwestern University Feinberg School of Medicine, United States. Electronic address: tsimuni@nmff.org.
authors.forename: Tanya
authors.initials: T
authors.lastname: Simuni
authors.affiliation: The University of Iowa, United States. Electronic address: chelsea-caspell@uiowa.edu.
authors.forename: Chelsea
authors.initials: C
authors.lastname: Caspell-Garcia
authors.affiliation: The University of Iowa, United States. Electronic address: christopher-coffey@uiowa.edu.
authors.forename: Christopher
authors.initials: C
authors.lastname: Coffey
authors.affiliation: Institute for Neurodegenerative Disorders, United States. Electronic address: slasch@mnimaging.com.
authors.forename: Shirley
authors.initials: S
authors.lastname: Lasch
authors.affiliation: University of California San Francisco, United States. Electronic address: caroline.tanner@ucsf.edu.
authors.forename: Caroline
authors.initials: C
authors.lastname: Tanner
authors.affiliation: Institute for Neurodegenerative Disorders, United States. Electronic address: kmarek@mnimaging.com.
authors.forename: Ken
authors.initials: K
authors.lastname: Marek
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D005260:Female; D020233:Gait Disorders, Neurologic / Q000209:etiology / Q000503:physiopathology*; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000145:classification* / Q000150:complications / Q000503:physiopathology*; D014202:Tremor / Q000209:etiology / Q000503:physiopathology*
keywords: Disease subtypes; Gait disorder predominant; Parkinson's disease; Postural instability; Tremor dominant