title: "On" state freezing of gait in Parkinson disease: a paradoxical levodopa-induced complication.
abstract: OBJECTIVE
  To describe the phenotype of levodopa-induced "on" freezing of gait (FOG) in Parkinson disease (PD).
  
  
  METHODS
  We present a diagnostic approach to separate "on" FOG (deterioration during the "on state") from other FOG forms. Four patients with PD with suspected "on" FOG were examined in the "off state" (>12 hours after last medication intake), "on state" (peak effect of usual medication), and "supra-on" state (after intake of at least twice the usual dose).
  
  
  RESULTS
  Patients showed clear "on" FOG, which worsened in a dose-dependent fashion from the "on" to the "supra-on" state. Two patients also demonstrated FOG during the "off state," of lesser magnitude than during "on." In addition, levodopa produced motor blocks in hand and feet movements, while other parkinsonian features improved. None of the patients had cognitive impairment or a predating "off" FOG.
  
  
  CONCLUSIONS
  True "on" FOG exists as a rare phenotype in PD, unassociated with cognitive impairment or a predating "off" FOG. Distinguishing the different FOG subtypes requires a comprehensive motor assessment in at least 3 medication states.
authors.affiliation: UC Neuroscience Institute, Department of Neurology, Gardner Family Center for Parkinson’s Disease and MovementDisorders, University of Cincinnati, Cincinnati, OH, USA. alberto.espay@uc.edu
authors.forename: A J
authors.initials: AJ
authors.lastname: Espay
authors.forename: A
authors.initials: A
authors.lastname: Fasano
authors.forename: B F L
authors.initials: BF
authors.lastname: van Nuenen
authors.forename: M M
authors.initials: MM
authors.lastname: Payne
authors.forename: A H
authors.initials: AH
authors.lastname: Snijders
authors.forename: B R
authors.initials: BR
authors.lastname: Bloem
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000978:Antiparkinson Agents / Q000009:adverse effects* / Q000627:therapeutic use; D001519:Behavior; D005260:Female; D005684:Gait / Q000502:physiology; D020233:Gait Disorders, Neurologic / Q000139:chemically induced / Q000209:etiology*; D006801:Humans; D007980:Levodopa / Q000009:adverse effects* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications* / Q000175:diagnosis; D010641:Phenotype
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa