title: A 12-year population-based study of freezing of gait in Parkinson's disease.
abstract: BACKGROUND
  Freezing of gait (FOG) is a potentially disabling motor problem in Parkinson's disease (PD) with uncertain etiology. Longitudinal studies of FOG in PD are scarce. We determined the prevalence, incidence, and associated clinical risk factors and concomitants of FOG during prospective long-term follow-up of a population-based PD cohort.
  
  
  METHODS
  A community-based prevalent cohort of 232 PD patients was followed prospectively over 12 years. Reassessments were conducted at 4 and 8 years, and then annually. FOG, as well as severity of parkinsonism, motor complications, and psychotic symptoms were assessed by the Unified PD Rating Scale, and cognitive impairment by the Mini-Mental State Examination. Generalized estimating equations were applied to investigate baseline risk factors and concomitants of FOG over time.
  
  
  RESULTS
  The point prevalence of FOG at baseline was 27% (95% confidence interval (95%-CI) 22-33%). By study end, 63% (95%-CI 56-69%) of patients had developed FOG. The incidence rate of FOG was 124.2 (95%-CI 101.5-152.1) per 1000 person-years. Motor fluctuations (odds ratio (OR) 3.45; p = 0.036) and higher levodopa dose (OR 1.30/100 mg, p = 0.009) at baseline were independent risk factors of incident FOG. Prevalent FOG over time was additionally associated with features thought to reflect extrastrial, non-dopaminergic pathologies, including PIGD (postural instability/gait difficulty, OR 6.30/10 points, p < 0.001) and psychosis (OR 1.85; p = 0.016).
  
  
  CONCLUSIONS
  These findings demonstrate that FOG affects the majority of patients in the general PD population and provide support to the hypothesis that alterations in both basal ganglia and extrastriatal brain areas are involved in the pathogenesis of FOG in PD.
authors.affiliation: The Norwegian Centre for Movement Disorders, Stavanger University Hospital, P.O. Box 8100, N-4068 Stavanger, Norway; Department of Neurology, Stavanger University Hospital, P.O. Box 8100, N-4068 Stavanger, Norway. Electronic address: elin.forsaa@sus.no.
authors.forename: E B
authors.initials: EB
authors.lastname: Forsaa
authors.affiliation: The Norwegian Centre for Movement Disorders, Stavanger University Hospital, P.O. Box 8100, N-4068 Stavanger, Norway.
authors.forename: J P
authors.initials: JP
authors.lastname: Larsen
authors.affiliation: Center for Clinical Research, Haukeland University Hospital, P.O. Box 1400, N-5021 Bergen, Norway.
authors.forename: T
authors.initials: T
authors.lastname: Wentzel-Larsen
authors.affiliation: The Norwegian Centre for Movement Disorders, Stavanger University Hospital, P.O. Box 8100, N-4068 Stavanger, Norway; Department of Neurology, Stavanger University Hospital, P.O. Box 8100, N-4068 Stavanger, Norway.
authors.forename: G
authors.initials: G
authors.lastname: Alves
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000978:Antiparkinson Agents / Q000627:therapeutic use; D015331:Cohort Studies; D018672:Community Health Planning; D005260:Female; D046352:Freezing Reaction, Cataleptic / Q000187:drug effects / Q000502:physiology*; D020233:Gait Disorders, Neurologic / Q000453:epidemiology / Q000209:etiology*; D006801:Humans; D007980:Levodopa / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000150:complications* / Q000188:drug therapy / Q000453:epidemiology; D012307:Risk Factors; D012720:Severity of Illness Index
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa
keywords: Course; Freezing of gait; Motor fluctuations; Parkinson's disease; Risk factors