title: "Atypical" atypical parkinsonism: Critical appraisal of a cohort.
abstract: Atypical parkinsonian conditions such as multiple system atrophy (MSA), progressive supranuclear palsy (PSP), corticobasal syndrome (CBS) and Dementia with Lewy bodies (DLB) comprise 10-15% of parkinsonian syndromes. Misdiagnosis with Parkinson disease (PD) and within the entities is common, given the absence of reliable biomarkers. However a correct diagnosis is not only important in clinical practice, but also crucial for any trial attempting to identify biomarkers or new treatments.
  
  
  
  Consecutive patients, who were referred to our tertiary center with a diagnosis of a particular AP were included and the medical records were reviewed retrospectively. We applied each set of current diagnostic research criteria to the respective cohort to see which features fit in and if there are any additional atypical features "outside" the classic definition.
  
  
  
  Sixty-nine patients were recruited between January 2013 and May 2015 clinically presenting with one of the following phenotypes: 14 MSA, 24 PSP, 19 CBS and 12 DLB. Up to 49% showed additional "atypical" features and approximately 10% eventually received an alternative diagnosis, in half of whom this being based on genetic testing.
  
  
  
  In a subset of our patients, despite the final diagnosis of an AP being maintained, there were additional "atypical" features. It remains to be seen if these reflect the clinical heterogeneity of APs, or should prompt a search for an alternative diagnosis. The search for biomarkers is more likely to be successful in homogenous groups of "typical" patients, hence the importance of recognizing "atypical" features.
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, WC1N 3BG London, United Kingdom.
authors.forename: Stephanie T
authors.initials: ST
authors.lastname: Hirschbichler
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, WC1N 3BG London, United Kingdom; Dipartimento di Scienze Neurologiche e del Movimento, Università di Verona, Verona, Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Erro
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, WC1N 3BG London, United Kingdom; Department of Neurology, University Medical Center Hamburg-Eppendorf (UKE), Hamburg, Germany.
authors.forename: Christos
authors.initials: C
authors.lastname: Ganos
authors.affiliation: Second Department of Neurology, Attiko Hospital, University of Athens, Greece.
authors.forename: Maria
authors.initials: M
authors.lastname: Stamelou
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, WC1N 3BG London, United Kingdom.
authors.forename: Amit
authors.initials: A
authors.lastname: Batla
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, WC1N 3BG London, United Kingdom; Department of Neurology, University Hospital Heidelberg, Heidelberg, Germany.
authors.forename: Bettina
authors.initials: B
authors.lastname: Balint
authors.affiliation: Sobell Department of Motor Neuroscience and Movement Disorders, UCL Institute of Neurology, WC1N 3BG London, United Kingdom. Electronic address: kbhatia@ucl.ac.uk.
authors.forename: Kailash P
authors.initials: KP
authors.lastname: Bhatia
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003937:Diagnosis, Differential; D005260:Female; D006801:Humans; D020961:Lewy Body Disease / Q000175:diagnosis* / Q000235:genetics; D008297:Male; D008875:Middle Aged; D019578:Multiple System Atrophy / Q000175:diagnosis* / Q000235:genetics; D020734:Parkinsonian Disorders / Q000175:diagnosis* / Q000235:genetics; D013494:Supranuclear Palsy, Progressive / Q000175:diagnosis* / Q000235:genetics
keywords: AP-Phenocopies; Atypical parkinsonism; Corticobasal degeneration; Dementia with lewy bodies; Diagnostic research criteria; Multiple system atrophy; Progressive supranuclear palsy