OBJECTIVE: Differentiating Parkinson's disease (PD) from atypical parkinsonian disorders (APD) such as Multiple System Atrophy, parkinsonian type (MSA-p) or Progressive Supranuclear Palsy (PSP-RS) can be challenging. Early signs of postural Instability and gait disability (PIGD) are considered clues that may signal presence of APD. However, it remains unknown which PIGD test - or combination of tests - can best distinguish PD from APD. We evaluated the discriminative value of several widely-used PIGD tests, and aimed to develop a short PIGD evaluation that can discriminate parkinsonian disorders. METHODS: In this multicentre cohort study patients were recruited by 11 European MSA Study sites. Patients were diagnosed using standardized criteria. Postural instability and gait disability was evaluated using interviews and several clinical tests. RESULTS: Nineteen PD, 21 MSA-p and 25 PSP-RS patients were recruited. PIGD was more common in APD compared to PD. There was no significant difference in axial symptoms between PSP-RS and MSA-p, except for self-reported falls (more frequent in PSP-RS patients). The test with the greatest discriminative power to distinguish APD from PD was the ability to perform tandem gait (AUC 0.83; 95% CI 71-94; p < 0.001), followed by the retropulsion test (AUC 0.8; 95% CI 0.69-0.91; p < 0.001) and timed-up-and-go test (TUG) (AUC 0.77; 95% CI 0.64-0.9; p = 0.001). The combination of these three tests yielded highest diagnostic accuracy (AUC 0.96; 95% CI 0.92-1.0; p < 0.001). CONCLUSIONS: Our study suggests that simple "bedside" PIGD tests - particularly the combination of tandem gait performance, TUG and retropulsion test - can discriminate APD from PD.

Centre for Neurodegenerative Diseases Department of Medicine and Surgery University of Salerno Italy

Department of Neurology and Centre of Clinical Neuroscience Charles University Prague Czech Republic

Department of Neurology Medical University Innsbruck Austria

Department of Neurology Parkinson Centre Milano Italy

Department of Neurology Rabin Medical Centre Petach Tiqva Israel

Department of Neurology University Hospital Aarhus Denmark

Institute of Neurology Clinical Centre of Serbia Belgrade Serbia

Institute of Neurology Clinical Centre of Serbia Belgrade Serbia; Faculty of Medicine University of Belgrade Belgrade Serbia

IRCCS Institute of Neurological Sciences of Bologna and Department of Biomedical and Neuromotor Sciences University of Bologna Bologna Italy

Neurological Institute Tel Aviv Sourasky Medical Centre Tel Aviv Israel

Neurology Service Hospital Clínic Universitari Institut d'Investigacions Biomèdiques August Pi i Sunyer Barcelona Spain

Radboud University Medical Centre Donders Institute for Brain Cognition and Behaviour Department of Neurology Parkinson Centre Nijmegen Nijmegen The Netherlands

Radboud University Medical Centre Donders Institute for Brain Cognition and Behaviour Department of Rehabilitation The Netherlands

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