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Distinguishing SWEDDs patients with asymmetric resting tremor from Parkinson's disease: A clinical and electrophysiological study

Authors

  • Petra Schwingenschuh MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
    2. Department of Neurology, Medical University Graz, Graz, Austria
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  • Diane Ruge MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • Mark J. Edwards PhD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • Carmen Terranova MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • Petra Katschnig MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
    2. Department of Neurology, Medical University Graz, Graz, Austria
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  • Fatima Carrillo MD,

    1. Unidad de Trastornos del Movimiento, Servicio de Neurología, Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, CIBERNED, Seville, Spain
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  • Laura Silveira-Moriyama MD,

    1. Reta Lila Weston Institute of Neurological Studies, UCL, Institute of Neurology, London, United Kingdom
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  • Susanne A Schneider PhD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • Georg Kägi MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • Francisco J Palomar MD,

    1. Unidad de Trastornos del Movimiento, Servicio de Neurología, Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, CIBERNED, Seville, Spain
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  • Penelope Talelli MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • John Dickson PhD,

    1. Institute of Nuclear Medicine, UCL, London, United Kingdom
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  • Andrew J. Lees MD,

    1. Reta Lila Weston Institute of Neurological Studies, UCL, Institute of Neurology, London, United Kingdom
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  • Niall Quinn MD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • Pablo Mir PhD,

    1. Unidad de Trastornos del Movimiento, Servicio de Neurología, Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío/CSIC/Universidad de Sevilla, CIBERNED, Seville, Spain
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  • John C. Rothwell PhD,

    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
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  • Kailash P. Bhatia MD

    Corresponding author
    1. Sobell Department of Motor Neuroscience and Movement Disorders, Institute of Neurology, UCL, Queen Square, London, United Kingdom
    • Sobell Department, Institute of Neurology, UCL, Queen Square, London WC1N 3BG, United Kingdom
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  • Potential conflict of interest: nothing to report.

Abstract

Approximately 10% of patients diagnosed clinically with early Parkinson's disease (PD) have normal dopaminergic functional imaging (Scans Without Evidence of Dopaminergic Deficit [SWEDDs]). An important subgroup of SWEDDs are those with asymmetric rest tremor resembling parkinsonian tremor. Clinical and pathophysiological features which could help to distinguish SWEDDs from PD have not been explored. We therefore studied clinical details including non-motor symptoms in 25 tremulous SWEDDs patients in comparison to 25 tremor-dominant PD patients. Blinded video rating was used to compare examination findings. Electrophysiological tremor parameters and also response to a cortical plasticity protocol using paired associative stimulation (PAS) was studied in 9 patients with SWEDDs, 9 with tremor-dominant PD (with abnormal dopamine transporter single photon emission computed tomography findings), 8 with segmental dystonia, and 8 with essential tremor (ET). Despite clinical overlap, lack of true bradykinesia, presence of dystonia, and head tremor favored a diagnosis of SWEDDs, whereas re-emergent tremor, true fatiguing or decrement, good response to dopaminergic drugs, and presence of non-motor symptoms favored PD. A single tremor parameter could not differentiate between groups, but the combination of re-emergent tremor and highest tremor amplitude at rest was characteristic of PD tremor. SWEDDs and segmental dystonia patients exhibited an abnormal exaggerated response to the PAS protocol, in contrast to a subnormal response in PD and a normal response in ET. We conclude that despite clinical overlap, there are features that can help to distinguish between PD and SWEDDs which may be useful in clinical practice. The underlying pathophysiology of SWEDDs differs from PD but has similarities with primary dystonia. © 2010 Movement Disorder Society

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