[1] UCL Inst Neurol, Sobell Dept Motor Neurosci & Movement Disorders, London WC1N 3BG, England
[2] Univ Med Ctr Hamburg Eppendorf UKE, Dept Neurol, D-20246 Hamburg, Germany
[3] Kings Coll Hosp NHS Fdn Trust, Dept Neurol, London SE5 9RS, England
[4] Lewisham & Greenwich NHS Trust, Queen Elizabeth Hosp, Dept Neurol, London SE18 4QH, England