Brain Advance Access published online on January 29, 2009
Brain, doi:10.1093/brain/awn363
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Case-control study of writer's cramp
1 Department of Neurology, Hôpital Pitié-Salpêtrière, Paris F-75013, France 2 CNRS, UMR 7102, Paris F-75005, France 3 UPMC Univ Paris 6, Paris F-75005, France 4 Inserm, U708, Paris F-75013, France 5 Clinical Investigation Center, Saint-Antoine University Hospital, Paris F-75012, France 6 National Center for MSA, Sleep Department and Department of Neurology, Purpan Hospital, Toulouse, France 7 Department of Neurology, Stroke Unit, Centre R. Garcin, Hôpital Sainte Anne, Paris F-75014, France 8 Inserm, U894, Paris F-75005, France 9 Inserm, U679, Paris F-75013, France
Correspondence to:
Dr E. Roze, Pôle des Maladies du Système Nerveux, Service de Neurologie, Hôpital de la Salpêtrière, 47-83 Bd de l’Hôpital, 75651 Paris Cedex 13, France E-mail: emmanuel.roze{at}psl.aphp.fr
Task-specific focal dystonias are thought to be due to a combination of individual vulnerability and environmental factors. There are no case-control studies of risk factors for writer's cramp. We undertook a case-control study of 104 consecutive patients and matched controls to identify risk factors for the condition. We collected detailed data on medical history and writing history as part of hobbies or occupation. Cases had a college or university degree more frequently than controls [OR = 4.6 (1.3–20.5), P = 0.01]. The risk of writer's cramp increased with the time spent writing each day (P-trend = 0.001) and was also associated with an abrupt increase in the writing time during the year before onset (OR = 5.7, 95% CI = 1.3–33.9, P = 0.02). Head trauma with loss of consciousness [OR = 3.5 (1.0–15.7), P = 0.05] and myopia [OR = 4.1 (1.7–12.0), P = 0.0009] were both associated with the condition but it was not significantly associated with peripheral trauma, left-handedness, constrained writing, writing in stressful situations or the choice of writing tool. The dose–effect relationship between writer's cramp and the time spent handwriting each day, and the additional burden of acute triggers such as an abrupt increase in the writing time in the year before onset, point to a disruptive phenomenon in predisposed subjects. Homeostatic regulation of cortical plasticity may be overwhelmed, resulting in dystonia.
Key Words: dystonia; case-control; risk factors; cortical plasticity; head trauma
Received June 10, 2008. Revised November 27, 2008. Accepted December 10, 2008.