Kinematic Analysis of Handwriting in Focal Hand Dystonia

My project is part of a larger study entitled Therapeutic Effects of Transcranial Electrical Polarization (TEP) in Patients with Focal Hand Dystonia (FHD). This study looks at the effects of TEP on FHD patients through changes in handwriting. Dystonia is a neurological disorder characterized by excessive movements, which lead to sustained involuntary movements, distorted voluntary movements and abnormal posture. Idiopathic adult onset focal hand dystonias are often task specific and include writer's cramp, musician's cramp and golfer's cramp. This study focused on the treatment of writer's cramp. My project was to formulate a new method of quantifying handwriting, our primary outcome measure. The study used a digital writing tablet along with handwriting analysis software to record the subject's handwriting. The writing sample was analyzed using software which calculates a large number of variables. According to the protocol selected variables were to be plugged into an equation in order to create a composite score. After researching previous studies and performing preliminary data analysis we found a number of flaws in the proposed composite score. The first major issue was that the composite score considered the average pen force during writing. The tablet only measures up to 5N of force which was inadequate since the writer's cramp patients often write with more then 5N of force. Additionally the tablet only measures the force perpendicular to the plane of the tablet and not parallel to the tablet which invalidates the actual force measurement. The second problem with the composite score was that it considers the mean letter stroke length. When we isolated this variable in writer's cramp patients and compared it to healthy patients we found there was no difference between the two groups. We therefore decided that a improved method of computing changes in handwriting was needed. A number of studies have proposed different methods of improving writer's cramp but there is no consensus in terms of quantifying the progress of the treatment. In order to determine the best method of computing handwriting changes we analyzed handwriting samples from healthy and writer's cramp patients. In total handwriting samples from ten healthy and ten dystonic patients were recorded. In order to increase accuracy each subjects performed five different writing tasks. Of the thirteen variables analyzed six variables showed significant differences between healthy and dystonic patients in all five of the handwriting tasks performed. The variables which were found to be the most significant were the number of inversions in the velocity (NIV) and acceleration (NIA) profile (a measure of handwriting smoothness), the standard deviation of the NIV, the frequency of strokes, velocity of the pen on paper, and the mean positive stroke duration (a measure of speed).

In light of our findings we decided to abandon the composite score originally proposed and instead analyze changes in our six individual variables over the course of treatment.