Characteristics of handwriting of patients with Huntington's disease

Patients with Huntington's disease exhibit poorer-quality handwriting, sometimes clinically exhibiting macrographia, an increase in the size of handwriting. To characterize deficits in handwriting of patients with Huntington's disease, we compared the writing of 12 young, 12 age-matched controls, and 12 patients with Huntington's disease. Subjects were asked to write the letter "l" four times, at a constant length, on a graphics tablet that sampled pen position at 200 Hz. Huntington's disease causes chorea (involuntary movement), akinesia (difficulty in initiating voluntary movement), and bradykinesia (slowness and difficulty in maintaining voluntary movement). To distinguish changes in handwriting quality due to involuntary movement from impairments of voluntary movement, handwriting samples with obvious choreic movements were analyzed separately from other handwriting samples. Several measures of quality of handwriting were considered, based on: the regularity and consistency of handwriting, the efficiency of movement trajectories, and the proportions of movement occurring at specific frequencies. Results suggested that Huntington's disease increases variability of movement parameters, and causes problems in producing smooth movements. Choreic movement was best characterized by the number of zero crossings in the velocity function relative to the prescribed number of writing strokes. We hypothesize that macrographia in Huntington's disease occurs when chorea predominates over bradykinesia. Comparisons were made between the handwriting of patients with Huntington's and Parkinson's diseases.