Handwriting Analysis in Parkinson's Disease: Current Status and Future Directions

Abstract

Background: The majority of patients with Parkinson's disease (PD) have handwriting abnormalities. Micrographia (abnormally small letter size) is the most commonly reported and easily detectable handwriting abnormality in patients with PD. However, micrographia is perhaps the tip of the iceberg representing the handwriting abnormalities in PD. Digitizing tablet technology, which has evolved over the last 2 decades, has made it possible to study the pressure and kinematic features of handwriting. This has resulted in a surge of studies investigating graphomotor impairment in patients with PD.

Methods: The objectives of this study were to review the evolution of the kinematic analysis of handwriting in PD and to provide an overview of handwriting abnormalities observed in PD along with future directions for research in this field. Articles for review were searched from the PubMed and SCOPUS databases.

Results: Digitizing tablet technologies have resulted in a shift of focus from the analysis of only letter size to the analysis of several kinematic features of handwriting. Studies based on the kinematic analysis of handwriting have revealed that patients with PD may have abnormalities in velocity, fluency, and acceleration in addition to micrographia. The recognition of abnormalities in several kinematic parameters of handwriting has given rise to the term PD dysgraphia. In addition, certain kinematic properties potentially may be helpful in distinguishing PD from other parkinsonian disorders.

Conclusion: The journey from micrographia to PD dysgraphia is indeed a paradigm shift. Further research is warranted to gain better insight into the graphomotor impairments in PD and their clinical implications.

Keywords: Parkinson's disease; dysgraphia; handwriting; micrographia.

Figure 1

A: Handwriting sample from an age‐matched, healthy control. B:) Handwriting sample from a patient during best on‐drug state showing visible improvement of horizontal micrographia. C:) Handwriting sample from a patient with Parkinson's disease during drug‐off state showing consistent, horizontal micrographia (from the authors’ unpublished collection).

Figure 2

A: Absolute velocity‐versus‐time graph from a healthy control. Local maxima and local minima are located. B: Absolute velocity‐versus‐time graph from a patient demonstrating primary and secondary submovements. In the graph, (O) indicates the start of the primary submovement, and (X) indicates the start of the secondary submovement (from the authors’ unpublished collection).

Figure 3

A: Absolute velocity‐versus‐time graph from a healthy control (corresponding to the handwriting sample in Fig. 1A) clearly shows fewer peaks and higher absolute velocity compared with patients who had Parkinson's disease (PD) during both drug‐off and drug‐on states. B: Absolute velocity‐versus‐time graph from a patient with PD during best drug‐on state (corresponding to the handwriting sample in Fig. 1B) shows a significant reduction in the number of peaks in velocity, suggesting a visible improvement in handwriting fluency. C: Absolute velocity‐versus‐time graph from a patient with PD during drug‐off state (corresponding to the handwriting sample in Fig. 1C) shows several peaks at various points, indicating a larger value of the number of inversions of velocity, hence suggesting dysfluent movement (from the authors’ unpublished collection).

Figure 4

Schematic presentation of a spectrum of handwriting abnormalities in patients with Parkinson's disease (PD). Note that certain parameters of handwriting, such as velocity and acceleration, are dependent on others, such as amplitude and size, respectively. Therefore, although the figure depicts the spectrum of handwriting abnormalities in PD, they may not be independent, as indicated in the figure. NIV indicates number of inversions of velocity; NIA, inversions of acceleration; RDP, ratio of deceleration phase.