A Kinematic Study of Progressive Micrographia in Parkinson's Disease

Abstract

Progressive micrographia is decrement in character size during writing and is commonly associated with Parkinson's disease (PD). This study has investigated the kinematic features of progressive micrographia during a repetitive writing task. Twenty-four PD patients with duration since diagnosis of <10 years and 24 age-matched controls wrote the letter “ e ” repeatedly. PD patients were studied in defined off states, with scoring of motor function on the Unified Parkinson's Disease Rating Scale Part III. A digital tablet captured x-y coordinates and ink-pen pressure. Customized software recorded the data and offline analysis derived the kinematic features of pen-tip movement. The average size of the first and the last five letters were compared, with progressive micrographia defined as >10% decrement in letter stroke length. The relationships between dimensional and kinematic features for the control subjects and for PD patients with and without progressive micrographia were studied. Differences between the initial and last letter repetitions within each group were assessed by Wilcoxon signed-rank test, and the Kruskal-Wallis test was applied to compare the three groups. There are five main conclusions from our findings: (i) 66% of PD patients who participated in this study exhibited progressive micrographia; (ii) handwriting kinematic features for all PD patients was significantly lower than controls ( p < 0.05); (iii) patients with progressive micrographia lose the normal augmentation of writing speed and acceleration in the x axis with left-to-right writing and show decrement of pen-tip pressure ( p = 0.034); (iv) kinematic and pen-tip pressure profiles suggest that progressive micrographia in PD reflects poorly sustained net force; and (v) although progressive micrographia resembles the sequence effect of general bradykinesia, we did not find a significant correlation with overall motor disability, nor with the aggregate UPDRS-III bradykinesia scores for the dominant arm.

Neural substrates underlying progressive micrographia in Parkinson's disease

“…We decided to use our own criteria for PM because we could not detect PM in the free writing by using Kim et al's criteria, even though there were PD patients with PM whose B value (by Kim et al's definition) was greater than the mean −2 SD of that of the HCs (Figure 1; Kim et al., 2005). The prevalence of PM in free writing in the current study was naturally higher than that in Kim et al's study, almost the same as that in McLennan et al's study, but lower than those in Shukla et al's (51.5%) and Zham et al's (66%) studies (Kim et al., 2005; McLennan et al., 1972; Wagle Shukla et al, 2012; Zham et al, 2019). In Shukla et al's and Zham et al's studies, the authors used the English letters, and the subjects were required to write a single letter twenty times on a paper.…”

“…We decided to use our own criteria for PM because we could not detect PM in the free writing by using Kim et al's criteria, even though there were PD patients with PM whose B value (by Kim et al's definition) was greater than the mean −2 SD of that of the HCs (Figure 1; Kim et al, 2005). The prevalence of PM in free writing in the current study was naturally higher than that (Kim et al, 2005;McLennan et al, 1972;Wagle Shukla et al, 2012;Zham et al, 2019 In the current study, the prevalence of PM in the free writing task was 10% in the HC group, and there was no significant difference in the Corrected B values or the prevalence of PM in the free writing task between the PD and HC groups. In addition, if we did not set the cutoff value of the corrected B value at the mean −1.5 SD of that of the HCs, the prevalence of PM in the free writing task would have been 25% in the PD group and 20% in the HC group.…”

“…To the best of our knowledge, no studies have systemically investigated the prevalence of CM or PM in elderly people. Moreover, previous studies in PD patients with micrographia did not report the prevalence in healthy controls except for Zham et al's study (Kim et al., 2005; McLennan et al., 1972; Wagle Shukla et al, 2012; Zham et al, 2019). In Zham et al's study, the prevalence of PM was 16.7% in free writing.…”

Differences in Levodopa Response for Progressive and Non-Progressive Micrographia in Parkinson's Disease

“…Independent sample t-test was performed to compare PD and control groups to confirm age-matching, while Chi-Square test was performed for differences in gender and handedness (10).…”

“…The establishment of a ‘typical' historical script size is one limitation, since writing size varies considerably in a normal subject depending on writing context ( 9 ). In a previous study, we found that classifications of consistent micrographia based on letter size did not yield a distinct subset ( 10 ). Only 4% had a purely consistent pattern, while some PD patients with decrement also fell below the consistent cut-off.…”