Dysgraphia Phenotypes in Native Chinese Speakers With Primary Progressive Aphasia

Abstract

Background and objectives: Most primary progressive aphasia (PPA) literature is based on English language users. Linguistic features that vary from English, such as logographic writing systems, are underinvestigated. The current study characterized the dysgraphia phenotypes of patients with PPA who write in Chinese and investigated their diagnostic utility in classifying PPA variants.

Methods: This study recruited 40 participants with PPA and 20 cognitively normal participants from San Francisco, Hong Kong, and Taiwan. We measured dictation accuracy using the Chinese Language Assessment for PPA (CLAP) 60-character orthographic dictation test and examined the occurrence of various writing errors across the study groups. We also performed voxel-based morphometry analysis to identify the gray matter regions correlated with dictation accuracy and prevalence of writing errors.

Results: All PPA groups produced significantly less accurate writing responses than the control group and no significant differences in dictation accuracy were noted among the PPA variants. With a cut score of 36 out of 60 in the CLAP orthographic dictation task, the test achieved sensitivity and specificity of 90% and 95% in identifying Chinese participants with PPA vs controls. In addition to a character frequency effect, dictation accuracy was affected by homophone density and the number of strokes in semantic variant PPA and logopenic variant PPA groups. Dictation accuracy was correlated with volumetric changes over left ventral temporal cortices, regions known to be critical for orthographic long-term memory. Individuals with semantic variant PPA frequently presented with phonologically plausible errors at lexical level, patients with logopenic variant PPA showed higher preponderance towards visual and stroke errors, and patients with nonfluent/agrammatic variant PPA commonly exhibited compound word and radical errors. The prevalence of phonologically plausible, visual, and compound word errors was negatively correlated with cortical volume over the bilateral temporal regions, left temporo-occipital area, and bilateral orbitofrontal gyri, respectively.

Discussion: The findings demonstrate the potential role of the orthographic dictation task as a screening tool and PPA classification indicator in Chinese language users. Each PPA variant had specific Chinese dysgraphia phenotypes that vary from those previously reported in English-speaking patients with PPA, highlighting the importance of language diversity in PPA.

Figure 1. Definition and Examples of the Writing Errors Found in the Study Participants (n = 53)

The alphabets written within // represent the Pinyin pronunciation (the official romanization system of Chinese language) of the Chinese characters (e.g., /xie/) and the numerals within the // denote the lexical tones of the Chinese character (e.g., /2/); English translations of the Chinese characters are provided in square brackets.

Figure 2. Orthographic Dictation Performance in Chinese Cognitively Normal Individuals and Patients With PPA

(A) Orthographic dictation accuracy (mean and SD) across cognitively normal (n = 20) and primary progressive aphasia (PPA) groups (semantic variant PPA [svPPA], n = 10; nonfluent/agrammatic variant PPA [nfvPPA], n = 9; logopenic variant PPA [lvPPA], n = 21). (B) Receiver operating characteristic (ROC) curve of the orthographic dictation task in identifying PPA cases (n = 40) from the cognitively normal participants (n = 20). Using 36 out of 60 as the cutoff value, the sensitivity and specificity of the test reached 90% and 95%, respectively, with area under the curve value of 0.941 (p < 0.0001). (C) The vector projections of 8 dysgraphia types from principal component analysis with 3 factors derived. The dysgraphia types in factors 1, 2, and 3 are represented in red, green, and blue circles and fonts, respectively. (D) The prevalence of factors 1, 2, and 3 across cognitively normal (n = 20) and PPA groups (svPPA, n = 10; nfvPPA, n = 9; lvPPA, n = 21) presented in box plot format.

Figure 3. Neuroanatomical Correlations of Orthographic Dictation Accuracy and Dysgraphia Types

Neuroanatomical correlation analysis of orthographic dictation accuracy and the prevalence of dysgraphia types with the gray matter volumetric changes. We adopted the voxel-based morphometry method with multiple linear regression models adjusted for age at examination, education, total gray matter volume, diagnosis, or dictation accuracy. The cluster threshold was corrected for family-wise error with p value set at <0.05 and the voxel was set at a threshold of k > 80. No suprathreshold clusters were noted for perseveration, motor, stroke, or radical writing errors.

Figure 4. Cognitive Architectural Model of Orthographic Dictation in Chinese Language Users

This is a schematic cognitive architecture model of orthographic dictation for Chinese language users with additional homophone and orthographic selection processes included. For a pictographic character such as “弓” (/gong1/bow), there are 8 other common homophones “公、工、宮、功、攻、恭、躬、蚣.” As the auditory stimuli specified that target character to be “弓箭的弓” (the character “bow” in the word “bow and arrow”), Chinese language users are thus able to select the target character. This process is critical for the homophone-rich Chinese language and reliant on semantic knowledge and lexical retrieval functions, which are impaired in semantic variant primary progressive aphasia (svPPA) and logopenic variant primary progressive aphasia (lvPPA). Chinese language is also rich in compound words, with most of its characters constructed by assorted radicals. In individuals with nonfluent/agrammatic variant primary progressive aphasia (nfvPPA), the orthographic long-term memory impairment coupled with the inability to suppress the other frequently paired characters or to select the accurate radicals would result in compound word (e.g., for “霓虹的”/“霓”) or radical (e.g., for “趣”) writing errors. The visuospatial complexity of Chinese characters requires a higher demand for orthographic working memory and motor functions. When impaired, Chinese language users produce orthographically similar writing errors (e.g., for “龜”) or motor dysgraphia (e.g., for “電”), as noted in participants with lvPPA and participants with nfvPPA. Contrary to English language users, sublexical phonology–orthography conversion such as surface dysgraphia (e.g., for “殯”) is uncommon.