Impairment of written word production in logopenic primary progressive aphasia: dissociating phonological and orthographic contributions

Introduction: Written language impairment is a frequent but still incompletely understood feature of the logopenic variant of primary progressive aphasia (lvPPA), and although spoken language deficits have been extensively studied, less is known about the mechanisms underlying impaired written word production and the conditions under which orthographic representations become particularly vulnerable. In this study, we investigated written language processing in individuals with lvPPA using a battery of tasks designed to dissociate phonological and orthographic contributions. Methods: Twelve participants with lvPPA and thirteen healthy controls completed written picture naming, written word dictation, written non-word dictation, grapheme dictation, and a picture-based letter-in-word judgment task that probed orthographic knowledge without requiring overt written output. Results: Compared with controls, participants with lvPPA showed significant impairments in written picture naming, written word dictation, grapheme dictation, and letter-in-word judgment, whereas written non-word dictation was relatively preserved at the group level. Within grapheme dictation, vowel graphemes were disproportionately affected relative to consonants. In the letter-in-word judgment task, the largest group differences were observed in conditions requiring access to orthographic knowledge when phonological cues were non-informative. Discussion: Together, these findings indicate that written language impairment in lvPPA cannot be explained by a primary phonological deficit alone but instead reflects vulnerability of abstract orthographic representations, particularly under conditions of increased orthographic ambiguity. Identifying tasks that require access to orthographic knowledge independently of phonological support may therefore provide sensitive markers for characterizing written language impairment in lvPPA and contribute to a more precise understanding of language network dysfunction in neurodegenerative disease.