Multiple types of dyslexia in primary progressive aphasia

Background Primary progressive aphasia (PPA) is a neurocognitive syndrome hallmarked by decline in language-related cognitive abilities. Although reading is an essential cognitive ability for communication and everyday activities, reading impairment, dyslexia, is under-researched in PPA compared to speech production and comprehension. Dyslexia research in PPA focuses on only two types: surface and phonological dyslexia, even though many more types are known to occur in non-neurodegenerative brain disease.Aims To investigate the frequency and types of dyslexia in a case series of patients with PPA.Methods Forty PPA participants completed a comprehensive reading assessment examining reading lists of words, nonwords, and word-pairs that are sensitive to the identification of at least 13 dyslexia types. Types of reading errors were analyzed to determine the dyslexia type for each participant with dyslexia. The participants also underwent comprehensive language and neurocognitive assessment.Results Dyslexia was identified in 83% of the PPA participants, manifesting in 11 distinct dyslexia types: surface, attentional, phonological output buffer, orthographic input buffer, phonological conversion, vowel, letter-position, visual, voicing, morphological-conversion, and deep dyslexias. Five of these types of dyslexia have not been previously reported in PPA or other dementias. We found a double dissociation between surface dyslexia and semantic impairment and dissociations between phonological dyslexia and a phonological impairment in production.Conclusions The results underscore the need for refined assessment tools for diagnosing dyslexia in PPA, based on a theory of reading, that is able to identify the various dyslexia types. Accurate identification of identifies dyslexia types can guide targeted individualized interventions.