Reading impairment in neurodegenerative diseases: a multiple single-case study

Abstract

ABSTRACTBackground: Reading impairment is frequently associated with neurodegenerative diseases, such as Alzheimer disease (AD), primary progressive aphasia (PPA), and posterior cortical atrophy (PCA). Notwithstanding the clinical relevance of reading processes in these conditions, only a relatively small number of studies have been published on this topic so far.Aims: We investigated the reading impairment in patients with different types of neurodegenerative diseases. In the light of the marked variability in pathological changes affecting brain areas potentially relevant to reading, it could be hypothesised that these neurodegenerative conditions may lead to different patterns of reading impairment.Methods & Procedures: Three groups of patients (AD, PPA, and PCA) and a control sample of neurologically healthy participants were examined with five tasks to test the ability to read and to repeat words and nonwords, as well as with an auditory and visual lexical decision task.Outcomes & Results: No specific pattern emerged as strongly diagnostic of a specific degenerative disease. Overall, AD and PPA patients were significantly more impaired in reading nonwords than words. Lexical decision impairment in the visual modality appears to be related to PCA, while a similar deficit in the auditory modality is more suggestive of AD. A multiple single-case analysis on the reading performance was run to identify the distribution of different kinds of dyslexia: phonological dyslexia occurred in 50% of patients affected by PCA: it occurred less often in patients affected by AD (15.8%) and PPA (16.7%). Surface dyslexia occurred only in one case of AD. Age of acquisition was predictive of the reading performance for AD patients, but not for PCA and PPA patients.Conclusions: Phonological dyslexia predominates in PCA. Surface dyslexia occurred only in one AD patient. Reading nonwords was predominantly impaired in AD and PPA cases. Impairment in visual lexical decision was associated with PCA, whereas a lexical decision deficit in the auditory modality emerged in AD. Data indicate the importance of extensive testing of reading and input lexical abilities in neurodegenerative diseases.