Reading in neurodegenerative diseases: different impairments?

It is well known that neurodegenerative diseases may affect different areas of the brain, thereby giving rise to different patterns of cognitive deficits. We investigated reading performance in patients suffering from Alzheimer’s Disease (AD, n=19), Primary Progressive Aphasia (PPA, n=6: 4 logopenic, 1 semantic and 1 purely anomic aphasia) and Posterior Cortical Atrophy (PCA, n=4), plus a control group of healthy subjects (n=20). Participants were examined by means of tasks of auditory and visual lexical decision, word and non-word reading, reading trisyllabic words with unpredictable stress position (Toraldo et al, 2006) and word and non-word repetition. The lexical decision tasks proved relevant to differentiate AD and PCA patients, the former being disproportionately impaired in the auditory task while the opposite pattern emerged in the latter. Non-word reading was more impaired with respect to word reading in both AD and PPA patients. A multiple single case analysis of reading tasks identified phonological dyslexia in two out of four PCA participants (50%), much less so in AD (15.8%) and PPA (16.7%). Surface dyslexia occurred in one AD case only. We suggest that these results may be related to the different distribution of pathological changes in the three groups.