Impaired phonological reading in primary degenerative dementia

This case study reports the profile of preserved and impaired capacities in a left-handed patient suffering from primary degenerative dementia of unknown aetiology. She was remarkable because her relatively preserved object naming and semantic categorization abilities contrasted with severe deficits in speech fluency, oral reading, inability to execute spoken and written commands, and severely impaired auditory-verbal short-term memory. Her reading disorder could be characterized as a disturbance of assembled phonology. She had great difficulty reading pronounceable nonwords, but she could correctly read irregular words. She showed effects of word imageability or concreteness (more than word frequency). She also showed effects of part-of-speech, where nouns and adjectives were read more easily than inflected verbs. She had difficulty reading function words. The syntactic category effects could be proven (by hierarchical log-linear analysis) not to be an artefact of imageability differences between verbs, adjectives and nouns. In reading aloud she made visual and morphological errors, but no semantic errors. This interesting pattern of preserved semantic information and disrupted phonological processing is unusual in dementia and contrasts with the severe dysnomia of patients with surface dyslexia who are able to read by the indirect, assembly-of-phonology route and show better reading of nonwords than irregular words. Her reading by a direct visual-semantic route appeared to be associated with relatively intact object naming, concrete word reading, and irregular word reading. This selective impairment of phonological reading in the context of partly preserved semantic abilities was interpreted as confirmation of the dissociability of language functions in primary degenerative dementia.