Multiple patterns of writing disorders in dementia of the Alzheimer's type and their evolution

This paper reports the results obtained from a writing task given to 23 Italian patients suffering from mild to moderate dementia of the Alzheimer's type (DAT). Spelling performance was tested with a task that taps the sub-word-level (spelling of regular words and nonwords), and the lexical route (spelling of regular and irregular words), in line with contemporary models of writing. Each patient's performance was classified according to the emergence of dissociated patterns of damage between regular words and nonwords and between regular and irregular words. The 23 DAT patients span the whole spectrum of dysgraphic taxonomy; five showed the characteristic pattern of impairment of surface dysgraphia, two showed the characteristics of phonological dysgraphia, while a mixed pattern (i.e. better performance on regular words compared to irregular words and regular nonwords) emerged in seven cases. Three patients presented undifferentiated writing disorders, two were completely agraphic, while four patients showed only minimal or no writing defects. The rate of dissociated impairments in the lexical and the sub-word-level routine is very similar to that observed after acute focal brain damage, which contradicts the hypothesis that degenerative brain damage selectively impairs writing performance along the lexical-semantic route. To test the hypothesis that surface sub-word-level processing abilities are affected only during the evolution of the disease, nine patients were tested longitudinally after an interval of 6-12 months. Once again, the data showed high variability across subjects, and do not seem to support involvement of the sub-word-level spelling routine only at a late stage in the development of the disease.