Central and peripheral agraphia in Alzheimer's disease: from the case of Auguste D. to a cognitive neuropsychology approach.

Since the observation of Auguste D. by Alöis Alzheimer, it is an acknowledged fact that writing is one of the cognitive functions that are weakened early in Alzheimer's disease (AD). This study aimed to examine the cognitive nature of this disorder and question the hypothesis of a standard progression (Platel et al., 1993) from lexical to other central and more peripheral processes. A large group of mild to moderate AD patients (n=59) and a group of healthy elderly controls were submitted to an extensive assessment of both the central and peripheral components of writing. A comparison of groups indicated that AD patients performed more poorly than controls on a wide range of writing measures. It revealed a predominantly lexical disorder, but also found evidence of associated disorders located at different stages in the spelling system (phonological route, graphemic buffer, allographic store, graphic motor patterns). A multiple single-case analysis, using a specific methodology, allowed us to delimit individual profiles of agraphia. It revealed a wide variety of agraphia syndromes, including a far from negligible number of patients with selective damage to one of the central or peripheral components, as well as patients with multiple writing impairments. A positive correlation was observed between the severity of the dementia and spelling/writing measures (lexical and allographic). This study does not support the hypothesis of a uniform progression. Rather, it points to heterogeneous profiles of agraphia and suggests that the first signs of writing impairment in AD stem from changes at different points in the broad anatomical network subserving spelling and writing abilities.