Language disintegration in dementia: effects of etiology and severity

The speech characteristics on a standardized picture description task of 26 subjects with presumed senile dementia of the Alzheimer type (SDAT) and 13 subjects with stroke-related dementia (SRD) were compared to 15 normal subjects over age 59 years. Compared to the normal subjects, the dementia subjects used fewer total words, fewer unique words, fewer prepositional phrases, fewer subordinate clauses, and more incomplete sentence fragments. Lexical deficits tended to be more severe than syntactic ones, confirming prior suggestions that lexicon is more vulnerable to disruption in dementia than syntax. Greater dementia severity among the SDAT subjects was associated with marked difficulties in accessing the mental lexicon (increased use of empty words, indefinite anaphora, and pronouns). Greater dementia severity in the SRD subjects was associated with laconic speech that was syntactially less complex. Diffuse brain injury (as typified by SDAT) appears to disproportionately affect lexicon whereas multifocal injury (as typified by SRD) has a disproportionate effect on syntax (assuming that focal lesions of the posterior language zone have been excluded). The speech characteristics of the mild SDAT subjects showed similarities to those of anomic or semantic aphasia whereas the speech of the more advanced SDAT subjects showed similarities to Wernicke aphasia or transcortical sensory aphasia. The speech of the subjects with more severe SRD showed some similarities to Broca aphasia. The most important nonlinguistic deficit in both the SRD and the SDAT groups was a failure to make relevant observations during the picture description task. Perseverations were present in the speech of both the SRD and SDAT subjects, whereas aposiopesis, logorrhea, and palilalia were more typical of the SDAT subjects. Laconic speech was more characteristic of the SRD subjects.