Language impairment in dementia of the Alzheimer type: a hierarchical decline?

Progressive memory impairment is the primary cognitive feature of Alzheimer's disease. Systematic attention to progressive language impairment is under-appreciated. The purpose of this article is to apply the semiotic language framework to organize the disparate findings on language impairment in DAT.

The semiotic system is hierarchical, going from simple to more complex units of language, with the hierarchical ranks of phonology, morphology, syntax, semantics. This language hierarchy is used as an organizing tool to provide a context for the discrete data on language decline in DAT. Studies relating to language impairment in DAT were identified through an exhaustive computerized search (Medline and Psych Info Database) of available literature spanning the last forty years in which 615 references were examined. Papers were selected for review if reference were made to any one or more of the language parameters of phonology, morphology, syntax, semantics, or to any components or indicators of these parameters, such as sound production, naming, grammar, sentence processing, verbal comprehension in Alzheimer patients.

There appears to be an overall relation between language decline and complexity of language both across and within the hierarchical ranks. There also appears to be an associated negative relation between sequence in language development and language decline. Language forms learned last in the sequence of language development are the most complex and appear to be first to deteriorate.

The decline of language in DAT appears to be hierarchical in nature. Further understanding of this hierarchical language decline depends in part on nosologic clarification and subtyping of DAT.