Abstract

Alzheimer's disease is characterized by progressive decline in several domains of cognitive functions, which have variable rates of change in the decline process. The overall objective of the study was to develop a model to predict the rate of decline in individual patients as measured by the Hierarchic Dementia Scale (HDS) based on the risk factors of age of symptom onset, education, gender, and place of residence. It was hypothesized that younger age of symptom onset would predict a faster rate of decline on the total HDS score and in the seven cognitive domains of orientation, language, memory, praxis, calculation, concentration, and perception. A related question concerned the contribution of specific cognitive functions of language and praxis in predicting rate of decline. This study examined 60 patients with Alzheimer's disease assessed at 6-month intervals over 18 months. At each assessment the HDS, an instrument, based on Piagetian concepts and neuropsychological findings, was administered to assess severity of impairment. Descriptive information were obtained at entry into the study. Using a repeated measures univariate and multivariate design format, the results show significant age and time effects for the total HDS score and for the seven cognitive domains. A model of decline in language and praxic functions was built using the Bayesian Information Selection Criterion (BIC). Of all the variables entered in the model (REML), age of onset, education level and place of residence were selected as predictors of decline. Regression analysis revealed that, for every year of difference in age of symptom onset there was a significant difference of 1.60 points on the total HDS score, .72 points on the language score and .26 points on the praxic score. The covariates of education and place of residence predicted significant decline on total HDS and language scores, but not on the praxic score. This study indicates that patients with Alzheimer's disease, who have earlier age of symptom onset, lesser education, and who live in an institution will decline faster on the total HDS and language function scores