Symptom Progression in Alzheimer's Disease

To the Editor:—To date there is no satisfactory explanation for the large inter-individual variation in symptom progression in Alzheimer's disease (AD). Rapid symptom progression, however, has been reported to correlate with early age of onset.1, 2 We therefore examined the hypothesis that the annual rate of symptom progression in AD is related to onset age with two approaches. Study 1: In a cross-sectional study of 152 patients with AD according to ICD-10 research criteria, the following definition of annual symptom progression was used: The difference between the present Mini-Mental State score,3 which is a global measure of cognitive impairment, and the estimated pre-morbid score on this scale of 284 was divided by the number of years since symptom onset. The individual rate of annual symptom progression was correlated with onset age. Pearson correlation coefficient was r = 0.12. Study 2: In a longitudinal study 56 patients with AD according to the ICD-10 research criteria at baseline were investigated again after 12 months, using two clinical measures for annual symptom progression: Mini-Mental State Examination (MMSE) and Cambridge Cognitive Examination,5 a cognitive test battery which covers a wider range of cognitive functions than the MMSE. The difference between the two test scores of each measure, reflecting the individual rate of annual symptom progression, was correlated with onset age. Coefficients of correlation were r = 0.17 (MMSE) and r = 0.03 (CAMCOG). In both studies (1 and 2) the hypothesis that symptom progression in AD is related to onset age could not be confirmed. Thus, cross-sectional and longitudinal data suggest that symptom progression in Alzheimer's disease is not related to onset age. These results are in accordance with the findings of Dastoor and Cole6 and Ortof and Crystal.7 The predominance of a rapid symptom progression among early onset cases, as described by Albert,1 may be due to the high prevalence of additional physical diseases in her presenile group.