Clinical heterogeneity of probable Alzheimer's disease.

When the symptomatology in probable Alzheimer's disease (AD) was studied, two subgroups emerged: one with predominant cortical symptoms of parietal type (AD type I) and another with general cognitive symptoms but absence of or only mild cortical symptoms (AD type II). In AD type I, the age at onset was significantly lower, confusional symptoms and leukoariosis on computerized tomographic scan were less frequent, and the ganglioside GM1 concentration in cerebrospinal fluid was significantly higher than in AD type II. Although the significance of changes in cerebrospinal fluid gangliosides has not been fully elucidated, it is possible that the increase in cerebrospinal fluid GM1 reflects a more severe degeneration of neurons and synapses in AD type I than in AD type II. The relation between symptomatology and leukoariosis suggests that leukoariosis has clinical significance in AD patients. The total results suggest heterogeneity of probable AD. AD type I appears to constitute a classic AD subgroup with memory disturbances and marked cortical symptoms of parietal type, while age-related changes, vascular changes, and leukoariosis may be responsible for the more generalized symptomatology in AD type II.