Patterns of Cognitive Impairment in Neurological Disease

Cognitive impairment is present in neurodegenerative disease, usually as part of a spectrum of symptoms that includes different domains of cognitive function. While the nature of the cognitive impairment tends to be diseasespecific, the aspects of cognitive impairment seen in different disease entities overlap considerably. This overlap makes distinctions among them difficult and, when considered with accumulating insights from molecular genetic and neuropathological analyses, increasingly suggests that different neurodegenerative diseases share not only aspects of their symptomatology but also their pathogenesis. This realization has prompted a reconsideration of the classification of these diseases. Reexamination of the clinical phenotypes of different neurodegenerative diseases has revealed that cognitive impairment is more commonly present than previously thought. Thus, the comparison of the patterns of cognitive impairment in different neurodegenerative diseases, when combined with molecular genetic, neuropathological, and imaging analyses, has considerable heuristic value. This review focuses on cognitive impairment in Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), which can be considered “pure neurodegenerative diseases”, and in multiple sclerosis (MS), whose pathogenesis includes both neurodegenerative and autoimmune processes. Rather than presenting an exhaustive description of studies addressing cognitive impairment in these diseases, it attempts to highlight the emerging patterns of cognitive impairment associated with the temporal and spatial context of their neurodegenerative processes.