To test the hypothesis that diabetes mellitus is associated with cognitive dysfunction, a battery of neuropsychological tests was administered to 75 diabetic adults and an equal number of demographically similar nondiabetic control subjects. Compared with control subjects, diabetic subjects performed significantly more poorly on measures of psychomotor efficiency and spatial information processing. In contrast, no between-group differences appeared on measures of verbal intelligence, learning, memory, problem solving, or simple motor speed. Results from multiple regression analyses showed that clinically significant distal symmetrical polyneuropathy was strongly associated with psychomotor slowing, whereas, glycosylated hemoglobin values were weakly associated with both psychomotor slowing and spatial processing. No other biomedical variables predicted cognitive test performance. These neurobehavioral data are consistent with the hypothesis that a “central neuropathy” may be associated, at least in part, with chronic hyperglycemia.

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