Cognitive function in diabetes mellitus: the effects of duration of illness and glycaemic control.

Post-mortem studies suggest that chronic, poorly controlled diabetes mellitus might be associated with degenerative changes in the central nervous system. However, the evidence that these changes are reflected in any impairment of cognitive performance is equivocal. The study reported here evaluated the effects of duration of illness and glycaemic control upon memory function in 40 cases of insulin-dependent diabetes mellitus (IDDM). Duration of illness was inversely related to performance, but degree of glycaemic control had no effect at all. This suggests that any impairment of cognitive function associated with IDDM is more likely to be attributable to the impact of suffering from a life-threatening disease rather than to organic neurological damage. The effect of chronicity was somewhat more pronounced in the case of concrete material than in the case of abstract material, and it is suggested that chronic IDDM might be associated with a specific impairment in elaborative encoding.