Circumscribed cognitive dysfunction in middle-aged adults with type 2 diabetes.

OBJECTIVE: To examine the extent to which type 2 diabetes is associated with poorer performance on measures of learning, memory, psychomotor speed, and problem-solving in middle-aged adults. RESEARCH DESIGN AND METHODS: This cross-sectional study evaluated 50 adults (age range 34-65 years, mean 50.8) with type 2 diabetes and 50 demographically similar community control subjects without diabetes. Each subject received a thorough physical examination and a detailed neuropsychological assessment. Factor analysis was used to assign specific tests to 1 of 4 cognitive domains (learning, memory for stories, problem-solving, and psychomotor speed). Hierarchical regression analysis was used to identify demographic and biomedical variables associated with cognitive dysfunction. RESULTS: Learning, memory, and problem-solving skills were unaffected by type 2 diabetes. In contrast, psychomotor slowing was predicted by a diagnosis of diabetes (r2 change = 0.075, P < 0.002) with additional variance in psychomotor efficiency explained independently by HbA1 (r2 = 0.064, P < 0.003) and vibratory threshold (r2 = 0.112, P < 0.0001). The magnitude of psychomotor slowing on specific tests ranged from 12% (Digit Vigilance) to 23% (Grooved Pegboard). CONCLUSIONS: Middle-aged adults with type 2 diabetes manifest psychomotor slowing that is associated with poorer metabolic control, whereas learning, memory, and problem-solving skills appear to be largely intact. The development of psychomotor slowing may be a manifestation of a "central neuropathy" induced by chronic hyperglycemia.