Cognitive function in younger type II diabetes

To examine central nervous system involvement as a possible complication of diabetes by performing a comprehensive neuropsychological evaluation of relatively young (age < 55 years) NIDDM patients and a group of control subjects.

A cross-sectional comparative study of 28 patients, with duration of diabetes 5-18 years (mean +/- SD +/- 3.2 years), screened for acceptable glycemic control and absence of hypoglycemia on the day of examination, compared with 28 demographically similar, nondiabetic control subjects. Neuropsychometric tests performed were Mini-Mental Status Examination (MMSE), Neurobehavioral Cognitive Status Examination (NCSE), and P300 latencies (endogenous evoked potentials).

Seven (25.0%) patients reported history suggestive of cognitive impairment during day-to-day activities, and 17 (60.7%) had distal symmetrical polyneuropathy. Average P300 latencies were significantly delayed among the diabetic patients compared with the control subjects (349.5 +/- 28.2 vs. 312.9 +/- 19.3 ms; t = 5.68, P < 0.001). Although there was no significant difference in MMSE scores, compared with control subjects significantly more patients had impairment in NCSE tests of attention (chi 2 = 7.38, P < 0.01), repetition (chi 2 = 4.073, P < 0.05), and memory (chi 2 = 5.83, P < 0.05), while there was no significant difference in tests of comprehension, naming, construction, and calculation. Duration of diabetes, HbA1c levels, and the presence of distal symmetrical polyneuropathy among patients each did not correlate with any of the parameters of cognitive function evaluated. Higher blood glucose levels during the electrophysiological testing were associated with less delay in P300 latencies among the patients.

Central nervous system impairment, manifesting as mild impairments in certain cognitive skills, should be recognized as a possible complication of long-standing NIDDM, even in relatively younger individuals.