Event related potential P300 as a measure of auditory evoked potential In type 2 diabetic patients: correlation with micro vascular complications and the different parameters of metabolic control particularly previous hypoglycemic episodes

ABSTRACT

Impaired cognitive functions are one of the major CNS complications of diabetes. Chronic hyperglycemia, chronic hyperinsulinaemia, chronic hypertension, dyslipidaemia, cardiovascular diseases and drugs, are among the contributing factors for the occurrence of CNS complications of diabetes. Tight metabolic control definitely reduces the risk of diabetic complications but is associated with increased risk of hypoglycaemia. Severe hypoglycaemia by itself can cause severe and irreversible brain damage, however, the impact of hypoglycaemia on CNS complications is not definite. Event-related potential [ERP] P300 auditory evoked potential measure reflects the speed of neural events related to attention and short term memory; both are important and essential cognitive functions. Increased ERP P300 latency has been associated with early abnormalities in psychometric tests in diabetic patients. We studied the ERP P300 latency -as an indirect index of cognitive functions- and its relation to the different microvascular complications and the different parameters of control of Type 2 diabetes to try to find predictive factors for early intervention in such patients before sever cognitive impairment occurs. Also, we tried to correlate it with the number and severity of hypoglycaemic episodes to evaluate the effect of hypoglycaemia on cognitive functions. The study was carried out on 50 type 2 diabetic patients with no clinical evidence of cerebral dysfunctions or cognitive impairment and 20 controls. All the patients and controls were subjected to full clinical examination including neurological examination. Those with abnormality suggestive of peripheral neuritis were subjected to sural nerve sensory conduction velocity [SNSCV]. Blood samples were taken to measure fasting blood glucose and HbA 1c. Urine was tested by micral test for immunochemical semi quantitative determination of microalbuminurea. Diabetic retinopathy was detected by ophthalmologic examination after dilatation of the pupil Cognitive functions were examined and a Minimental State Examination [MMSE]. Questions were put in clear Arabic language. Hypoglycaemia was evaluated through history interrogation. ERPs were obtained by the conventional technique with an acoustic ball paradigm. Diabetic subjects had significantly higher incidence of retinopathy, neuropathy, microalbuminurea, fasting blood glucose level and Hb A[1c] than the control subjects. Diabetic patients had higher ERP P300 than the control subjects. ERP 300 was correlated to age and the presence of both peripheral neuritis and microalbuminurea, and not to the duration of diabetes, glucose levels, HbA1c, TG, cholesterol or the presence of retinopathy. There was no difference in ERP 300 latency when we compared the diabetic patients according to the number or severity of previous hypoglycaemic episodes. Patients with no history of previous hypoglycaemic episodes showed a tendency towards a lower ERP 300 latency but this was not statistically significant. There was a collinear relationship between the prolongation of ERP P300 and both the age of the patients and the degree of shortening of the SNSCV. There was no collinear relationship between ERP P300 and the degree of microalbuminurea [quantitatively]. ERP P300 is an easy test to apply in diabetic patients as a test of early changes in brain functions. It is not influenced by the number or severity of previous Hypoglycaemic attacks. Previous attacks of hypoglycemia although of a potential lethal effects could be less dangerous in type 2 diabetic patients than was previously expected and the brain functions of type 2 diabetes patients may be less vulnerable to the effect of hypoglycaemia. Aging, the presence of microalbuminurea and the degree of peripheral neuritis are associated with deterioration of ERP P300. There is a linear relationship between age and the degree of peripheral neuritis on one hand and the deterioration of ERP P300 on the other hand