The majority of diabetic patients have multiple risk factors for vascular disease, however diabetes remains an independent risk factor for stroke across all age groups (Wolf etal., 1983). This increased risk is not confined to patients with diabetes but also includes patients with impaired glucose tolerance (IGT), asymptomatic non-fasting hyperglycaemia and hyperinsulinaemia (Coutinho etal., 1999). The increase in risk conferred by diabetes also extends to patients with hypertension who already have a high absolute risk of cardiovascular disease (Kannel and McGee, 1979; Stamler etal., 1993).
It has long been recognised that usual blood pressure levels are directly and continuously associated with risk of stroke in patients with or without a previous history of hypertension (Prospective Studies Collaboration, 1995; Eastern Stroke and Coronary Heart Disease Collaborative Research Group, 1998). A meta-analysis of studies examining the relationship between fasting, postprandial and casual glucose levels has demonstrated a similar relationship between glucose levels and cardiovascular risk. Furthermore, like blood pressure, this increased risk extends below diabetic and IGT thresholds and into the 'normal' range (Coutinho etal., 1999).
Accepting that type 2 diabetes is the predominant form of diabetes in stroke patients, the United Kingdom Prospective Diabetes Study (UKPDS) has demonstrated that over a 9-year period 20% of type 2 diabetic patients are likely to experience macrovascular complications (UK Prospective Diabetes Study Group, 1996). This is in contrast to an estimated 9% experiencing microvascular complications over a similar period. Overall, macrovascular complications account for 50% of deaths in such patients (Reichard etal., 1991; Ohkubo etal., 1995; UK Prospective Diabetes Study Group, 1996). Diabetes confers an increased risk of stroke through a number of different mechanisms, both direct and indirect. Against this background of increased risk, the diagnosis of ischaemic stroke potentially encompasses five pathophysiological categories: those due to thrombosis in situ (29-44%); cardio-embolism (20-25%); small artery disease or lacunar strokes (13-21%); and those due to mixed or undetermined aetiologies (15-17%) (Adams etal., 1993).
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