Hypoglycaemia in Clinical Diabetes

PATHOGENESIS OF IMPAIRED AWARENESS OF HYPOGLYCAEMIA 149Frequency of Associated Severe HypoglycaemiaIt is apparent that impaired awareness of hypoglycaemia is a major risk factor for severehypoglycaemia. In the DCCT, 36% of all episodes of severe hypoglycaemia occurred withno warning symptoms in patients while they were awake (The DCCT Research Group,1991). In a population study in Edinburgh, retrospective assessment of the frequency ofsevere hypoglycaemia revealed that 90% of patients with impaired awareness of symptomsexperienced severe hypoglycaemia in the preceding year, compared to 18% in a comparablegroup who had retained normal awareness (Hepburn et al., 1990). Prospective studies haveconfirmed the increase in frequency of mild and severe hypoglycaemia associated withimpaired awareness of hypoglycaemia (Gold et al., 1994; Clarke et al., 1995), with a sixfoldhigher frequency of severe hypoglycaemia being documented in people with impairedawareness (Gold et al., 1994) (Figure 7.4).Annual Prevalence(% Subjects)Incidence(Events per subject per year)Figure 7.4 Proportion of patients affected and event rates for severe hypoglycaemia in patientswith type 1 diabetes with normal (□, n= 31) or impaired (, n= 29) awareness of hypoglycaemia.Reproduced from Cryer and Frier (2004) by permission of John Wiley & Sons, Ltd. Data derived fromGold et al. (1994)PATHOGENESIS OF IMPAIRED AWARENESS OFHYPOGLYCAEMIAThe mechanisms underlying impaired awareness of hypoglycaemia are not known and maybe multifactorial. Possible mechanisms are listed in Box 7.2.