Prevalence Of Impaired Awareness Of Hypoglycaemia

Impaired awareness of hypoglycaemia is common in people treated with insulin. Although the chronic form of this acquired condition mainly affects those with type 1 diabetes, it appears that a similar problem does eventually emerge in patients with type 2 diabetes who have been treated with insulin for several years (Hepburn et al., 1993a). A prevalence of 8% was observed in a cohort of 215 patients in Edinburgh (Henderson et al., 2003). Because few patients with type 2 diabetes who require insulin therapy survive for a sufficiently long period to permit this complication to develop, impaired awareness is principally a problem associated with type 1 diabetes. It is not known whether impaired awareness of hypoglycaemia occurs in diabetic patients treated with oral antidiabetic agents.

Impaired awareness of hypoglycaemia has been shown to be associated with strict glycaemic control (see Chapter 8), but significant modification of the symptomatic response to hypoglycaemia does not occur unless the glycated haemoglobin concentration is within the non-diabetic range (Boyle et al., 1995; Kinsley et al., 1995; Pampanelli et al., 1996). Only a small proportion of people with insulin-treated diabetes can sustain this degree of super-optimal glycaemic control indefinitely. In the Diabetes Control and Complications Trial (DCCT), with its extensive resources devoted to maintaining intensive insulin therapy, more than 40% of the patients in the group with strict glycaemic control achieved a HbA1c of 6.05% or less (the upper limit of the non-diabetic range) at some time during the study, but only 5% were able to maintain this level of glycaemic control continuously (The Diabetes Control and Complications Trial Research Group, 1993). The proportion of any insulin-treated diabetic population that can achieve this therapeutic goal will depend on local policies regarding insulin therapy, the expertise of local diabetes specialist teams, available resources and the enthusiasm of individual patients. With the exception of a few highly motivated patients, most people treated with insulin are unable to maintain strict glycaemic control for protracted periods. In clinical practice this 'acute' form of hypoglycaemia unawareness is probably relatively uncommon. Nonetheless, the influence of strict glycaemic control on symptomatic and counterregulatory responses to hypoglycaemia has been studied extensively, and has provided insights into the potential pathogenetic mechanisms underlying impaired awareness of hypoglycaemia.

Reduced warning symptoms of hypoglycaemia (of varying severity) occur in approximately one quarter of all insulin-treated patients. Cross-sectional population surveys in different European and North American populations of insulin-treated diabetic patients, using similar methods of assessment, have given remarkably consistent estimates (Table 7.1). Impaired awareness of hypoglycaemia becomes more common with increasing duration of insulin-treated diabetes (Hepburn et al., 1990), and almost 50% of patients experience hypoglycaemia without warning symptoms after 25 years or more of treatment (Pramming et al., 1991) (Figure 7.3). It appears therefore to be an acquired abnormality associated with insulin therapy.

Table 7.1 Prevalence of Hypoglycaemia Unawareness in population studies of insulin-treated diabetes

Country

Number of patients

Impaired awareness of hypoglycaemia (%)

Reference

Scotland Germany Denmark USA

302 523 411 628

23 25 27 20

Hepburn et al. (1990) Muhlhauser et al. (1991) Pramming et al. (1991) Orchard et al. (1991)

Figure 7.3 Comparisons between the duration of diabetes and the percentage of 411 type 1 diabetic patients reporting (a) changes in symptoms of hypoglycaemia, (b) sweating and/or tremor as one of the two cardinal autonomic symptoms of hypoglycaemia, and (c) severe hypoglycaemic episodes without warning symptoms. Values are medians; shaded areas show 95% confidence limits. Reproduced from Pramming et al. (1991) by permission of John Wiley & Sons, Ltd

Figure 7.3 Comparisons between the duration of diabetes and the percentage of 411 type 1 diabetic patients reporting (a) changes in symptoms of hypoglycaemia, (b) sweating and/or tremor as one of the two cardinal autonomic symptoms of hypoglycaemia, and (c) severe hypoglycaemic episodes without warning symptoms. Values are medians; shaded areas show 95% confidence limits. Reproduced from Pramming et al. (1991) by permission of John Wiley & Sons, Ltd

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