Hypoglycaemia in Clinical Diabetes

286 LONG-TERM EFFECTS OF HYPOGLYCAEMIACOGNITIVE FUNCTION AND HYPOGLYCAEMIAHypoglycaemia and Mental Functions in Children and AdolescentsThere is controversy about whether repeated episodes of severe hypoglycaemia have lastingeffects on the thinking skills of children (Ryan et al., 2005). In addition to the severity ofhypoglycaemia, the age of the individual is important in determining the potential impact ofhypoglycaemia on the brain (Ack et al., 1961). The human brain develops rapidly until theage of five years, and during this critical period any insult can have long-lasting effects. Indiabetic children important risk factors for the development of later cognitive impairmentare as follows (Ryan, 1988; 1997):• early onset of diabetes;• long duration of diabetes;• poor metabolic control;• severe hypoglycaemia.Children with type 1 diabetes who suffer repeated and severe hypoglycaemia whileyounger than five years old have lower mental abilities later on in life, and may show moredifficult behaviour (Ryan et al., 1984; Rovet et al., 1987; Golden et al., 1989; Hersheyet al., 2005; Ryan et al., 2005). The combination of an early onset of diabetes (before fiveyears of age) and recurrent severe hypoglycaemia appears to be associated with reducedattention, psychomotor efficiency, and spatial memory in adolescence (Rovet and Alvarez,1997; Bjorgaas et al., 1997; Hershey et al., 2005). Adolescents who had developed type1 diabetes after the age of five years have been shown to have lower verbal IQ than theirpeers, but this may be related in part to learning-related problems at school and loss offormal education rather than with hypoglycaemia (Fallstrom, 1974; Ryan et al., 2005).Most of the studies mentioned above are cross-sectional, that is, they have tested groups ofchildren, with and without diabetes, and have tried to review the children’s clinical recordsto estimate the amount of previous hypoglycaemia experienced by each child with diabetes.A more robust type of study is one in which groups of children are followed prospectively.One such study is ongoing in Melbourne, Australia (Northam et al., 1995). Over 100 childrenwith newly diagnosed type 1 diabetes have been compared with a matched control group ofnon-diabetic children. No differences in mental abilities or in educational attainments werediscernible between the two groups. Therefore, when children develop type 1 diabetes they donot begin with any mental decrements when they are compared with their non-diabetic peers.An initial report from this invaluable study indicated that within two years of the developmentof diabetes the mental abilities of the diabetic children may begin to lag behind their nondiabeticpeers (Northam et al., 1998). Six years after diagnosis, diabetic children performedworse than non-diabetic controls across a range of cognitive performance tests, while severehypoglycaemia was associated with poorer verbal and IQ scores (Northam et al., 2001).However, the roles of hyper- and hypoglycaemia and other possible effects of having diabetesin promoting these changes, such as increased school absence, remain to be elucidated.Another study of 41 children with early onset (< 6 years) type 1 diabetes found noassociation between severe hypoglycaemia and cognition (Strudwick et al., 2005). Theirepisodes of severe hypoglycaemia were recorded prospectively and their scores on IQ,