QUEBEC CITY — Magnetic resonance imagery and spectroscopy of the brain show decreased hippocampal volume in children with type 1 diabetes, and evidence of neuronal damage in a subgroup of those children who have hypoglycemic seizures, according to a new study.
These findings coincide with another study of children with type 1 diabetes, showing deficits in memory that are specifically tied to the hippocampal region, reported researchers from York University in Toronto.
“The hippocampus is quite sensitive to fluctuations in glucose, and also has a high number of insulin receptors—so if there is too much insulin, this can have an impact on functioning,” said Mary Desrochers, Ph.D., who supervised both studies. The results were presented as posters at the joint annual meeting of the Canadian Diabetes Association and the Canadian Society of Endocrinology and Metabolism.
The first study included 10 children with type 1 diabetes (aged 10–14 years, with an age of onset of less than 5 years), half of whom had severe hypoglycemic episodes. They were age-matched to 10 healthy controls.
MRI showed that all patients with diabetes had smaller hippocampal volumes than did controls. And MRI spectroscopy showed elevated levels of inositol and glutamate, suggestive of neuronal damage, in children with a history of hypoglycemic seizures.
“This tells us that overcontrol of hyperglycemia is possibly an issue,” Dr. Desrochers told this newspaper. “All of the children in this study had excellent glycemic control and some of the parents told us that they sometimes give their children extra injections of insulin. So that would be something to look into—whether overcontrol is playing a role in the incidence of hypoglycemic seizures.”
The study also looked at the neuropsychological functioning of the children and found a trend toward long-term (explicit) memory deficits associated with type 1 diabetes specifically in the areas of verbal and visual memory, functions that are controlled by the hippocampus. However, more conclusive evidence for memory deficits came from a separate study.
In that study, conducted by Ph.D. candidate Lila Elkhadem, explicit and implicit memory skills were compared in 15 children with type 1 diabetes and 17 healthy controls (mean age between 11 and 12 years).
Explicit memory is actively learned whereas implicit memory is information that is more passively absorbed, explained Dr. Desrochers.
“Implicit memory develops earlier and remains robust throughout life. It is what is learned every day, whereas explicit memory is involved when you tell someone they need to remember something,” she said.
The study found that in children with diabetes, implicit memory did not differ from controls, but explicit memory was affected.
“They remembered fewer words and fewer themes in stories, as well as fewer numbers in a digit span test,” Dr. Desrochers said. She added that there were some less significant problems with visual memory.
The study also examined the relationship between memory and both blood glucose fluctuations during the day and duration of diabetes. It found that children with more variation in their blood glucose levels performed worse on almost all types of memory tests, compared with children with more stable blood glucose levels. And longer duration of diabetes was associated with poorer performance.
Finally, the study also found that memory in children with diabetes was also affected by time of day—with significantly better performances noted in the morning.
The findings have implications for how children with type 1 diabetes should be scheduled and taught in school.