Cognitive Impairment Seen in Adults With Type 1 Diabetes

Miriam E Tucker

July 16, 2015

Clinically relevant cognitive impairment is present in over a quarter of middle-aged adults who had been diagnosed with type 1 diabetes in childhood, a new study finds.

The results were published online July 7, 2015 in Diabetes Care by Karen A Nunley, PhD, a postdoctoral associate in epidemiology at the University of Pittsburgh, Pennsylvania, and colleagues.

Extensive neuropsychiatric testing among 97 adults with a mean age of 49 years who had been diagnosed with type 1 diabetes in childhood revealed a 28% prevalence of clinically relevant cognitive impairment, which is comparable to the prevalence of mild cognitive impairment typically reported in adults aged 85 years and older.

The finding raises several concerns, Dr Nunley told Medscape Medical News.

"We are studying adults who were all diagnosed in childhood, whereas previous studies included individuals diagnosed in adulthood, people who were not exposed to diabetes-related metabolic dysregulation during crucial periods of brain development that occurs during childhood."

And, she pointed out, the subjects are also middle-aged adults "who are at risk of experiencing 'normal' age-related cognitive changes, the effects of which may be amplified by long-term exposure to diabetes."

One explanation could be that chronic hyperglycemia has negative effects on cerebral vasculature, similar to that known to occur in the retina or kidney, she said.

And one key concern is that the cognitive impairment may affect the patient's ability to manage their own diabetes. Poor executive function could hinder time management, the ability to plan and organize, to remember details, and to switch focus, Dr Nunley said, adding also that impaired psychomotor speed could affect the patient's ability to respond quickly to a dangerous situation — for example, while driving.

However, she also stressed, "We are in no way implying that people with childhood-onset type 1 diabetes cannot become successful adults with important careers. What we hope to do is raise awareness that cognitive impairment is a potential complication of diabetes, along the lines of retinopathy and neuropathy, so medical providers can help those with type 1 and their caregivers understand why this happens."

Cognitive Impairment Increased Fivefold

The 97 adults with childhood-onset type 1 diabetes were compared with 138 age-matched adults without diabetes on a series of cognitive tests, including those that measure estimated verbal intelligence, psychomotor efficiency, executive function, verbal fluency, learning and working memory, and visuoconstruction skills.

Those with type 1 diabetes were five times more likely to have impairment on two or more tests, meeting the definition of "clinically relevant cognitive impairment," than those without diabetes (28% vs 5%, P < .0001), and this effect was still evident even after adjustment for education.

Excluding patients with hypertension also did not significantly change the relationship between type 1 diabetes and cognitive impairment (odds ratio, 4.35; P = .001).

Among the subjects with type 1 diabetes, a 14-year (1996–2013) average HbA1c of 7.5% or greater tripled the odds of cognitive impairment, while each unit increase in body mass index (BMI) raised the risk by 10%. And an average ankle-brachial index of greater than 1.3/noncompressible quadrupled the risk of cognitive impairment.

Dr Nunley told Medscape Medical News that the 7.5% threshold for HbA1c was chosen because this value is used in a number of published articles, and a level greater than 7.5% is related to higher rates of diabetes-related complications and other poor outcomes.

"If we are able to complete cognitive testing in a larger sample size, we will then assess whether there is a linear association between cognitive impairment and HbA1c as a continuous measure," she noted.

Physicians Should Assess Type 1 Diabetics for Cognition

Dr Nunley said her group recommends that clinicians ask patients with type 1 diabetes about their self-perceived mental/cognitive functioning at each visit. The information could also be supported/confirmed by someone else, such as a spouse, parent, child, or other person familiar with the patient's cognitive function over time.

If the patient reports difficulty remembering details or concentrating or just reports a "mental fog," then a cognitive test battery may be in order.

There are also brief cognitive assessments — such as the Montreal Cognitive Assessment or the Modified Mini-Mental Exam — that could be given periodically, starting in early adulthood. "Clinicians might thereby detect early changes in cognitive function, perhaps before the patient even notices, allowing for early interventions aimed to preserve cognitive function," she explained.

Ultimately, she told Medscape Medical News, "We hope to remove the fear or embarrassment associated with talking about changes in cognitive function, because in some cases it can be reversed — for example, if it is related to a particular medication or depression.

"Our ultimate goal is to provide information that will help identify targets/strategies that either prevent the development of or at least minimize the severity of cognitive impairment in people with type 1 diabetes."

This study received support from the National Institutes of Health. None of the authors report relevant financial relationships.

Diabetes Care. Published online July 7, 2015. Abstract

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