Elsevier

The Lancet Neurology

Volume 14, Issue 3, March 2015, Pages 329-340
The Lancet Neurology

Personal View
Cognitive function in patients with diabetes mellitus: guidance for daily care

https://doi.org/10.1016/S1474-4422(14)70249-2Get rights and content

Summary

Diabetes mellitus is associated with an increase in the risk of dementia and the proportion of patients who convert from mild cognitive impairment (MCI) to dementia. In addition to MCI and dementia, the stages of diabetes-associated cognitive dysfunction include subtle cognitive changes that are unlikely to affect activities of daily life or diabetes self-management. These diabetes-associated cognitive decrements have structural brain correlates detectable with brain MRI, but usually show little progression over time. Although cognitive decrements do not generally represent a pre-dementia stage in patients below the age of 60–65 years, in older individuals these subtle cognitive changes might represent the earliest stages of a dementia process. Acknowledgment of diabetes-associated cognitive decrements can help to improve understanding of patients' symptoms and guide management. Future challenges are to establish the importance of screening for cognitive impairment in people with diabetes, to identify those at increased risk of accelerated cognitive decline at an early stage, and to develop effective treatments.

Introduction

Diabetes mellitus is a common metabolic disorder that can lead to chronic complications such as cardiovascular disease, nephropathy, retinopathy, and peripheral neuropathy. Both type 1 and type 2 diabetes are characterised by hyperglycaemia, but their pathophysiology, associated comorbidities, and epidemiology are different (table 1). Type 1 diabetes accounts for 5–10% of diabetes cases and mostly develops in childhood or early adulthood.1 Type 2 diabetes is caused by insulin resistance, which is often related to obesity, but also involves progressive β-cell dysfunction.2 Type 2 diabetes is typically a disease of older age, although its incidence has increased in young adults and even in adolescents during the past two decades.3 The worldwide prevalence of diabetes has increased during the past five decades, with 382 million people with diabetes in 2013, and is likely to increase further, making diabetes and its complications important public health issues.4

Awareness is increasing of subtle structural and functional cerebral changes in patients with diabetes, which can manifest in cognitive dysfunction. This increasing awareness is shown by a steady increase in publications about topics ranging from detailed cognitive testing and advanced brain imaging to epidemiological surveys. However, little guidance is available for the application of available knowledge about the daily clinical management of cognitive dysfunction in patients with diabetes. In this Personal View, we provide a framework that links different stages of cognitive dysfunction in type 1 and type 2 diabetes with brain-imaging abnormalities, risk factors, and treatment options. Additionally, we address the issues surrounding early identification of patients at increased risk of accelerated cognitive decline, and suggest possible therapeutic approaches.

Section snippets

Cognitive function

Neuropsychological studies in patients with type 1 diabetes consistently report subtle changes in cognitive function compared with individuals without diabetes, particularly in general intelligence, psychomotor speed, and mental flexibility. In a systematic review,5 performance on these domains in adult patients was on average half an SD (0·3–0·7 SDs) below that of people without diabetes. Additionally, overall cognition and the visual perception domain were slightly affected (0·3–0·4 SDs less

Cognitive function

Compared with people without diabetes, patients with type 2 diabetes perform slightly worse on a range of cognitive tasks. For memory, processing speed, and executive function, cognitive performance is on average 0·3–0·4 SDs lower than that of people without diabetes.24, 25 These subtle changes in cognitive performance have been reported from adolescence26 up to the age of 80 years (figure 1). Because several domains are affected in patients with type 2 diabetes, a diminished ability to

Classification of stages of cognitive dysfunction

The data discussed in the preceding sections show that diabetes is associated with changes in cognitive function, ranging from subtle cognitive changes to MCI and dementia. In our view, differentiation between these different stages of cognitive dysfunction in clinical practice is essential, because they are likely to have a different prognosis and might need different management (panel 1).6

The same diagnostic criteria apply to cognitive impairment—ie, MCI and dementia—in people with diabetes

Cognitive impairment

No specific treatments exist for people with diabetes and MCI or dementia, and clinicians should treat MCI or dementia according to the same principles as in people without diabetes. Nevertheless, cognitive dysfunction in patients with diabetes is associated with poor glycaemic control93—especially in the case of impaired executive function94—with an increased frequency of hospital admissions and with an increased occurrence of severe hypoglycaemic episodes.72 Therefore, diagnosis of cognitive

Future perspectives

Awareness of diabetes-associated cognitive dysfunction is increasing. However, important questions still need to be answered. Should cognitive impairment be routinely screened for in patients with diabetes, just like other diabetic complications? Can people at risk of accelerated cognitive decline be identified at an early stage, and how should these people be treated to prevent deterioration?

Conclusions

Diabetes is linked to different stages of cognitive dysfunction, ranging from diabetes-associated cognitive decrements to dementia. These stages are not necessarily part of one continuous process, and might have different prognoses. Moreover, different stages need different management. We present a framework that helps to distinguish between different stages of cognitive dysfunction in patients with diabetes. No treatment exists to reduce or prevent diabetes-associated cognitive dysfunction,

Search strategy and selection criteria

We searched PubMed from Jan 1, 1990, to May 15, 2014, with the terms (and synonyms) “dementia”, “Alzheimer's disease”, “cognitive impairment”, “diabetes”, and “metabolic syndrome”, in combination with the key terms “epidemiology”, “risk factors”, “brain MRI”, “prevention”, “diagnosis”, “treatment”, and “screening”. We only searched for papers published in English. We also searched reference lists of papers identified and extracted relevant papers from our records. Furthermore, we searched //ClinicalTrials.gov

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