New Findings on Diabetes and Cognitive Impairment

 Studies show that patients with type 2 diabetes are more likely to exhibit reduced cognitive function after a stroke.  

Numerous studies have proven type 2 diabetes increases the risk of developing neurogenerative diseases. Strong pathophysiologic evidence has linked type 2 diabetes to the progressive development of dementia and overall poorer cognition. When looking specifically at cognitive impairment after stroke, discrepancies from studies have made it unclear whether prediabetes or type 2 diabetes is the dominant factor. This Stroke and Cognition (STOKOG) Collaboration study by Lo et al. looks closely at prediabetes, or impaired fasting glucose (IFG), and type 2 diabetes to determine which causes worse cognitive function in patients 3 to 6 months after stroke. 

Recruited patients in this study had been consecutively admitted to hospitals due to stroke. In this environment, they were also given neuropsychological tests that assessed one of five domains: attention and processing speed, memory, language, perceptual-motor, and executive function. These tests were converted into Z scores, and further into a global cognition score as the standardized average. As far as the diagnosis of diabetes and prediabetes, patients were assigned to one of three glucose status groups: type 2 diabetes, IFG, and normal fasting glucose levels (FGL). Based on the World Health Organization criteria, type 2 diabetes was defined as having a fasting blood glucose of 126mg/dL or more, having an established diagnosis of diabetes, or using diabetic medications. IFG, or prediabetes, was defined as having an FGL between 110 and 125mg/dL, and normal FGL was having less than 110mg/dL. The analysis also included HbA1c levels as defining criteria—a reading of 6.5% or greater equated to diabetes and between 5.7% and 6.5% represented prediabetes. ANOVA and Pearson Chi-Square Tests were used to compare statistical significance within the baseline characteristics of patients. Differences between stroke characteristics, vascular risk factors, and background variables were analyzed. To further examine the link between the cognitive scores and glucose status, researchers used linear mixed models. The effect of hyperglycemia was additionally tested as being a function of a stress response poststroke. 

Once categorized, 36% of patients were grouped as having type 2 diabetes, 12% had IFG, and 52% were considered normal. From the findings of the mixed models, patients with type 2 diabetes had a significant cognitive decline in global cognition as well as the five domains compared to patients with normal FGL. This group had more than half a standard deviation (SD) lower Z scores (SD, -0.59 [95% CI, -0.82 to -0.36]; P<0.001) compared to the standard FGL group. The particular domains that showed the most deficiency in type 2 diabetes patients were attention and processing speed, which had an average of 0.54 SD lower than those with normal FGL and perceptual–motor (SD, -.039), followed by executive function (SD -0.36). A similar study also found that type 2 diabetes was associated with lower Mini-Mental State Examination scores, a test widely used for assessing cognitive function in patients with an ischemic stroke one week after admission. Another study revealed that patients who have experienced a stroke and had depression and diabetes had a higher risk of developing severe cognitive impairment based on the Montreal Cognitive Assessment (MoCA), a test designed to detect mild cognitive impairment and Alzheimer’s Disease. This collaborative study contributed more findings by examining FGL and not just medical history. In contrast, patients in the IFG group did not show any significant differences in the five-domain neuropsychological test compared to the healthy group. Only small effects were shown within the memory, language, and perceptual-motor components of the test for these patients. 

This study suggests that patients with type 2 diabetes and stroke may experience more cognitive impairment than those with prediabetes, and may even be at a higher risk of developing dementia. Researchers, however, were unable to assess the impact of the duration and severity of type 2 diabetes on cognitive function due to limited diabetes data, measuring FGL at one point in time, and a lack of specifics on the diabetic medications that were used by patients. The study’s limitations also arose due to the fact of being cross-sectional, which may have raised the possibility of patients with type 2 diabetes experiencing cognitive deficiencies before the stroke. Overall, the results of this study are indicative of significant implications for the care of patients with type 2 diabetes after stroke. The attentiveness needed to monitor glucose levels, handle monitoring devices, and administer complex medication regimens is compromised when patients begin to experience cognitive deficiency. From this, it is essential to assess the mental function of patients with diabetes post-stroke to determine whether they are able to conduct these tasks, and to determine if their routines should be simplified. 

Practice Pearls: 

• Patients with type 2 diabetes who have experienced a stroke had higher cognitive deficiency results than those with normal FGL. 
• Patients with IFG, or prediabetes, showed no significant difference within the five domains compared to patients with normal FGL. 
• Mental function of patients with type 2 diabetes post-stroke should be evaluated to assess self-care capabilities and the need for simplification. 

Lo, Jessica W. et al. “Association of Prediabetes and Type 2 Diabetes With Cognitive Function After Stroke.” Stroke, vol. 51, no. 6, 2020, pp. 1640–1646., doi:10.1161/strokeaha.119.028428. 

Maya Palmer, PharmD. Candidate, Florida A&M University College of Pharmacy 

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