Memory dysfunction and autonomic neuropathy in non-insulin-dependent (type 2) diabetic patients

Changes in the central nervous system in diabetic neuropathy

One of the most common chronic complications arising from diabetes is diabetic peripheral neuropathy. Depending on research statistics, approximately half of the people who have diabetes will suffer from diabetic peripheral neuropathy over time, which manifests as abnormal sensations in the distal extremities, and about 25%-50% of these patients have symptoms of neuralgia, called painful diabetic neuropathy. These patients often exhibit adverse emotional conditions, like anxiety or depression, which can reduce their quality of life. The pathogenesis of diabetic peripheral neuropathy is complex, and although persistent hyperglycemia plays a central role in the development of diabetic peripheral neuropathy, strict glycemic control does not eliminate the risk of diabetic peripheral neuropathy. This suggests the need to understand the role of the central nervous system in the development of diabetic peripheral neuropathy to modulate treatment regimens accordingly. Magnetic resonance imaging not only allows for the noninvasive detection of structural and functional alterations in the central nervous system, but also provides insight into the processing of abnormal information such as pain by the central nervous system, and most importantly, contributes to the development of more effective pain relief protocols. Therefore, this article will focus on the mechanisms and related imaging evidence of central alterations in diabetic peripheral neuropathy, especially in painful diabetic neuropathy.

The cross-sectional association of cognition with diabetic peripheral and autonomic neuropathy-The GRADE study

BACKGROUND

Studies examining whether measures of cognition are related to the presence of diabetic peripheral neuropathy (DPN) and/or cardiovascular autonomic neuropathy (CAN) are lacking, as are data regarding factors potentially explaining such associations.

METHODS

Participants were from the Glycemia Reduction Approaches in Diabetes Study (GRADE) that examined 5047 middle-aged people with type 2 diabetes of <10 years of known duration. Verbal learning and immediate and delayed recall (memory) were assessed with the Spanish English Verbal Learning Test; frontal executive function and processing speed with the Digit Symbol Substitution Test; and ability to concentrate and organize data with word and animal fluency tests. DPN was assessed with the Michigan Neuropathy Screening Instrument and CAN by indices of heart rate variability (standard deviation of normal beat to beat variation [SDNN] and root mean square of successive differences [RMSSD]).

RESULTS

DPN was significantly inversely related to measures of immediate recall and processing speed. The percent of cognitive variation explained by DPN was small. Tests of CAN had an inconsistent or absent association with measures of cognition. Higher waist circumference and urine albumin creatinine (UACR) levels were the strongest correlates in the relationship between DPN and cognitive impairment.

CONCLUSION

DPN, but not CAN, was cross-sectionally associated with lower performance in measures of cognition in people with type 2 diabetes of <10 years of known duration. Greater waist circumference and UACR were important variables in this association. The mechanisms underlying the cross-sectional association of DPN with cognitive impairment are unknown. Clinicaltrials.gov: NCT01794143.

Glucose regulation and face recognition deficits in older adults: the role of attention

The present study investigated the perceptual, attentional, and memory processes underlying face recognition deficits observed in older adults with impaired glucoregulation. Participants were categorized as good glucoregulators or poor glucoregulators on the basis of an oral glucose tolerance test. Using event-related potential (ERP) methodology, 23 participants (62-88 years) performed a 2-stimulus oddball task. Participants were asked to rate and memorize 10 "target" faces, which were then presented amongst 120 unfamiliar foils. Behavioral results indicated that good glucoregulators were significantly more accurate at recognizing target faces. ERP markers of early visual perception (P1 and N170 components) and memory formation (P3 component) were unaffected by glucoregulatory efficiency. The P2 component, an index of attentional processing, was larger and delayed in the poor glucoregulators. To the best of our knowledge, this study is the first to suggest that face recognition deficits in poor glucoregulators may be due to impairments in attentional processing.

Impaired Word and Face Recognition in Older Adults with Type 2 Diabetes

BACKGROUND AND AIMS

Older adults with type 2 diabetes mellitus (DM2) exhibit accelerated decline in some domains of cognition including verbal episodic memory. Few studies have investigated the influence of DM2 status in older adults on recognition memory for more complex stimuli such as faces. In the present study we sought to compare recognition memory performance for words, objects and faces under conditions of relatively low and high cognitive load.

METHODS

Healthy older adults with good glucoregulatory control (n = 13) and older adults with DM2 (n = 24) were administered recognition memory tasks in which stimuli (faces, objects and words) were presented under conditions of either i) low (stimulus presented without a background pattern) or ii) high (stimulus presented against a background pattern) cognitive load.

RESULTS

In a subsequent recognition phase, the DM2 group recognized fewer faces than healthy controls. Further, the DM2 group exhibited word recognition deficits in the low cognitive load condition.

CONCLUSIONS

The recognition memory impairment observed in patients with DM2 has clear implications for day-to-day functioning. Although these deficits were not amplified under conditions of increased cognitive load, the present study emphasizes that recognition memory impairment for both words and more complex stimuli such as face are a feature of DM2 in older adults.

Diabetes and Cognitive Impairment

Both type 1 (T1DM) and type 2 diabetes mellitus (T2DM) have been associated with reduced performance on multiple domains of cognitive function and with evidence of abnormal structural and functional brain magnetic resonance imaging (MRI). Cognitive deficits may occur at the very earliest stages of diabetes and are further exacerbated by the metabolic syndrome. The duration of diabetes and glycemic control may have an impact on the type and severity of cognitive impairment, but as yet we cannot predict who is at greatest risk of developing cognitive impairment. The pathophysiology of cognitive impairment is multifactorial, although dysfunction in each interconnecting pathway ultimately leads to discordance in metabolic signaling. The pathophysiology includes defects in insulin signaling, autonomic function, neuroinflammatory pathways, mitochondrial (Mt) metabolism, the sirtuin-peroxisome proliferator-activated receptor-gamma co-activator 1α (SIRT-PGC-1α) axis, and Tau signaling. Several promising therapies have been identified in pre-clinical studies, but remain to be validated in clinical trials.

Glucose regulation, cognition, and brain MRI in type 2 diabetes: a systematic review

Type 2 diabetes is associated with cognitive dysfunction and structural brain changes. Abnormalities in glucose regulation are involved in several complications related to type 2 diabetes, but their role in these cerebral complications is unclear. We systematically reviewed studies of the association between glucose regulation (glycaemia, hypoglycaemic events, insulin concentration, insulin resistance, and glucose-lowering treatment) and cognitive function and brain abnormalities on MRI in people with type 2 diabetes. The 86 papers included showed that glycaemia, particularly high HbA1c concentration and glucose variability, are negatively associated with cognitive function in people with type 2 diabetes without dementia. However, the strength of this association is weak, and HbA1c generally accounted for less than 10% of the variance in cognition. Importantly, few studies have measured long-term cerebral outcomes, such as dementia and structural brain changes on MRI, and the effect of glucose-lowering treatment on these outcomes. More randomised controlled trials are needed to establish the effect of glucose-lowering treatment on long-term cognitive function in people with type 2 diabetes.

Exercising with peripheral or autonomic neuropathy: what health care providers and diabetic patients need to know

Both peripheral and autonomic neuropathies are characterized by a progressive loss of nerve fiber function. Most peripheral neuropathy affects the extremities, particularly the lower legs and the feet, but also the hands, whereas damage to the autonomic nervous system may lead to imbalances between the sympathetic and parasympathetic nerve fibers that innervate the heart and blood vessels, as well as abnormalities in heart rate control and vascular dynamics. To prescribe or engage in exercise that is both safe and effective, health care providers and patients with diabetes mellitus need to increase their understanding of the pathophysiological nature of neuropathies and the physical activity hurdles that may arise from the presence of a neuropathy. With proper care and preventative measures, patients with diabetes mellitus that experience either type of neuropathy can benefit from regular participation in mild to moderate aerobic, resistance, and balance activities, assuming they take any potential alterations into account to ensure that exercise is safe and effective.

Peripheral and central neurologic complications in type 2 diabetes mellitus: No association in individual patients

Diabetes mellitus is associated with end-organ complications in the peripheral and central nervous system. It is unknown if these complications share a common aetiology, and if they co-occur in the same patient. The aim of the present study was to relate different measures of peripheral neuropathy in patients with type 2 diabetes mellitus (DM2) to cognition and brain MRI. A standardized neurological examination and questionnaire, neuropsychological examination and brain MRI were performed in 122 patients with DM2 and 56 matched controls. Measures of peripheral neuropathy were vibration threshold, a sensory examination sum score and the Toronto Clinical Neuropathy Scoring System. Neuropsychological test scores were expressed in standardized z-values across five predetermined cognitive domains. White matter lesions and cortical and subcortical atrophy were rated on MRI. Overall 38% of the patients with DM2 and 12% of the controls were classified as having any neuropathy (p<0.001). Patients with DM2 had a lower performance on the neuropsychological tests, more white matter lesions (p<0.01) and more atrophy (p<0.01) than controls. Within the DM2 group none of the measures of peripheral neuropathy was related to MRI abnormalities or cognitive dysfunction (linear regression analyses, adjusted for age, education, sex). We conclude that peripheral neuropathy in patients with DM2 is not related to cognitive dysfunction and brain abnormalities. This indicates that central and peripheral neurological complications of DM2 might have different etiologies.

Metabolic and vascular determinants of impaired cognitive performance and abnormalities on brain magnetic resonance imaging in patients with type 2 diabetes

AIMS/HYPOTHESIS

The determinants of cerebral complications of type 2 diabetes are unclear. The present study aimed to identify metabolic and vascular factors that are associated with impaired cognitive performance and abnormalities on brain MRI in patients with type 2 diabetes.

METHODS

The study included 122 patients and 56 controls. Neuropsychological test scores were divided into five cognitive domains and expressed as standardised z values. Brain MRI scans were rated for white matter lesions (WML), cortical and subcortical atrophy, and infarcts. Data on glucose metabolism, vascular risk factors and micro- and macrovascular disease were collected.

RESULTS

Patients with type 2 diabetes had more cortical (p < 0.001) and subcortical (p < 0.01) atrophy and deep WML (p = 0.02) than the control group and their cognitive performance was worse. In multivariate regression analyses within the type 2 diabetes group, hypertension (p < 0.05) and a history of vascular events (p < 0.01) were associated with worse cognitive performance, while statin use was associated (p < 0.05) with better performance. Retinopathy and brain infarcts on MRI were associated with more severe cortical atrophy (both p < 0.01) and statin use with less atrophy (p < 0.05). Insulin level and brain infarcts were associated with more severe WML and statin use with less severe WML (all p < 0.05).

CONCLUSIONS/INTERPRETATION

Type 2 diabetes is associated with modest impairments in cognition, as well as atrophy and vascular lesions on MRI. This 'diabetic encephalopathy' is a multifactorial condition, for which atherosclerotic (macroangiopathic) vascular disease is an important determinant. Chronic hyperglycaemia, hyperinsulinaemia and hypertension may play additional roles.

The relationship between impaired glucose tolerance, type 2 diabetes, and cognitive function

The present review integrates findings of published studies that have evaluated the cognitive function of treated and untreated type 2 diabetic patients and provides a detailed overview of the neuropsychological assessments conducted. Cognitive deficits are observed in older people with glucose intolerance or untreated diabetes but these deficits appear to be attenuated by treatments that improve glycemic control. Cognitive decrements in treated type 2 diabetic patients are most consistently observed on measures of verbal memory (35% of the measures) and processing speed (45% of the measures) while preserved function is observed on measures of visuospatial, attention, semantic and language function. Some studies suggest that deficits in cognitive functions are associated with poorer glycemic control. A number of other factors, such as depression, cardiovascular and cerebrovascular disease, increase these deficits. We conclude that, in diabetic patients who achieve and maintain good glycemic control, type 2 diabetes only has a small impact on cognitive functions before the age of 70 years. However, early onset of type 2 diabetes, poor glycemic control and the presence of micro- and macrovascular disease may interact to produce early cognitive deficits. In older adults (70 years and over), diabetes likely interacts with other dementing processes such as vascular disease and Alzheimer's disease to hasten cognitive decline.

The relationships between atherosclerosis, heart disease, type 2 diabetes and dementia

Type 2 diabetes in the elderly is associated with increased incidence of vascular disease, particularly, atherosclerosis of large blood vessels. Together with other risk factors such as dyslipidemia, atherosclerosis increases the risk for coronary heart disease and stroke. Most studies that have examined the impact of type 2 diabetes and other heart disease risk factors on cognitive functions do not provide evidence that heart disease risk factors (with the possible exception of triglycerides) further increase the likelihood of observing cognitive deficits in diabetic patients. However, none of these studies used imaging techniques to evaluate atherosclerosis or evidence of cerebrovascular disease, such as infarctions. The few studies that have included brain imaging suggest that evidence of cerebrovascular disease further increases the risk for dementia in diabetic patients. The results of longitudinal studies suggest that diabetes is an independent risk factor for cognitive decline and dementia. The pattern of neuropsychological performance observed in type 2 diabetic patients appears to be the result of multiple interacting processes developing over time. In addition to the detrimental effects of protracted impaired glucose regulation on the central nervous system, type 2 diabetes pathology also encompasses the detrimental effects of associated complications such as cerebrovascular disease, which is likely the main cause of the observed processing speed/reaction time decrements.

Type 2 diabetes mellitus and cognition: an understudied issue in women's health

INTRODUCTION

Diabetes is a common chronic illness, affecting approximately 16 million Americans, and is slightly more common in women than men. Data from population studies demonstrate that women with diabetes are at greater risk for cardiovascular disease, the leading cause of death among women and an independent risk factor for cognitive decline. Longitudinal epidemiologic studies report an association between diabetes mellitus and vascular dementia, but conflicting data on the association between diabetes and Alzheimer's dementia. Whether type 2 diabetes has an effect on cognitive function, independent of dementia, has received much attention since the 1980s, but the question remains unresolved.

METHOD

The literature was rigorously reviewed for studies in which cognitive functioning was measured with neuropsychological (NP) tests in participants with type 2 diabetes and a control/comparison group without diabetes.

RESULTS

Of 32 studies that reported the effects of type 2 diabetes on cognition in nondemented middle-aged and older adults, 30 included women in their samples, and two focused exclusively on women. Of studies that included women, 20 (67%) reported that participants with type 2 diabetes performed more poorly than those without diabetics on one or more NP tests, leading the authors to conclude that diabetes is positively associated with cognitive dysfunction.

CONCLUSIONS

Owing to the small number of studies with adequate numbers of women to report findings by gender, little is known about the effect of type 2 diabetes on cognition in women. It is critical that studies on type 2 diabetes and cognitive functioning be designed to include women in numbers adequate for examination of gender effects. The discussion addresses issues specific to women that warrant further research.

Diminished performance on response-selection tasks in Type 2 diabetes

Comparisons of visual perception, response-selection, and response-execution performance were made between Type 2 diabetes mellitus patients and a matched nondiabetic control group. 10 well-controlled male patients with Type 2 diabetes without diabetic complications (M age 58 yr.) and an age and IQ-matched non-diabetic control group consisting of 13 male healthy volunteers (M age 57 yr.) were included. Significant differences were found only between the two groups on response-selection performance, which concerns the selection and preparation of an appropriate motor action.

Nonopioid and neuropathy-specific analgesic action of the nootropic drug nefiracetam in mice

Nootropic drug nefiracetam and related compounds are used in diseases with learning and memory deficits. Recent studies have implicated relationships between learning, memory, and chronic pain. Thus, in the present report, we have studied the effects of nootropic drug nefiracetam on the thermal and mechanical hyperalgesia induced by partial sciatic nerve ligation or streptozotocin treatment in mice. In the thermal paw withdrawal test, p.o., s.c., i.t., and i.c.v. administration of nefiracetam dose dependently reversed the thermal hyperalgesia observed in nerve-injured mice. Nefiracetam (p.o. and i.t.) also significantly reversed the thermal hyperalgesia observed in streptozotocin-induced diabetic mice. In the paw pressure test, p.o. and i.t. administration of nefiracetam dose dependently reversed the mechanical hyperalgesia observed in both nerve-injured and diabetic mice. In contrast, nefiracetam had no effect in sham-operated or control nondiabetic mice in all paradigms. Among other pyrrolidine nootropics (p.o.), aniracetam produced significant analgesic effects. Other analogs also had some, but not significant, analgesic effects. Finally, nefiracetam (p.o.)-induced analgesia in injured mice was not affected by opioid antagonist naloxone (s.c., i.t., and i.c.v.) but was dose dependently inhibited by nicotinic antagonist mecamylamine (i.t. and i.c.v.). The analgesic effect of i.t. nefiracetam was also blocked by i.t. mecamylamine pretreatment. Together, these findings suggest that nefiracetam, a new member of the piracetam group of cognition enhancers, could be a good therapeutic tool against neuropathic pain. We also demonstrate that nefiracetam-induced analgesic action was nonopioid in nature and was due to stimulation of nicotinic cholinergic system at spinal and supraspinal levels.

Neuropsychological functioning in older people with type 2 diabetes: the effect of controlling for confounding factors

AIMS AND METHODS

Neuropsychological functioning was examined in a group of 33 older (mean age 62.40 +/- 9.62 years) people with Type 2 diabetes (Group 1) and 33 non-diabetic participants matched with Group 1 on age, sex, premorbid intelligence and presence of hypertension and cardio/cerebrovascular conditions (Group 2).

RESULTS

Data statistically corrected for confounding factors obtained from the diabetic group were compared with the matched control group. The results suggested small cognitive deficits in diabetic people's verbal memory and mental flexibility (Logical Memory A and SS7). No differences were seen between the two samples in simple and complex visuomotor attention, sustained complex visual attention, attention efficiency, mental double tracking, implicit memory, and self-reported memory problems.

CONCLUSIONS

These findings indicate minimal cognitive impairment in relatively uncomplicated Type 2 diabetes and demonstrate the importance of control and matching for confounding factors.

Effect of the treatment of Type II diabetes mellitus on the development of cognitive impairment and dementia

BACKGROUND

There is increasing interest in preventing cognitive impairment and dementia in later life. Epidemiological evidence shows a relationship between cognitive impairment and Type II diabetes. This association is stronger in patients who have been diagnosed for longer periods of time and in those who are on insulin therapy. There is little information on the short- and long-term influence of type of treatment and level of metabolic control on cognitive function of people with diabetes.

OBJECTIVES

To assess the effects of different types and intensities of treatments for Type II diabetes on cognitive function.

SEARCH STRATEGY

The Cochrane Control Trials Register, MEDLINE, EMBASE, PsycINFO, SIGLE LILACS and CINAHL as well as a number of ongoing trials databases were searched on 11 June 2002 using appropriate strategies.

SELECTION CRITERIA

Randomized controlled trials in which different treatments for Type II diabetes have been compared and in which measures of cognitive function were made at entry and after the treatment.

DATA COLLECTION AND ANALYSIS

Two reviewers independently assessed trial quality. Five trials were identified for possible inclusion but none of them could be included. In one, cognitive function was assessed before and after intensive or conventional diabetic treatment, but the comparison was not double-blind. The three other studies explored the effect of different treatments on QOL but did not include appropriate evaluation of cognitive function. The fifth did not report baseline data on cognitive function in the trial groups.

MAIN RESULTS

No studies were found to be appropriate for inclusion in meta-analysis.

REVIEWER'S CONCLUSIONS

There is no convincing evidence relating type or intensity of diabetic treatment to the prevention or management of cognitive impairment in Type II diabetes. Future research on treatments for diabetes should include standardized assessments of cognitive function as outcome measures.

Three-dimensional return map: a new tool for quantification of heart rate variability

BACKGROUND

Several methods are used to study heart rate variability, but they have limitations, which might be overcome by the use of a three-dimensional return map.

OBJECTIVES

To evaluate the performance of three-dimensional return map-derived indices to detect (1) sympathetic and parasympathetic modulation to the sinus node and (2) autonomic dysfunction in diabetic patients.

METHODS

Six healthy subjects underwent partial and total pharmacological autonomic blockade in a protocol that incorporated vagal and sympathetic predominance. Twenty-two patients with type 2 diabetes mellitus and 12 normal controls participated in the subsequent validation experiment. Three-dimensional return maps were constructed by plotting RRn intervals versus the difference between adjacent RR intervals [(RRn+1)-(RRn)] versus the number of counts, and four derived indices (P1, P2, P3, MN) were created for quantification.

RESULTS

Both indices P1 and MN were significantly increased after sympathetic blockade with propranolol, while all indices except P1 were modified after parasympathetic blockade (P < 0.05). During the validation experiments, P1 and MN detected differences between normal controls, and diabetic patients with and without autonomic neuropathy. The overall accuracy of most three-dimensional indices to detect autonomic dysfunction, estimated by the area under the ROC curve, was significantly better than traditional time domain indices. Three-dimensional return map-derived indices also showed adequate reproducibility on two different recording days (intra-class correlation coefficients of 0.69 to 0.82; P < 0.001).

CONCLUSIONS

Three-dimensional return map-derived indices are reproducible, quantify parasympathetic as well as sympathetic modulation to the sinus node, and are capable of detecting autonomic dysfunction in diabetic patients.

Type 2 diabetes mellitus, cognitive impairment and dementia

AIMS

We set out to examine the evidence for an association between cognitive impairment or dementia and the presence of Type 2 diabetes mellitus (DM). We also sought evidence of potential mechanisms for such an association.

METHODS

A literature search of three databases was performed and the reference lists of the papers so identified were examined, using English language papers only.

RESULTS

We found evidence of cross-sectional and prospective associations between Type 2 DM and cognitive impairment, probably both for memory and executive function. There is also evidence for an elevated risk of both vascular dementia and Alzheimer's disease in Type 2 DM albeit with strong interaction of other factors such as hypertension, dyslipidaemia and apolipoprotein E phenotype. Both vascular and non-vascular factors are likely to play a role in dementia in diabetes.

CONCLUSIONS

Current classification structures for dementia may not be adequate in diabetes, where mixed pathogenesis is likely. Further research into the mechanisms of cognitive impairment in Type 2 DM may allow us to challenge the concept of dementia, at least in these patients, as an irremediable disease.

Glucose intolerance, cognitive impairment and Alzheimer's disease

The literature on cognitive function and Alzheimer's disease in non-insulin-dependent diabetes, impaired glucose tolerance and hyperinsulinaemia are briefly summarized. Neuropsychological, epidemilogical and endocrine contributions are reviewed, with an emphasis on the insulin hypothesis as a potential pathophysiological mechanism for Alzheimer's disease.